Potassium channels in primary cultures of seawater fish gill cells. II. Channel activation by hypotonic shock

Previous studies performed on apical membranes of seawater fish gills in primary culture have demonstrated the existence of stretch-activated K+ channels with a conductance of 122 pS. The present report examines the involvement of K+ channels in ion transport mechanisms and cell swelling. In the whole cell patch-clamp configuration, K+ currents were produced by exposing cells to a hypotonic solution or to 1 muM ionomycin. These K+ currents were inhibited by the addition of quinidine and charybdotoxin to the bath solution. Isotopic efflux measurements were performed on cells grown on permeable supports using Rb-86(+) as a tracer to indicate potassium movements. Apical and basolateral membrane Rb-86 effluxes were stimulated by the exposure of cells to a hypotonic medium. During the hypotonic shock, the stimulation of Rb-86 efflux on the apical side of the monolayer was inhibited by 500 muM quinidine or 100 muM gadolinium but was insensitive to scorpion venom [Leirus quinquestriatus hebraeus (LQH)]. An increased Rb-86 efflux across the basolateral membrane was also reduced by the addition of quinidine and LQH venom but was not modified by gadolinium. Moreover, basolateral and apical membrane Rb-86 effluxes were not modified by bumetanide or thapsigargin. There is convincing evidence for two different populations of K+ channels activated by hypotonic shock. These populations can be separated according to their cellular localization (apical or basolateral membrane) and as a function of their kinetic behavior and pharmacology.