Hudson R L, Schultz S G
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
Proc Natl Acad Sci U S A. 1988 Jan;85(1):279-83. doi: 10.1073/pnas.85.1.279.
The addition of 10 mM glycine to a physiological saline bathing Ehrlich ascites tumor cells is followed by a slow increase in cell volume that plateaus between 15 and 30 min at a level approximately equal to 17% greater than the control volume; this increase is not observed when glycine is added to cells suspended in a Na+-free saline. The results of studies using the patch-clamp technique in the cell-attached mode indicate that, 0.5-3 min after the addition of glycine to the bathing solution, there is a marked increase in the activity of single channels, which is almost all instances were previously present and operant in the plasma membrane. Successfully excised patches of membrane that contained a channel stimulated by glycine fell into two categories. Some became inactive within 15 sec in spite of the fact that the G omega seal remained intact. Others persisted for the lifetime of the seal. All of the persistent channels had an 11-fold selectivity for Cl- over K+ and a conductance of 23 pS when bathed by symmetrical 150 mM KCl solutions. Although the ionic specificities of the other channels have not been identified, there is reason to suspect that they might be K+ channels whose activities are dependent on factors lost when the patch is excised. Swelling induced by exposing these cells to a 50% hypotonic perfusate stimulated the activities of Cl- channels whose properties closely resemble those stimulated by the addition of glycine to the perfusate, strongly suggesting that the glycine-induced stimulation of Cl- channel activity is part of a volume-regulatory response to cell swelling. If the increase in channel activity induced by the addition of glycine to the perfusate is indeed a response to cell swelling, then this perfusate is indeed a response to cell swelling, then this volume-regulatory response must be extremely sensitive inasmuch as it appears to be "triggered" by an average increase in cell volume that does not exceed 5%.
向 Ehrlich 腹水肿瘤细胞的生理盐水中添加 10 mM 甘氨酸后，细胞体积会缓慢增加，并在 15 至 30 分钟之间达到平稳状态，此时的体积比对照体积大约大 17%；当将甘氨酸添加到悬浮于无钠盐溶液中的细胞时，未观察到这种增加。采用膜片钳技术在细胞贴附模式下进行的研究结果表明，在向浴液中添加甘氨酸后 0.5 - 3 分钟，单通道活性显著增加，在几乎所有情况下，这些通道先前都存在于质膜中且有活性。成功切除的含有受甘氨酸刺激的通道的膜片分为两类。尽管 GΩ 封接保持完整，但有些在 15 秒内就失去活性。其他的则在封接的整个存续期内保持活性。当用对称的 150 mM KCl 溶液灌流时，所有持续存在的通道对 Cl⁻ 与 K⁺ 的选择性为 11 倍，电导为 23 pS。尽管其他通道的离子特异性尚未确定，但有理由怀疑它们可能是 K⁺ 通道，其活性依赖于膜片切除时丢失的因子。将这些细胞暴露于 50% 的低渗灌流液中诱导的肿胀刺激了 Cl⁻ 通道的活性，其特性与向灌流液中添加甘氨酸所刺激的特性极为相似，这强烈表明甘氨酸诱导的 Cl⁻ 通道活性刺激是对细胞肿胀的一种体积调节反应的一部分。如果向灌流液中添加甘氨酸所诱导的通道活性增加确实是对细胞肿胀的一种反应，那么这种体积调节反应必定极其敏感，因为它似乎是由细胞体积平均增加不超过 5% 所“触发”的。
