Activation of K-Cl cotransport by mild warming in guinea pig red cells

Unidirectional, ouabain-insensitive K+ influx rose steeply with warming at temperatures above 37 degreesC in guinea pig erythrocytes incubated in isotonic medium. The only component of ouabain-insensitive K+ influx to show the same steep rise was K-Cl cotransport (Q10 of 10 between 37 and 41 degrees C); Na-K-Cl cotransport remained constant or declined and residual K+ influx in hypertonic medium with ouabain and bumetanide rose only gradually. Similar results were obtained for unidirectional K+ efflux. Thermal activation of K-Cl cotransport-mediated K+ influx was fully dependent on the presence of chloride in the medium; none occurred with nitrate replacing chloride. The increase of K+ influx through K-Cl cotransport from 37 to 41 degrees C was blocked by calyculin A, a phosphatase inhibitor. The Q10 of K-Cl cotransport fully activated by hydroxylamine and hypotonicity was about 2. The time course of K+ entry showed an immediate transition to a higher rate when cells were instantly warmed from 37 to 41 degrees C, but there was a 7-min time lag in returning to a lower rate when cells were cooled from 41 to 37 degrees C. These results indicate that the steepness of the response of K-Cl cotransport to mild warming is due to altered regulation of the transporter. Total unidirectional K+ influx was equal to total unidirectional K+ efflux at 37-45 degrees C, but K+ influx exceeded K+ efflux at 41 degrees C when K-Cl cotransport was inhibited by calyculin or prevented by hypertonic incubation. The net loss of K+ that results from the thermal activation of isosomotic K-Cl cotransport reported here would offset a tendency for cell swelling that could arise with warming through an imbalance of pump and leak for Na+ or for K+.