RESUMO
Squid giant axons were injected simultaneously with Ca indicators Fura-2 and aequorin. Fura-2 was calibrated in situ by measuring fluorescence at 510 nm upon UV excitation at 340 nm, 360 nm, and 380 nm with a time-sharing multiple wavelength spectrofluorimeter. Limiting values for dye fluorescence were obtained by allowing a massive load of Ca to enter the axon with the aid of procedures such as prolonged depolarization in the presence of CN (for saturation) and by sequestration of all Ca present in the axoplasm accomplished with injection of EGTA into the axon (for a zero-Ca signal). The average intracellular Ca concentration obtained with Fura-2 was 184 nM. The sensitivity of Fura-2 to intracellular Ca is at least as great as that of aequorin, thus permitting its use in the characterization of Ca homeostasis mechanisms such as Na-Ca exchange. It was found, however, that for voltage-clamp experiments requiring an internal current electrode, Fura-2 is not a convenient Ca probe because electrode reactions in the axoplasm denature the dye, thereby restricting its use in characterization of Ca movements associated with electrically induced changes in membrane potential. A comparison of aequorin luminescence with Fura-2 fluorescence demonstrated that light output by aequorin is linear with intracellular Ca concentrations up to values of 750 nM, changing to a square law relationship from 750 nM up to 10 microM Ca.
Assuntos
Axônios/metabolismo , Cálcio/metabolismo , Equorina , Animais , Axônios/fisiologia , Decapodiformes , Estimulação Elétrica , Fura-2 , Técnicas In Vitro , Cinética , Lítio/metabolismo , Potenciais da Membrana , Microinjeções , Potássio/metabolismo , Sódio/metabolismoRESUMO
Squid giant axons were injected with aequorin and tetraethylammonium and were impaled with sodium ion sensitive, current and voltage electrodes. The axons were usually bathed in a solution of varying Ca2+ concentration ([Ca2+]o) containing 150mM each of Na+, K+ and an inert cation such as Li+, Tris or N-methylglucamine and had ionic currents pharmacologically blocked. Voltage clamp pulses were repeatedly delivered to the extent necessary to induce a change in the aequorin light emission, a measure of axoplasmic Ca2+ level, [Ca2+]i. The effect of membrane voltage on [Ca2+]i was found to depend on the concentration of internal Na+ ([Na+]i). Voltage clamp hyperpolarizing pulses were found to cause a reduction of [Ca2+]i. For depolarizing pulses a relationship between [Ca2+]i gain and [Na+]i indicates that Ca2+ entry is sigmoid with a half maximal response at 22 mM Na+. This Ca2+ entry is a steep function of [Na+]i suggesting that 4 Na+ ions are required to promote the influx of 1 Ca2+. There was little change in Ca2+ entry with depolarizing pulses when [Ca2+]o is varied from 1 to 10mM, while at 50mM [Ca2+]o calcium entry clearly increases suggesting an alternate pathway from that of Na+/Ca2+ exchange. This entry of Ca2+ at high [Ca2+]o, however, was not blocked by Cs+o. The results obtained lend further support to the notion that Na+/Ca2+ exchange in squid giant axon is sensitive to membrane voltage no matter whether this is applied as a constant change in membrane potential or as an intermittent one.
Assuntos
Axônios/metabolismo , Cálcio/metabolismo , Canais Iônicos/metabolismo , Equorina/farmacologia , Animais , Axônios/efeitos dos fármacos , Proteínas de Transporte/metabolismo , Decapodiformes , Cinética , Potenciais da Membrana , Potássio/metabolismo , Sódio/metabolismo , Trocador de Sódio e Cálcio , Tetraetilamônio , Compostos de Tetraetilamônio/farmacologiaRESUMO
The physiological and medical literature on the description of acute mountain sickness by Father Acosta in the Peruvian Andes shows many historical misconceptions and clinical misinterpretations. A recent paper by Gilbert (1983) not only contains these traditional misinterpretations but also adds geographical errors in the description of the area where Acosta described his sufferings. In view of these facts the authors have made a review of the old and modern writings on the so called Pariacaca story and during an on-site visit to the area of Pariacaca have taken actual measurements of distances, altitudes and geographical locations which they hope will put this story in the context of historical and scientific objectivity.
Assuntos
Doença da Altitude/história , Hipóxia/história , Doença Aguda , Adaptação Biológica , Adulto , Feminino , Geografia , História do Século XVI , Humanos , Masculino , Mapas como Assunto , Pessoa de Meia-Idade , PeruRESUMO
Measurements of whole blood O2 affinity were made with an automatic technique that allowed recording of O2 saturation continuously over a range of PO2 of 1 to 150 torr at constant pH and PCO2 with fresh samples of blood obtained from 5 natives of high altitude at Morococha, Peru (altitude, 4540 m). The results were not significantly different from those obtained with controls living at sea level with regard to the dlog P50/dpH slope at constant PCO2 or at constant base excess. Both results also agree with previous studies with normal sea-level blood. Thus earlier claims of an increased Bohr in Peruvian high-altitude natives is not supported.
Assuntos
Altitude , Oxigênio/sangue , Oxiemoglobinas/metabolismo , Adulto , Análise Química do Sangue , Humanos , Concentração de Íons de Hidrogênio , Medidas de Volume Pulmonar , Masculino , PeruAssuntos
Dimetadiona , Eritrócitos , Nicotina , Oxazóis , Feminino , Humanos , Concentração de Íons de Hidrogênio , MasculinoRESUMO
Chronic mountain sickness was first described in the Peruvian Andes. It consists of an excesive polycythemia for the altitude of residence. Its main symptoms are of cerebral congestion and occasionally of right heart insufficiency. The authors postulate that it is caused by a decay of the ventilatory rate with age with the corresponding increase in hematocrit.