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 pr imary culture have demonstrated the existence of stretch-activated K+ chann els with a conductance of 122 pS. The present report examines the involveme nt of K+ channels in ion transport mechanisms and cell swelling. In the who le cell patch-clamp configuration, K+ currents were produced by exposing ce lls to a hypotonic solution or to 1 muM ionomycin. These K+ currents were i nhibited by the addition of quinidine and charybdotoxin to the bath solutio n. 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 o f 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 [Lei rus quinquestriatus hebraeus (LQH)]. An increased Rb-86 efflux across the b asolateral membrane was also reduced by the addition of quinidine and LQH v enom but was not modified by gadolinium. Moreover, basolateral and apical m embrane Rb-86 effluxes were not modified by bumetanide or thapsigargin. The re is convincing evidence for two different populations of K+ channels acti vated by hypotonic shock. These populations can be separated according to t heir cellular localization (apical or basolateral membrane) and as a functi on of their kinetic behavior and pharmacology.