McCarty N A, O'Neil R G
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77030.
J Membr Biol. 1991 Aug;123(2):149-60. doi: 10.1007/BF01998085.
The mechanism of Ca(2+)-dependent control of hypotonic cell volume regulation was investigated in the isolated, nonperfused renal proximal straight tubule. When proximal tubules were exposed to hypotonic solution with 1 mM Ca2+, cells swelled rapidly and then underwent regulatory volume decrease (RVD). This treatment resulted in an increase in intracellular free calcium concentration ([Ca2+]i) by a mechanism that had two phases: the first was a transient increase from baseline (136 nM) to a peak (413 nM) that occurred in the first 15-20 sec, but was followed by a rapid decay toward the pre-swelling levels. The second phase was characterized by a sustained elevation of [Ca2+]i above the baseline (269 nM), which was maintained over several minutes. The dependence of these two phases on extracellular Ca2+ was determined. Reduction of bath [Ca2+] to 10 or 1 microM partially diminished the transient phase, but abolished the sustained phase completely, such that [Ca2+]i fell below the baseline levels during RVD. It was concluded that the transient increase resulted predominantly from swelling-activated release of intracellular Ca2+ stores and that the sustained phase was due to swelling-activated Ca2+ entry across the plasma membrane. Ca2+ entry probably also contributed to the transient increase in [Ca2+]i. The time dependence of swelling-activated Ca2+ entry was also investigated, since it was previously shown that RVD was characterized by a "calcium window" period (less than 60 sec), during which extracellular Ca2+ was required. Outside of this time period, RVD would inactivate and could not be reactivated by subsequent addition of Ca2+. It was found that the Ca2+ permeability did not inactivate over several minutes, indicating that the temporal dependence of RVD on extracellular Ca2+ is not due to the transient activation of a Ca2+ entry pathway.
在分离的、非灌注的肾近端直小管中研究了钙离子依赖性调节低渗细胞容积的机制。当近端小管暴露于含1 mM钙离子的低渗溶液中时，细胞迅速肿胀，随后经历调节性容积减小（RVD）。这种处理通过一种有两个阶段的机制导致细胞内游离钙浓度（[Ca2+]i）升高：第一阶段是在最初的15 - 20秒内从基线水平（136 nM）短暂升高至峰值（413 nM），但随后迅速下降至肿胀前水平。第二阶段的特征是[Ca2+]i持续高于基线水平（269 nM），并维持数分钟。确定了这两个阶段对细胞外钙离子的依赖性。将浴液中[Ca2+]降低至10或1 μM可部分减弱短暂阶段，但完全消除持续阶段，使得在RVD期间[Ca2+]i降至基线水平以下。得出的结论是，短暂升高主要源于肿胀激活的细胞内钙储存释放，而持续阶段是由于肿胀激活的钙离子跨质膜内流。钙离子内流可能也促成了[Ca2+]i的短暂升高。还研究了肿胀激活的钙离子内流的时间依赖性，因为先前已表明RVD的特征是一个“钙窗”期（小于60秒），在此期间需要细胞外钙离子。在此时间段之外，RVD将失活，并且随后添加钙离子不能使其重新激活。发现钙离子通透性在数分钟内不会失活，这表明RVD对细胞外钙离子的时间依赖性不是由于钙离子内流途径的短暂激活。
