Calvo S, Granja R, González-García C, Ceña V
Departamento de Farmacología y Terapéutica, Universidad de Alicante, Spain.
Neuroscience. 1995 Sep;68(1):265-72. doi: 10.1016/0306-4522(95)00132-3.
In this paper, we show that exposure of chromaffin cells to high K+ (75 mM) for 5 min releases about 15% of total norepinephrine and 8% of total epinephrine contained in chromaffin cells. The measured resting membrane potential of these cells was -55 mV. Long (10 s) depolarizing electrical pulses applied from a holding potential of -55 mV to 5 mV, that would produce a depolarization similar to exposure to high K+ (75 mM), induced an inward Ca2+ current that inactivated with a time constant of about 0.8 s and promoted the influx of about 1 fmol of Ca2+ into the cell. Both high K+ and electrically-induced depolarization increased intracellular Ca2+ levels to a similar value (about 350 nM). Extrapolation would indicate that total Ca2+ influx in high K+ (75 mM)-stimulated 10(6) chromaffin cells would amount to 1 nmol which would promote the secretion of about 4.9 nmol of norepinephrine and 3.5 nmol of epinephrine from 10(6) chromaffin cells. The results indicate that Ca2+ influx in response to depolarization is short-lived, likely due to Ca(2+)-dependent inactivation of voltage-dependent Ca2+ channels. However, intracellular Ca2+ levels remain high as long as depolarization is present and long after Ca2+ influx has ceased. This would suggest that some processes related to either Ca2+ buffering or extrusion from the cell may be voltage dependent.
在本文中，我们发现嗜铬细胞暴露于高钾（75 mM）5分钟会释放出嗜铬细胞中约15%的去甲肾上腺素总量和8%的肾上腺素总量。这些细胞测得的静息膜电位为-55 mV。从-55 mV的钳制电位施加到5 mV的长（10秒）去极化电脉冲，这会产生与暴露于高钾（75 mM）相似的去极化，诱导出内向钙电流，该电流以约0.8秒的时间常数失活，并促进约1飞摩尔的钙离子流入细胞。高钾和电诱导的去极化都将细胞内钙离子水平提高到相似的值（约350 nM）。外推表明，在高钾（75 mM）刺激下，10⁶个嗜铬细胞中的总钙离子流入量将达到1纳摩尔，这将促进10⁶个嗜铬细胞分泌约4.9纳摩尔的去甲肾上腺素和3.5纳摩尔的肾上腺素。结果表明，去极化引起的钙离子流入是短暂的，可能是由于电压依赖性钙通道的钙依赖性失活。然而，只要存在去极化，并且在钙离子流入停止很久之后，细胞内钙离子水平仍保持较高。这表明一些与钙离子缓冲或从细胞中排出相关的过程可能是电压依赖性的。
