RESUMEN

1. The mechanisms responsible for sensing hypoxia and initiating hypoxic pulmonary vasoconstriction (HPV) are unclear. We therefore examined the roles of the mitochondrial electron transport chain (ETC) and glycolysis in HPV of rat small intrapulmonary arteries (IPAs). 2. HPV demonstrated a transient constriction (phase 1) superimposed on a sustained constriction (phase 2). Inhibition of complex I of the ETC with rotenone (100 nM) or complex III with myxothiazol (100 nM) did not cause vasoconstriction in normoxia, but abolished both phases of HPV. Rotenone inhibited the hypoxia-induced rise in intracellular Ca(2+) ([Ca(2+)](i)). Succinate (5 mM), a substrate for complex II, reversed the effects of rotenone but not myxothiazol on HPV, but did not affect the rise in NAD(P)H fluorescence induced by hypoxia or rotenone. Inhibition of cytochrome oxidase with cyanide (100 microM) potentiated phase 2 constriction. 3. Phase 2 of HPV, but not phase 1, was highly correlated with glucose concentration, being potentiated by 15 mM but abolished in its absence, or following inhibition of glycolysis by iodoacetate or 2-deoxyglucose. Glucose concentration did not affect the rise in [Ca(2+)](i) during HPV. 4. Depolarisation-induced constriction was unaffected by hypoxia except in the absence of glucose, when it was depressed by approximately 50 %. Depolarisation-induced constriction was depressed by rotenone during hypoxia by 23 +/- 4 %; cyanide was without effect. 5. Hypoxia increased 2-deoxy-[(3)H]glucose uptake in endothelium-denuded IPAs by 235 +/- 32 %, and in mesenteric arteries by 218 +/- 38 %. 6. We conclude that complex III of the mitochondrial ETC acts as the hypoxic sensor in HPV, and initiates the rise in smooth muscle [Ca(2+)](i) by a mechanism unrelated to changes in cytosolic redox state per se, but more probably by increased production of superoxide. Additionally, glucose and glycolysis are essential for development of the sustained phase 2 of HPV, and support an endothelium-dependent Ca(2+)-sensitisation pathway rather than the rise in [Ca(2+)](i).

Asunto(s)

Glucólisis/fisiología , Hipoxia/metabolismo , Mitocondrias/metabolismo , Circulación Pulmonar/fisiología , Vasoconstricción/fisiología , Animales , Antimetabolitos/farmacología , Cianuros/farmacología , Desoxiglucosa/farmacología , Transporte de Electrón/efectos de los fármacos , Transporte de Electrón/fisiología , Complejo III de Transporte de Electrones/metabolismo , Inhibidores Enzimáticos/farmacología , Glucosa/farmacología , Glucólisis/efectos de los fármacos , Hipoglucemiantes/farmacología , Insulina/farmacología , Yodoacetatos/farmacología , Masculino , Arterias Mesentéricas/fisiología , Metacrilatos , Mitocondrias/efectos de los fármacos , NADP/metabolismo , Arteria Pulmonar/fisiología , Ratas , Ratas Wistar , Rotenona/farmacología , Ácido Succínico/farmacología , Tiazoles/farmacología , Desacopladores/farmacología

RESUMEN

We examined the mechanisms underlying leukotriene D4- (LTD4) induced constriction of human small (300 - 500 micron i.d.) bronchioles, and the effect of LTD4 on ion currents and Ca2+ transients in smooth muscle cells (SMC) isolated from these bronchioles. LTD4 caused a concentration-dependent bronchoconstriction with an EC50=0.58+/-0.05 nM (n=7) which was not easily reversible upon washout. This bronchoconstriction was entirely dependent on extracellular Ca2+. Blockade of L-type Ca2+ channels with nifedipine (10 microM) reduced LTD4 response by 39+/-2% (n=8), whilst La3+, Gd3+ and SK&F 96,365 abolished LTD4-induced bronchoconstriction completely and reversibly, suggesting the majority of Ca2+ entry was via non-selective cation channels. Antagonists of PI-PLC (U73,122 and ET-18-OCH3), PLD (propranolol) and PKC (cheleretrine and Ro31-8220) were without any effect on LTD4-induced bronchoconstriction, whilst the PC-PLC inhibitor D609 caused complete relaxation. Inhibition of protein tyrosine kinase with tyrphostin A23 (100 microM) caused about 50% relaxation, although the inactive analogue tyrphostin A1 was without effect. In freshly isolated SMC from human small bronchioles LTD4 caused a slow increase of intracellular Ca2+ concentration, with a consequent rise of the activity of large conductance Ca2+-dependent K+ channels and the amplitude of depolarization-induced outward whole-cell current. Again, no effect of LTD4 could be observed in the absence of extracellular Ca2+. We conclude that LTD4 causes constriction of these small bronchioles primarily by activating Ca2+ entry via non-voltage gated channels, possibly by a PC-PLC mediated pathway.

Asunto(s)

Bronquios/efectos de los fármacos , Broncoconstricción/efectos de los fármacos , Señalización del Calcio/fisiología , Leucotrieno D4/farmacología , Anciano , Anciano de 80 o más Años , Bronquios/citología , Calcio/metabolismo , Señalización del Calcio/efectos de los fármacos , Separación Celular , Electrofisiología , Humanos , Técnicas In Vitro , Persona de Mediana Edad , Contracción Muscular/efectos de los fármacos , Tono Muscular/efectos de los fármacos , Tono Muscular/fisiología , Músculo Liso/citología , Músculo Liso/efectos de los fármacos , Técnicas de Placa-Clamp

RESUMEN

Bronchoconstriction of small bronchioles plays a major role in the increase in airway resistance following agonist challenge. There is evidence that the airway smooth muscle (ASM) of small bronchioles differs functionally from that in larger airways. Little is known however about the electrophysiology of small bronchioles. Ion currents were therefore studied in airway smooth muscle cells freshly dissociated from human intralobular bronchioles, with a diameter between 0.3 and 1.0 mm. As previously reported for human large airways, the major outward current in these cells was due to activity of large conductance K+ (BK) channels, with a relatively minor component due to a voltage-gated delayed rectifier current (IDR), which was only observed in 30 % of cells. Three distinct types of iberiotoxin- and TEA-sensitive large conductance K+ channel contributed to large conductance K+ current (IBK). These included a highly voltage- and Ca2+-sensitive 200 pS channel previously reported in human large airways, and two smaller channels of 150 and 100 pS previously seen only in human fetal or cultured ASM. In contrast to large airways, ASM cells from bronchioles also demonstrated a voltage-gated inward rectifier current (IIR). IIR was activated by hyperpolarisation below the K+ equilibrium potential and could be blocked by submillimolar concentrations of Cs+ or Ba2+, and partially by physiological concentrations of Na+. Corresponding single channels with a conductance of 17 pS could also be recorded in the cell-attached configuration. A small voltage-independent current was also observed which was resistant to classic K+ and Cl- channel blockers but which could be abolished by replacement of Na+ with the impermeant cation N-methyl-D-glucamine (NMDG+). Corresponding non-selective single channels of 20 pS could be seen in inside-out mode. These results demonstrate that ASM from small bronchioles differs in terms of ion currents and channels from ASM derived from large airways, with possible implications for function.

Asunto(s)

Bronquios/metabolismo , Músculo Liso/metabolismo , Canales de Potasio/fisiología , Bronquios/citología , Calcio/farmacología , Conductividad Eléctrica , Humanos , Activación del Canal Iónico , Músculo Liso/citología , Péptidos/farmacología , Bloqueadores de los Canales de Potasio , Canales de Potasio/clasificación , Tetraetilamonio/farmacología

RESUMEN

Ion channels underlying the resting membrane potential were examined in human fetal airway smooth muscle (ASM). Tissue was obtained from the Medical Research Council Tissue Bank, London, UK. ASM cells were enzymatically dispersed, and ion currents were examined using a patch clamp. Although all cells were of similar size and stained intensely for vimentin, only approximately 50% stained intensely for smooth muscle alpha-actin or myosin heavy chain. Depolarization induced a tetraethylammonium (TEA)- and charybdotoxin (ChTX)-sensitive outward current that varied widely among cells (<50 to >2000 pA at +100 mV), and a smaller nonselective cation current that was similar in all cells (approximately 20 pA at +100 mV). The TEA-sensitive current was associated with three types of large conductance, ChTX-sensitive K+ channel: a 200-pS channel, which was active at negative potentials and low [Ca2+], as described for freshly isolated adult ASM, and two other K+ channels of 100 and 150 pS, previously observed only in adult ASM proliferating in culture. ChTX, but not 4-aminopyridine, caused a substantial depolarization in the current clamp mode, suggesting that, in contrast to ASM from other species or vascular smooth muscle, large conductance K+ channels rather than a delayed rectifier are the major determinant of membrane potential in this tissue. Our results show a distinct similarity between fetal ASM and adult ASM proliferating in culture. We suggest that the heterogeneity in current density and staining reflect different degrees of differentiation, rather than different cell types, and that the 100- and 150-pS K+ channels are specifically associated with a proliferative phenotype in human ASM.

Asunto(s)

Músculo Liso/embriología , Músculo Liso/fisiología , Canales de Potasio/fisiología , Tráquea/embriología , Tráquea/fisiología , Aborto Inducido , Adulto , Células Cultivadas , Electrofisiología , Femenino , Humanos , Inmunohistoquímica , Embarazo

RESUMEN

The nicotinic acetylcholine receptor (AChR) exhibits at least four different conformational states varying in affinity for agonists such as acetylcholine (ACh). Photoaffinity labeling has been previously used to elucidate the topography of the AChR. However, to date, the photosensitive probes used to explore the cholinergic binding site photolabeled only closed or desensitized states of the receptor. To identify the structural modifications occurring at the ACh binding site on allosteric transition associated with receptor activation, we have investigated novel photoactivatable 4-diazocyclohexa-2,5-dienone derivatives as putative cholinergic agonists. Such compounds are fairly stable in the dark and generate highly reactive carbenic species on irradiation. In binding experiments using AChRs from Torpedo marmorata, these ligands had affinities for the ACh binding site in the micromolar range and did not interact with the noncompetitive blocker site (greater than millimolar affinity). Irreversible photoinactivation of ACh binding sites was obtained with the ligand 1b (up to 42% at 500 microM) in a protectable manner. In patch-clamp studies, 1b was shown to be a functional agonist of peripheral AChR in TE 671 cells, with the interesting property of exhibiting no or very little desensitization even at high concentrations.

Asunto(s)

Marcadores de Afinidad/química , Compuestos de Diazonio/química , Agonistas Nicotínicos/química , Agonistas Nicotínicos/farmacología , Fotoquímica , Acetilcolina/farmacología , Animales , Sitios de Unión/fisiología , Electrofisiología , Ligandos , Agonistas Nicotínicos/metabolismo , Antagonistas Nicotínicos/química , Antagonistas Nicotínicos/metabolismo , Antagonistas Nicotínicos/farmacología , Torpedo

RESUMEN

Large conductance Ca(2+)-dependent K+ channels were studied in smooth muscle cells enzymatically dissociated from rabbit pulmonary artery. The current-voltage relationship of single channels recorded in cell-attached patches revealed strong inward rectification, which disappeared after patch excision. Cell permeabilization with saponin, beta-escin or equinatoxin II also removed rectification. These observations imply the existence of fast open channel block by an intracellular substance(s). Application to the cytosolic side of inside-out patches of Na+ ions, mono- di- and trinucleotides, taurine, reduced and oxidized forms of glutathione, or peptides extracted from pulmonary artery smooth muscle, did not reproduce the inward rectification. Patch treatment with either alkaline phosphatase or protein kinase A alpha-subunit, which strongly affected open state probability, was also incapable of reducing the outward single channel current. Mg2+ ions applied from the cytosolic side induced concentration- and voltage-dependent block of the outward single channel currents with a Kd of 7.9 +/- 2.3 mM, resulting in inward rectification qualitatively similar to that observed in cell-attached patches. An increase in the Mg2+ concentration of the intracellular solution induced a significant decrease in the outward whole-cell current at depolarized potentials. Another putative endogenous channel blocker, the polyamine putrescine, was not effective. However, its metabolites spermidine and spermine reduced the amplitude of the outward single channel current with Kd values of 4.9 +/- 0.6 and 1.4 +/- 0.4 mM, respectively. Pre-incubation of the cells with the irreversible inhibitor of polyamine synthesis difluoromethylornithine abolished the rectification in the cell-attached patches. These results suggest that intracellular polyamines may underlie at least part of the inward rectification of the Ca2+ activated K+ channel in this tissue, but that intracellular Mg2+ is unlikely to play a major role.

Asunto(s)

Músculo Liso Vascular/metabolismo , Canales de Potasio Calcio-Activados , Canales de Potasio/metabolismo , Arteria Pulmonar/metabolismo , Animales , Eflornitina/farmacología , Subunidades alfa de los Canales de Potasio de Gran Conductancia Activados por Calcio , Canales de Potasio de Gran Conductancia Activados por el Calcio , Magnesio/metabolismo , Masculino , Canales de Potasio/efectos de los fármacos , Putrescina/farmacología , Conejos

RESUMEN

Voltage-gated ion currents were studied in human bronchial airway smooth muscle (ASM) cells. Proliferating or growth-arrested cells in culture were compared with freshly isolated cells. Three types of charybdotoxin (ChTX)-sensitive K+ channel were observed in all cell types, with conductances in symmetrical 140 mM KCl solutions ([Ca2+]i < 0.1 nM) of 206 +/- 14 pS (n = 32), 144 +/- 11 pS (n = 27) and 109 +/- 5 pS (n = 25). The relative proportion of each channel type differed substantially between the three groups of cells. In freshly isolated ASM cells large conductance K+ channels were represented almost entirely by a conductance of 206 pS, which was found in all twenty-three patches studied. In contrast, in most patches from proliferating cells the majority of channels had conductances of either 144 pS (14 of 21 patches) or 109 pS (8 of 21 patches). Cultured cells that had been growth arrested by serum depletion revealed the same set of channels as the proliferating cells, but the occurrence of the 109 pS channel was much more frequent (16 of 19 patches). As has been shown previously, 206 pS channels were active at a physiological membrane potential (-60 to -20 mV) even at a very low free [Ca2+]. The 144 pS channels could be recorded only at depolarized potentials (+80 to +100 mV), whereas 109 pS channels were active over a wide range of potentials (-60 to +100 mV), but only in the presence of GTP. In a proportion of cultured cells a tetrodotoxin-sensitive Na+ current and a hyperpolarization-induced inwardly rectifying K+ current were also observed (15 and 21%, respectively, of all cells examined). Neither of these currents were observed in freshly isolated cells. Whole-cell outward current in all groups was sensitive to tetraethylammonium, ChTX, and iberiotoxin, but not to 4-aminopyridine. In summary, it is clear that during proliferation there are considerable changes in the expression of ionic channels in ASM that have profound functional significance. In particular, these changes would tend to make the tissue more excitable, and may be of relevance to the proliferative process itself.

Asunto(s)

Bronquios/fisiología , Músculo Liso/fisiología , Canales de Potasio Calcio-Activados , Canales de Potasio/fisiología , Adulto , Anciano , Anciano de 80 o más Años , Cadmio/metabolismo , Calcio/metabolismo , Células Cultivadas , Femenino , Guanosina 5'-O-(3-Tiotrifosfato)/farmacología , Humanos , Canales de Potasio de Gran Conductancia Activados por el Calcio , Masculino , Persona de Mediana Edad , Péptidos/farmacología , Venenos de Escorpión/farmacología , Canales de Sodio/efectos de los fármacos , Canales de Sodio/fisiología

RESUMEN

1. K+ currents were studied in smooth muscle cells enzymatically dissociated from human bronchi, by use of the patch-clamp technique. 2. In whole-cell recordings a depolarization-induced, 4-aminopyridine (4-AP)-sensitive current was observed in only 26 of 155 cells, and in 20 of these 26 cells its amplitude at a test potential of 0 mV was less than 100 pA. 3. In the majority of cells depolarization to -40 mV or more positive potentials induced a noisy outward current which activated within milliseconds and showed almost no inactivation even during a 5 s depolarizing voltage step. This current was insensitive to 4-AP (up to 5 mM) but was strongly inhibited in the presence of tetraethylammonium (TEA, 1 mM), charybdotoxin (ChTX, 100 nM) or iberiotoxin (IbTX, 50 nM) in the bath. The same current was also recorded by the nystatin-perforated patch technique. 4. Single channels with a conductance of about 210 pS were recorded in cell-attached patch, inside-out patch, outside-out patch and whole-cell recording configurations. Channel open state probability in inside-out patches was 0.5 at a membrane potential of 4 +/- 14 mV (mean +/- s.d., n = 13) mV even with a free Ca2+ concentration on the cytosolic side of the patch of less than 0.1 nM. Open state probability increased with depolarization and internal Ca2+ concentration. Single channels could be reversibly blocked by externally applied TEA, ChTX and IbTX. 5. In current-clamp recordings with 100 nM free Ca2+ in the intracellular solution both TEA and ChTX caused substantial concentration-dependent depolarization. 6. These results suggest that in human bronchial smooth muscle cells, in marked contrast to other species, the majority of the outward current induced by depolarization is not due to a delayed rectifier,but to the activity of a large conductance, ChTX-sensitive K+ channel. The Ca2+- and voltage-dependency of this channel may well allow a sufficiently high open state probability for it to play a partin the regulation of the resting membrane potential.

Asunto(s)

Bronquios/efectos de los fármacos , Músculo Liso/fisiología , Canales de Potasio/fisiología , Adulto , Anciano , Femenino , Humanos , Masculino , Potenciales de la Membrana/efectos de los fármacos , Persona de Mediana Edad , Técnicas de Placa-Clamp , Péptidos/farmacología , Neumonectomía

RESUMEN

The influence of alkaline earth metal ions calcium and magnesium on the conductance and on the kinetics of activation and atropine-induced blockade of nicotinic cholinoreceptor ion channels in cultured rat skeletal muscle were studied using patch-clamp technique. In physiological concentrations these cations influence both conductance and kinetics of blockade, but have no significant effect on the kinetics parameters of activation. The data suggest that physiological cations modulate the generation of postsynaptic potentials in the normal condition as well as in the presence of blocking drugs.

Asunto(s)

Activación del Canal Iónico/efectos de los fármacos , Canales Iónicos/efectos de los fármacos , Metales Alcalinotérreos/farmacología , Músculo Esquelético/efectos de los fármacos , Receptores Nicotínicos/efectos de los fármacos , Acetilcolina/farmacología , Animales , Atropina/farmacología , Calcio/farmacología , Cationes Bivalentes , Células Cultivadas , Activación del Canal Iónico/fisiología , Canales Iónicos/fisiología , Magnesio/farmacología , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Músculo Esquelético/fisiología , Ratas , Receptores Nicotínicos/fisiología

RESUMEN

Using patch-clamp and Indo-1AM techniques, we studied the effects of prostaglandins (PG) E1 and E2 on transmembrane ionic currents and cytosolic calcium concentration ([Ca2+]i) in cultured rat aortic smooth muscle cells (SMC) and on isotonic contraction-relaxation of strips of the rat thoracic aorta. In voltage-clamped at -70 mV single SMC PGE1 and PGE2 in concentration 100 nM evoked inward and outward currents. The inward current was unaffected by the Cl channel blocker DIDS (0.1 mM). The outward current was blocked by internal Cs+ and external Ba2+ and was likely due to increased Ca2+ activated K+ conductance. Application of PGE1 and PGE2 in the bath solution evoked relaxation of aortic strips in a concentration-dependent manner. In both cases indomethacin was ineffective. The rise in [Ca2]i evoked by PGEs was observed in single cells loaded with Indo-1AM. Whole-cell voltage-activated T- and L-type Ca2+ currents were reduced by both PGE1 and PGE2. The results obtained in this work indicate that in cultured rat aortic SMC PGE1 and PGE2 increase [Ca2+]i with subsequent activation of Ca(2+)-dependent K+ currents, block voltage-activated Ca2+ currents, and at the same time induce relaxation of aortic strips.

Asunto(s)

Alprostadil/farmacología , Aorta/efectos de los fármacos , Dinoprostona/farmacología , Músculo Liso Vascular/efectos de los fármacos , Animales , Aorta/fisiología , Calcio/metabolismo , Células Cultivadas , Técnicas In Vitro , Contracción Isotónica/efectos de los fármacos , Potenciales de la Membrana , Músculo Liso Vascular/citología , Músculo Liso Vascular/fisiología , Canales de Potasio/efectos de los fármacos , Canales de Potasio/fisiología , Ratas , Ratas Endogámicas WKY , Canales de Sodio/efectos de los fármacos , Canales de Sodio/fisiología

RESUMEN

1. Membrane ionic currents provoked by externally applied ATP were studied by patch-clamp techniques in cultured aortic smooth muscle cells of the rat. 2. Using standard bath and pipette solutions and whole-cell voltage-clamp, ATP evoked an inward current when the cell membrane potential was held at -50 mV and an outward current when the potential was held at 30 mV, with a reversal potential near -10 mV. 3. Application of ATP gamma S gave results similar to those obtained with ATP, while adenosine, AMP and alpha,beta-methylene ATP were ineffective. The ATP-activated current was inhibited by suramin, 100 microM. 4. ATP also induced a biphasic rise in internal free Ca levels as shown directly by Fura-2 measurements and by the increase in Ca-dependent K single-channel activity in cell-attached patches. 5. With outward current through K channels blocked by internal Cs and TEA, modification of the ionic composition of bath and pipette solutions revealed that the reversal potential for the ATP-induced whole-cell current closely followed ECl, the chloride equilibrium potential, and was insensitive to manipulations of the monovalent cation gradient. 6. These results indicate that in rat cultured aortic smooth muscle cells, ATP binding to P2-purinoceptors produces increases of internal free Ca levels and subsequent activation of both Ca-dependent K and Cl currents.

Asunto(s)

Adenosina Trifosfato/farmacología , Músculo Liso Vascular/efectos de los fármacos , Adenosina Trifosfato/análogos & derivados , Animales , Aorta Torácica/efectos de los fármacos , Calcio/metabolismo , Canales de Calcio/efectos de los fármacos , Células Cultivadas , Electrofisiología , Masculino , Potenciales de la Membrana/efectos de los fármacos , Contracción Muscular/efectos de los fármacos , Fenotipo , Ratas , Ratas Endogámicas WKY

Asunto(s)

Muñones de Amputación/diagnóstico por imagen , Huesos/diagnóstico por imagen , Pierna/diagnóstico por imagen , Humanos , Osteoporosis/diagnóstico por imagen , Radiografía

RESUMEN

The treatment of m. cutaneus pectoris-n. pectoralis preparations with 0.5 microM of alkylating derivate of hexadecamethonium, hexadecamethylene-bis-methylchloroethylamine, led to irreversible decrease of the amplitude of EPPs. The decrease was shown to be of a postsynaptic nature. After pretreatment of the neuromuscular preparations with alkylating derivate the effects of cholinesterase inhibitors were strongly diminished.

Asunto(s)

Alquilantes/farmacología , Compuestos de Decametonio/farmacología , Unión Neuromuscular/efectos de los fármacos , Compuestos de Mostaza Nitrogenada/farmacología , Transmisión Sináptica/efectos de los fármacos , Animales , Inhibidores de la Colinesterasa/farmacología , Interacciones Farmacológicas , Técnicas In Vitro , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Microelectrodos , Placa Motora/efectos de los fármacos , Placa Motora/fisiología , Unión Neuromuscular/fisiología , Rana temporaria , Sinapsis/efectos de los fármacos , Sinapsis/fisiología , Transmisión Sináptica/fisiología

RESUMEN

Bath application of 0.5 and 2 microM acetylcholine (ACh) slowed the decay phase of miniature endplate currents (MEPC) recorded in isolated, voltage-clamped and prostigmine-treated frog sartorius muscle. Washout of ACh led to a decrease of the decay time constant of the MEPC to 72 +/- 5% (n = 5) and 51 +/- 3% (n = 6) of initial values, respectively, followed by very slow and incomplete recovery. MEPC amplitude changed slightly and recovered relatively fast. This discrepancy in the recovery rates is suggested to be due to a 'trapping' ability of desensitized receptors which can compete with the free receptors for ACh molecules and prevent repetitive binding. Thus the high affinity of desensitized receptors to ACh may partially compensate the absence of acetylcholinesterase activity.

Asunto(s)

Acetilcolina/farmacología , Placa Motora/fisiología , Músculos/fisiología , Unión Neuromuscular/fisiología , Rana temporaria/fisiología , Receptores Colinérgicos/fisiología , Animales , Bungarotoxinas/farmacología , Técnicas In Vitro , Potenciales de la Membrana/efectos de los fármacos , Placa Motora/efectos de los fármacos , Músculos/efectos de los fármacos , Receptores Colinérgicos/efectos de los fármacos

RESUMEN

Intracellular pressure injection of potassium salt solution has been studied for its effect on the receptor potential of the slowly adapting stretch receptor of crayfish. It was found that the injection caused an increase in the static phase of the receptor potential. The results suggest that the intracellular hydrostatic pressure may be involved in generation of primary receptor responses of mechanoreceptors.

Asunto(s)

Astacoidea/efectos de los fármacos , Mecanorreceptores/efectos de los fármacos , Neuronas/efectos de los fármacos , Animales , Astacoidea/fisiología , Electrofisiología , Técnicas In Vitro , Mecanorreceptores/fisiología , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Microinyecciones/instrumentación , Microinyecciones/métodos , Neuronas/fisiología , Presión , Soluciones

RESUMEN

1. The amplitudes of end-plate currents (EPCs) in short trains of fifteen to seventeen EPCs at 10 Hz were depressed in the presence of 10 microM-proadifen when acetylcholinesterase (AChE) was inhibited. 2. The proadifen-induced EPC depression was voltage-dependent and the effect was more pronounced at negative membrane potentials. 3. In the presence of proadifen, the mean amplitude of miniature end-plate currents (MEPCs) was reduced by 36% 5 s after the EPC train as compared with MEPCs before the train. 4. Without proadifen, but with inhibited AChE, an increase of temperature from 20 to 26 degrees C and elevation of external Ca2+ from 1.8 to 2.5 mM led to EPC amplitude depression in the train, which was also potential-dependent. 5. After AChE inhibition, proadifen (10 microM) progressively shortened MEPC decay without significant reduction of amplitude up to 40 min of exposition. MEPCs were not affected by proadifen when AChE was active. 6. It is concluded that these postsynaptic effects of proadifen can be explained neither by its action on the resting acetylcholine receptors (AChR) nor on open ion channels but are due to its desensitization-promoting action.

Asunto(s)

Placa Motora/fisiología , Unión Neuromuscular/fisiología , Receptores Colinérgicos/fisiología , Animales , Inhibidores de la Colinesterasa/farmacología , Electrofisiología , Técnicas In Vitro , Placa Motora/efectos de los fármacos , Proadifeno/farmacología , Rana ridibunda , Rana temporaria , Receptores Colinérgicos/efectos de los fármacos

RESUMEN

Numerical model showing action of open channel blockers on the neuromuscular junction is described. Quantitative aspects of the simple blocking action are analyzed and criteria which allow discriminating between channel blocking action and channel kinetics modification are suggested. The results of simulation are compared with experimental data. Some peculiarities of channel blocking drug action after acetylcholinesterase inhibition are discussed.

Asunto(s)

Inhibidores de la Colinesterasa/farmacología , Canales Iónicos/efectos de los fármacos , Sinapsis/efectos de los fármacos , Animales , Matemática

RESUMEN

The patch clamp technique was used to examine the properties of an inward-rectifying potassium channel in the cell membrane of freshwater mollusc Planorbarius corneus neurons. Inward currents of single channels were observed at potentials more negative than potassium equilibrium potential (EK), when microelectrode contained potassium ions (50 mmol/l) and potassium channel blockers: tetraethylammonium, barium or cesium ions (10-20 mmol/l). The conductance of the single channel was equal to 81 +/- 12 pS at 50 mmol/l potassium ion concentration in the patch electrode. At potentials more positive than EK the conductance sharply decreased to 0 pS. The times of the open state of the closed one of the channel and probability of the open state existing for the ionic channel were estimated with various constant potentials. It was revealed that the channel openings were grouped in bursts. The lifetime of the open state and burst duration decreased with hypopolarization of the patch.

Asunto(s)

Moluscos/fisiología , Neuronas/fisiología , Canales de Potasio/fisiología , Potenciales de Acción/efectos de los fármacos , Animales , Bario/farmacología , Membrana Celular/efectos de los fármacos , Membrana Celular/fisiología , Cesio/farmacología , Microelectrodos , Neuronas/efectos de los fármacos , Canales de Potasio/efectos de los fármacos , Compuestos de Tetraetilamonio/farmacología

RESUMEN

The numerical model of the miniature end-plate current MEPC described earlier was systematically analyzed to obtain an optimal set of parameters. This set permits simulating a number of experimental effects: time course of normal MEPC, cholinesterase inhibition, alpha-bungarotoxin action, potential dependence of MEPC, etc. The time course of the simulated "giant" MEPC fitted the experimental data only partially. A good correspondence between the model and experimental data underlies the conclusion that this model reflects well the relative contribution of several processes to MEPC generation.

Asunto(s)

Modelos Biológicos , Placa Motora/fisiología , Unión Neuromuscular/fisiología , Animales , Bungarotoxinas/farmacología , Inhibidores de la Colinesterasa/farmacología , Matemática , Potenciales de la Membrana/efectos de los fármacos , Placa Motora/efectos de los fármacos

Asunto(s)

Atropina/farmacología , Canales Iónicos/efectos de los fármacos , Músculos/fisiología , Receptores Nicotínicos/efectos de los fármacos , Animales , Técnicas In Vitro , Canales Iónicos/fisiología , Potenciales de la Membrana/efectos de los fármacos , Músculos/efectos de los fármacos , Ratas , Receptores Nicotínicos/fisiología