Torres R J, Subramanyam M, Altenberg G A, Reuss L
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77555-0641, USA.
J Gen Physiol. 1997 Jan;109(1):61-72. doi: 10.1085/jgp.109.1.61.
Necturus gallbladder epithelial cells bathed in 10 mM HCO3/1% CO2 display sizable basolateral membrane conductances for Cl- (GClb) and K+ (GKb). Lowering the osmolality of the apical bathing solution hyperpolarized both apical and basolateral membranes and increased the K+/Cl- selectivity of the basolateral membrane. Hyperosmotic solutions had the opposite effects. Intracellular free-calcium concentration ([Ca2+]i) increased transiently during hyposmotic swelling (peak at approximately 30 s, return to baseline within approximately 90 s), but chelation of cell Ca2+ did not prevent the membrane hyperpolarization elicited by the hyposmotic solution. Cable analysis experiments showed that the electrical resistance of the basolateral membrane decreased during hyposmotic swelling and increased during hyperosmotic shrinkage, whereas the apical membrane resistance was unchanged in hyposmotic solution and decreased in hyperosmotic solution. We assessed changes in cell volume in the epithelium by measuring changes in the intracellular concentration of an impermeant cation (tetramethylammonium), and in isolated polarized cells measuring changes in intracellular calcein fluorescence, and observed that these epithelial cells do not undergo measurable volume regulation over 10-12 min after osmotic swelling. Depolarization of the basolateral membrane voltage (Vcs) produced a significant increase in the change in Vcs elicited by lowering basolateral solution [Cl-], whereas hyperpolarization of Vcs had the opposite effect. These results suggest that: (a) Hyposmotic swelling increases GKb and decreases GClb. These two effects appear to be linked, i.e., the increase in GKb produces membrane hyperpolarization, which in turn reduces GClb. (b) Hyperosmotic shrinkage has the opposite effects on GKb and GClb. (c) Cell swelling causes a transient increase in [Ca2+]i, but this response may not be necessary for the increase in GKb during cell swelling.
置于含10 mM HCO3/1% CO2的溶液中的美西螈胆囊上皮细胞，其基底外侧膜对Cl-（GClb）和K+（GKb）具有可观的电导。降低顶端浴液的渗透压会使顶端和基底外侧膜均发生超极化，并增加基底外侧膜的K+/Cl-选择性。高渗溶液则产生相反的效果。在低渗肿胀过程中，细胞内游离钙浓度（[Ca2+]i）短暂升高（约30秒达到峰值，约90秒内恢复至基线），但细胞内Ca2+的螯合并不能阻止低渗溶液引起的膜超极化。电缆分析实验表明，在低渗肿胀过程中基底外侧膜的电阻降低，在高渗收缩过程中增加，而顶端膜电阻在低渗溶液中不变，在高渗溶液中降低。我们通过测量非渗透性阳离子（四甲基铵）细胞内浓度的变化来评估上皮细胞的体积变化，并在分离的极化细胞中测量细胞内钙黄绿素荧光的变化，观察到这些上皮细胞在渗透性肿胀后10 - 12分钟内未发生可测量的体积调节。基底外侧膜电压（Vcs）的去极化会使降低基底外侧溶液[Cl-]所引起的Vcs变化显著增加，而Vcs的超极化则产生相反的效果。这些结果表明：（a）低渗肿胀会增加GKb并降低GClb。这两种效应似乎相互关联，即GKb的增加导致膜超极化，进而降低GClb。（b）高渗收缩对GKb和GClb产生相反的影响。（c）细胞肿胀会导致[Ca2+]i短暂升高，但这种反应对于细胞肿胀期间GKb的增加可能并非必要。
