CELL SWELLING ACTIVATES THE K- CONDUCTANCE OF THE BASOLATERAL MEMBRANE OF CELLS FROM A LEAKY EPITHELIUM( CONDUCTANCE AND INHIBITS THE CL)

Necturus gallbladder epithelial cells bathed in 10 mM HCO3/1% CO2 disp lay sizable basolateral membrane conductances for Cl- (G(Cl)(b)) and K + (G(K)(b)). Lowering the osmolality of the apical bathing solution hy perpolarized 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 ([C a2+](i)) increased transiently during hyposmotic swelling (peak at sim ilar to 30 s, return to baseline within similar to 90 s), but chelatio n of cell Ca2+ did not prevent the membrane hyperpolarization elicited by the hyposmotic solution. Cable analysis experiments showed that th e electrical resistance of the basolateral membrane decreased during h yposmotic swelling and increased during hyperosmotic shrinkage, wherea s the apical membrane resistance was unchanged in hyposmotic solution and decreased in hyperosmotic solution. We assessed changes in cell vo lume by measuring changes in the intracellular concentration of an imp ermeant cation (tetramethylammonium), and in isolated polarized cells measuring changes in intracellular calcein fluorescence, and observed that these epithelial cells do not undergo measurable volume regulatio n over 10-12 min after osmotic swelling. Depolarization of the basolat eral membrane voltage (V-c5) produced a significant increase in the ch ange in V-c5 elicited by lowering basolateral solution [Cl-], whereas hyperpolarization of Ti-c5 had the opposite effect. These results sugg est that: (a) produces membrane hyperpolarization, which in turn reduc es G(Cl)(b). (b) Hyperosmotic shrinkage has the opposite effects on G( K)(b) and G(Cl)(b). (c) Cell swelling causes a transient increase in [ Ca2+](i), but this response may not be necessary for the increase in G (K)(b) during cell swelling.