SWELLING-ACTIVATED K+ TRANSPORT VIA 2 FUNCTIONALLY DISTINCT PATHWAYS IN EEL ERYTHROCYTES

Following osmotic swelling, erythrocytes from the European eel, Anguil la an guilla, underwent a regulatory volume decrease. This was prevent ed by replacement of Na+ with K+ in the suspending medium, consistent with a role for the (normally outward) electrochemical K+ gradient in the volume-regulatory response. The effect of cell swelling on K+ tran sport in these cells was investigated using Rb-86(+) as a tracer for K +. Osmotic swelling resulted in an increase in ouabain-insensitive Ktransport that was highest for cells in Cl- and Br- media but which wa s also significant in I- and NO3- media. Treatment of eel erythrocytes suspended in isotonic Cl- or Br- (but not I- or NO3-) media with the sulfhydryl reagent N-ethylmaleimide (NEM) resulted in a large increase in K+ transport. A quantitative comparison of the pharmacological pro perties of the ''Cl--dependent'' NEM-activated pathway with those of t he ''Cl--independent'' pathway mediating swelling-activated K+ transpo rt in cells in Cl--free (NO3- containing) media showed there to be sig nificant differences between them. By contrast, the pharmacological pr operties of the Cl--independent swelling-activated K+ pathway were ind istinguishable from those of the pathway responsible for the swelling- activated transport of taurine, the major organic osmolyte in these ce lls. A pharmacological analysis of ouabain-insensitive K+ transport in cells swollen in a hypotonic Cl--containing medium showed there to be two components, one with the characteristics of the NEM-activated sys tem, the other showing the characteristics of the Cl--independent swel ling-activated pathway. The data are consistent with the presence of t wo functionally distinct swelling-activated K+ transport mechanisms in eel erythrocytes: a KCl cotransporter that is activated under isotoni c conditions by NEM and a Cl--independent, broad-specificity channel t hat accommodates a diverse range of organic and inorganic solutes.