Eusebi F, Miledi R, Takahashi T
J Physiol. 1983 Jul;340:91-106. doi: 10.1113/jphysiol.1983.sp014751.
Intracellular Ca2+ transients, evoked either by action potentials or depolarizing clamp pulses, were studied in frog sartorius muscle fibres injected with aequorin. The time course of the Ca2+ transients became shorter as the temperature was increased. The half rise time and decay time constants showed straight lines between 3 and 30 degrees C in Arrhenius plots, with a Q10 of 2.5 and 2.3 respectively. The potential dependence of the Ca2+ transient was examined under voltage clamp. The peak light amplitude reached a plateau at around +50 mV, suggesting that Ca2+ release continues beyond the potential level at which contraction was saturated. During a prolonged depolarization, the Ca2+ transient gradually declined. The time course of decline became faster when long depolarizing pulses were repeated, or when the temperature was increased. The Q10 for half duration of the Ca2+ transient evoked by prolonged depolarization was 2.2. A Ca2+ transient could be evoked in Ca2+-free Ringer solution containing EGTA. Formamide, which is known to abolish excitation-contraction coupling, also abolished the Ca2+ transient. During maintained depolarization, the time integral of the Ca2+ transient was larger for larger depolarizations, suggesting that the total amount of Ca2+ released was greater for the more intense depolarization. The decline of the Ca2+ transient during maintained depolarization is probably due to inactivation of excitation-contraction coupling rather than the depletion of intracellular Ca2+ stores. These findings support the view that in frog skeletal muscle fibres the increase in intracellular Ca2+, caused by membrane depolarization, is produced by the release of Ca2+ from intracellular stores and that any influx of Ca2+ from the external medium does not contribute appreciably to the aequorin-Ca2+ transient.
在注射了水母发光蛋白的青蛙缝匠肌纤维中，研究了由动作电位或去极化钳制脉冲诱发的细胞内Ca2+瞬变。随着温度升高，Ca2+瞬变的时间进程变短。在阿累尼乌斯图中，半上升时间和衰减时间常数在3至30摄氏度之间呈直线，Q10分别为2.5和2.3。在电压钳制下检查了Ca2+瞬变的电位依赖性。峰值光幅度在约+50 mV时达到平台期，表明Ca2+释放持续超过收缩饱和的电位水平。在长时间去极化期间，Ca2+瞬变逐渐下降。当重复长去极化脉冲或温度升高时，下降的时间进程变得更快。长时间去极化诱发的Ca2+瞬变半持续时间的Q10为2.2。在含有乙二醇双乙醚二胺四乙酸（EGTA）的无Ca2+林格氏液中可诱发Ca2+瞬变。已知能消除兴奋-收缩偶联的甲酰胺也消除了Ca2+瞬变。在持续去极化期间，去极化程度越大，Ca2+瞬变的时间积分越大，这表明更强的去极化释放的Ca2+总量更大。持续去极化期间Ca2+瞬变的下降可能是由于兴奋-收缩偶联的失活，而不是细胞内Ca2+储存的耗尽。这些发现支持这样一种观点，即在青蛙骨骼肌纤维中，膜去极化引起的细胞内Ca2+增加是由细胞内储存释放Ca2+产生的，并且从外部介质流入的任何Ca2+对水母发光蛋白-Ca2+瞬变的贡献不大。
