RESUMEN
Using whole-cell voltage-clamp techniques, we investigated the protein kinase modulation of gamma-aminobutyric acid(C) (GABA(C))-activated currents relating to run-up regulation in dissociated cone-horizontal cell (HC) axon-terminals from catfish retina. GABA induced an inward chloride current in cells voltage-clamped at -70 mV. With repetitive applications of 10 microM GABA, the peaks of the GABA responses increased up to approximately 135% of the control responses during a period of 10 min. Intracellular application of forskolin, an adenylate cyclase activator, decreased the run-up of GABA(C) responses. H8 dihydrochloride, a cAMP inhibitor, enhanced this run-up to 190% of the control responses. 1-oleoyl-2-acetyl-sn-glycerol, a protein kinase C activator, accelerated the run-up of GABA(C) responses. GF 109203X, a PKC inhibitor, decreased the run-up. These results suggest that retinal GABA(C) responses in cone-HC axon-terminals are modulated by both protein kinase A and C.
Asunto(s)
Proteínas Quinasas Dependientes de AMP Cíclico/fisiología , Terminales Presinápticos/fisiología , Proteína Quinasa C/fisiología , Receptores de GABA/fisiología , Células Fotorreceptoras Retinianas Conos/fisiología , Adenilil Ciclasas/metabolismo , Animales , Bagres , AMP Cíclico/antagonistas & inhibidores , Activación Enzimática , Técnicas In Vitro , Técnicas de Placa-Clamp , Proteína Quinasa C/antagonistas & inhibidores , Células Fotorreceptoras Retinianas Conos/ultraestructura , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
Whole cell voltage-clamp recordings were performed on isolated terminals and somata from catfish retina to compare the distribution of excitatory and inhibitory receptors in both structures. Saturating concentrations of glutamate or kainate produced small currents in axon terminals, averaging less than 8% of the current evoked in the soma. In contrast, application of high concentrations of gamma-aminobutyric acid (GABA) produced approximately similar current amplitudes in both structures. Based on estimates of membrane surface area, GABA-induced current densities were around 0.05 pA/microm2 for both structures. The GABA-activated current in the axon terminal was not blocked by bicuculline or SR95531, but was completely inhibited by picrotoxin. Baclofen did not mimic the GABA effect, but trans-4-aminocrotonic acid (TACA, 300 microM) and muscimol (1 mM) elicited currents of 100 and 40 pA, respectively. These results suggest that the axon terminals of cone-horizontal cells possess GABA(C) receptors at a high density, do not possess GABA(A) or GABA(B) receptors, and have few glutamate receptors. The GABA(C) receptors could function as postsynaptic receptors in the inner plexiform layer or as autoreceptors.
Asunto(s)
Bagres/metabolismo , Terminales Presinápticos/metabolismo , Receptores de GABA/metabolismo , Retina/citología , Retina/metabolismo , Células Fotorreceptoras Retinianas Conos/metabolismo , Animales , Separación Celular , Estimulación Eléctrica , Electrofisiología , Agonistas de Aminoácidos Excitadores/farmacología , Agonistas del GABA/farmacología , Antagonistas del GABA/farmacología , Técnicas In Vitro , Potenciales de la Membrana/fisiología , Técnicas de Placa-Clamp , Ácido gamma-Aminobutírico/metabolismoRESUMEN
This paper reports the results of experiments on the antihepatoma effects of live targeted drug delivery system--lyophilized aclacinomycin A polyisobutylcyanoacrylate nanoparticle (ACM-IBC-NP) in vitro and in vivo. The median inhibition concentration were found to be 0.28 micrograms.ml-1 and 0.34 micrograms.ml-1 of lyophilized ACM-IBC-NP and ACM respectively in vitro. The inhibition ratio of colony formation were found to be 99% and 88% of lyophilized ACM-IBC-NP and ACM respectively in vitro. The antihepatoma activity was shown to be significantly concentration dependent. The results showed that lyophilized ACM-IBC-NP and ACM possess strong cytotoxicity on human hepatoma cell 7703, and the cytotoxicity was not significantly different between lyophilized ACM-IBC-NP and ACM in vitro. The model of orthotopic transplantation of human hepatoma in nude mice were used for evaluation of the activity of lyophilized ACM-IBC-NP against hepatoma. The tumor inhibition rate were found to be 86.84% for lyophilized ACM-IBC-NP and 46.69% for ACM. The cell proliferative activity of hepatoma were found to be 20.83% by lyophilized ACM-IBC-NP and 72.50% by ACM. All the results indicate that lyophilized ACM-IBC-NP and ACM have clinical application potential and the antihepatoma activity of lyophilized ACM-IBC-NP was obviously higher than that of ACM.
Asunto(s)
Aclarubicina/farmacología , Sistemas de Liberación de Medicamentos , Neoplasias Hepáticas/tratamiento farmacológico , Aclarubicina/administración & dosificación , Animales , Cianoacrilatos , Enbucrilato , Humanos , Neoplasias Hepáticas/patología , Ratones , Ratones Endogámicos BALB C , Ratones Desnudos , Microesferas , Trasplante de Neoplasias , Polímeros , Antígeno Nuclear de Célula en Proliferación/análisis , Células Tumorales Cultivadas/efectos de los fármacosRESUMEN
1. Baclofen, a gamma-aminobutyric acid (GABA)/B receptor agonist, was bath applied while recording the responses of second- and third-order neurons in the mudpuppy retina. Baclofen receptors were largely restricted to amacrine and ganglion cells. 2. Baclofen hyperpolarized the membrane potential of many, but not all, third-order neurons. This involved an increase in input conductance, probably associated with an opening of potassium channels. 3. The maximal increase in input conductance associated with the activation of GABA/B receptors was approximately one-third of that produced by activation of GABA/A receptors. 4. Baclofen suppressed sustained responses but enhanced transient responses. The net effect was that responses throughout the inner retina became more transient in the presence of baclofen. 5. In sustained cells baclofen not only suppressed the sustained responses but also revealed large transient responses. Thus baclofen converted the light responses of these cells from sustained to transient. This suggests that sustained cells receive significant transient excitation which is normally masked by the sustained inputs. 6. The role of the GABA/B receptor in controlling response characteristics and information content of amacrine and ganglion cells is discussed.
Asunto(s)
Baclofeno/farmacología , Retina/efectos de los fármacos , Animales , Conductividad Eléctrica , Técnicas In Vitro , Luz , Potenciales de la Membrana/efectos de los fármacos , Necturus , Neuronas/efectos de los fármacos , Neuronas/fisiología , Neuronas/efectos de la radiación , Receptores de GABA-A/efectos de los fármacos , Retina/citología , Retina/fisiología , Retina/efectos de la radiación , Factores de TiempoRESUMEN
1. Baclofen increases transient light responses of amacrine and ganglion cells despite acting as a classical inhibitory transmitter to both hyperpolarize and shunt these cells. 2. This effect seems to occur at the level of the inner retina and appears not to be due to an additional input from bipolar cells. 3. In some transient cells baclofen increases the total amplitude of the light response but does not change the peak potential of the light evoked EPSP. In these cells, the baclofen-induced enhancement can be accounted for by an increase in driving force of the excitatory postsynaptic potential (EPSP) resulting from the hyperpolarization. 4. However, in other cells the peak of the light response after baclofen application is greater, which cannot be accounted for by a change in driving force. This effect of baclofen can be mimicked by a blockers of gamma-aminobutyric acid (GABA) and glycine, suggesting that in these cells baclofen's enhancement is due in part to network effects resulting in a removal of sustained inhibition. 5. Therefore, the paradoxical effect of an inhibitory transmitter producing an enhancement of synaptic responses seems due to at least two mechanisms. 6. The results indicate that some transient cells receive significant tonic inhibition which limits their response amplitude in a push-pull type mechanism, but other cells are not under this inhibitory control process.