Changes in luminal pH caused by calcium release in sarcoplasmic reticulum vesicles
Changes in luminal pH caused by calcium release in sarcoplasmic reticulum vesicles
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DOI：
10.1016/s0006-3495(98)77786-0
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发表时间：
1998-01-01
影响因子：
3.4
通讯作者：
Hidalgo, C
中科院分区：
文献类型：
--
作者：
Kamp, F;Donoso, P;Hidalgo, C
肌浆网快速（毫秒）释放 Ca2+ 是肌肉收缩的重要步骤。为了在电学上补偿钙释放产生的电荷不足，需要其他离子的伴随通量。在这项研究中，我们研究了质子在钙释放过程中作为抗衡离子的可能参与。从兔快速骨骼肌中分离出的富含三联体的肌浆网囊泡，被动加载 1 mM CaCl2，并在停流荧光计中在 pCa = 5.0 和 pH = 7.0 时诱导释放。用捕获的荧光 pH 指示剂（吡喃）测量囊泡腔 pH 值的伴随变化。管腔的显着酸化（类似于 0.2 pH 单位）在与钙释放相同的时间尺度（t(1/2) = 0.75 s）内发生。使用 ATP 或 ATP 类似物 5'-腺苷酰亚胺二磷酸 (AMPPNP) 增强钙释放，可使酸化速度加快 20 倍以上。相反，当用含或不含 AMPPNP 的钙诱导的钙释放被 Mg2+ 阻断时，未观察到管腔酸化。在所有情况下，管腔酸化的速率常数与报告的钙释放速率常数值相对应。我们得出结论，质子通量占钙释放过程中必要电荷补偿的一部分（5-10%）。讨论了这些发现与肌肉细胞生理学的可能相关性。
Fast (milliseconds) Ca2+ release from sarcoplasmic reticulum is an essential step in muscle contraction. To electrically compensate the charge deficit generated by calcium release, concomitant fluxes of other ions are required. In this study we investigated the possible participation of protons as counterions during calcium release. Triad-enriched sarcoplasmic reticulum vesicles, isolated from rabbit fast skeletal muscle, were passively loaded with 1 mM CaCl2 and release was induced at pCa = 5.0 and pH = 7.0 in a stopped-flow fluorimeter. Accompanying changes in vesicular lumen pH were measured with a trapped fluorescent pH indicator (pyranin). Significant acidification (similar to 0.2 pH units) of the lumen occurred within the same time scale (t(1/2) = 0.75 s) as calcium release. Enhancing calcium release with ATP or the ATP analog 5'-adenylylimidodiphosphate (AMPPNP) produced >20-fold faster acidification rates. In contrast, when calcium release induced with calcium with or without AMPPNP was blocked by Mg2+, no acidification of the lumen was observed. In all cases, rate constants of luminal acidification corresponded with reported values of calcium release rate constants. We conclude that proton fluxes account for part (5-10%) of the necessary charge compensation during calcium release. The possible relevance of these findings to the physiology of muscle cells is discussed.