CALCIUM DEPLETION IN FROG-MUSCLE TUBULES - THE DECLINE OF CALCIUM CURRENT UNDER MAINTAINED DEPOLARIZATION
CALCIUM DEPLETION IN FROG-MUSCLE TUBULES - THE DECLINE OF CALCIUM CURRENT UNDER MAINTAINED DEPOLARIZATION
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DOI：
10.1113/jphysiol.1981.sp013623
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
PALADE, PT
中科院分区：
文献类型：
--
作者：
ALMERS, W;FINK, R;PALADE, PT
用电压钳技术研究了蛙骨骼肌纤维的钙电流。在维持几秒的膜去极化下，当[Ca 2 +]0 = 10 mM时，Ca 2+电流以0.2-2秒的时间常数下降。异丙基-α- [N-甲基-N-高藜芦基-γ-氨基丙基]-3，4，5-三甲氧基苯乙腈]、丁卡因和Ni 2+。当通过使膜电位为正、通过用药物阻断或通过用渗透性相对较低的Mn 2+取代Ca 2+来减小峰电流时，下降速率减小。当通过在相对负的膜电位下记录或通过用渗透性更强的离子Ba ~（2+）或Sr ~（2+）取代Ca ~（2+）来增加峰电流时，下降速率成比例地增加。显然，水流的大小决定了下降的速度。在等渗Ca 2+盐水中或当[Ca 2 +]0被有机阴离子苹果酸盐缓冲时，电流的下降大大减慢。电流的下降显然是由于细胞外室（可能是横小管）中的Ca 2+耗尽。在此基础上，对Ca 2+电流的衰减和恢复进行了分析，得出以下结论。Ca 2+电流几乎完全流过横小管的膜。在考虑到管状网络的弯曲度之后，横小管中Ca 2+的表观扩散系数为约2.6 × 104。10-6 cm ~ 2/s，比K ~+在横小管中的扩散系数小3倍，比Ca ~（2+）在游离溶液中的扩散系数小约3倍。横小管腔似乎没有在mM范围内具有大的Ca 2+缓冲能力。在[Ca 2 +]0 = 10 mM时，对于每个游离离子，小管腔结合少于0.6个可解离的Ca 2+离子。
Ca2+ currents in frog skeletal muscle fibers were studied with a voltage-clamp technique. Under membrane depolarization maintained for several s, Ca2+ current declined with time constants of 0.2-2 s when [Ca2+]0 = 10 mM. Ca2+ currents are diminished by nifedipine, D-600 [.alpha.-isopropyl-.alpha.-[N-methyl-N-homoveratryl-.gamma.-aminopropyl]-3,4,5-trimethoxyphenylacetonitrile], tetracaine and Ni2+. When peak current is diminished by making the membrane potential positive, by block with drugs or by substituting the relatively less permeant Mn2+ for Ca2+, the rate of decline is diminished. When peak current is increased by recording at relatively negative membrane potentials or by substituting for Ca2+ the more permeant ions Ba2+ or Sr2+, the rate of decline is increased in proportion. Evidently the size of the current determines the rate of decline. Decline of current is greatly slowed in isotonic Ca2+ saline or when the [Ca2+]0 is buffered by the organic anion malate. The decline of current apparently arises from Ca2+ depletion in an extracellular compartment, probably the transverse tubules. On this basis, an analysis of Ca2+ current decline and recovery leads to the following conclusions. Ca2+ current flows almost entirely across the membranes of the transverse tubules. After allowing for the tortuosity of the tubular network, the apparent diffusion coefficient for Ca2+ in the transverse tubules is about 2.6 .times. 10-6 cm2/s, 3 times less than the diffusion coefficient for K+ in the transverse tubules and about 3 times less than the diffusion coefficient for Ca2+ in free solution. The transverse tubule lumen does not appear to have a large Ca2+-buffering capacity in the mM range. At [Ca2+]0 = 10 mM the tubule lumen binds less than 0.6 dissociable Ca2+ ions for every free ion.