On the instability of K+ influx in erythrocytes of the rainbow trout, Salmo gairdneri, and the role of catecholamine hormones in maintaining in vivo influx activity.

The rate of K+ influx in washed trout erythrocytes was not stable and declined by 60% over a 6 h period, but decreased only slowly thereafter. During this initial period the cells shrank, although [K+]i was maintained constant. Both ouabain-sensitive and furosemide-sensitive K+ influx were reduced by approximately equal amounts. Extensive modification of the saline composition produced no diminution of the loss of K+ influx activity, making it unlikely that the response was due to deficiencies in saline composition. The rate of K+ influx in unwashed cells was affected only slightly by noradrenaline and adrenaline. By contrast, K+ influx in cells which had been washed and incubated overnight before assay was stimulated 100-250% by these hormones. Half-maximal stimulation was at 2 X 10(-6) and 8 X 10(-6) M respectively. Replacement of plasma by a saline containing 5 X 10(-6) M adrenaline and noradrenaline resulted in high and stable K+ influx rates over a 6 h period. These results support the hypothesis that K+ influx in erythrocytes of freshly drawn blood is high as a result of stimulation by catecholamine hormones. Removal of the normal hormonal milieu, by washing of the cells, results in the rapid loss of K+ influx activity.