Swelling, NEM, and A23187 activate Cl(-)-dependent K+ transport in high-K+ sheep red cells.

Abstract

In low K+ (LK) sheep red cells a significant fraction of the total ouabain-resistant (OR) K+ flux is inhibited when Cl- is replaced by other anions of the Hofmeister series except Br- (Cl(-)-dependent K+ flux). In contrast, high K+ (HK) sheep red cells in isosmotic media did not possess any significant OR Cl(-)-dependent K+ flux when Cl- was replaced by NO3- or I-. However, exposure to hyposmotic solutions, treatment with the sulfhydryl (SH) group reagent N-ethylmaleimide (NEM) or with the bivalent metal ion (Me2+) ionophore A23187 in absence of external Me2+ caused a significant activation of Cl(-)-dependent K+ transport as measured with Rb+ as K+ congener. There was no Cl(-)-dependent Rb+ flux in A23187-treated cells when Mn2+, Mg2+, and Ca2+ were present at 1 mM concentrations, suggesting that cellular accumulation of these Me2+ is inhibitory. Similar to LK red cells, HK red cells failed to respond to A23187 when pretreated with NEM supporting the hypothesis proposed recently (Lauf, P. K. J. Membr. Biol. 88: 1-13, 1985) of a common mechanism of Cl(-)-dependent K+ transport activation. The magnitudes of the Cl(-)-dependent Rb+ fluxes in HK cells were much smaller than those elicited by identical treatments in LK red cells, and the effect of all interventions was not due to the presence of reticulocytes known to possess Cl(-)-dependent K+ transport.(ABSTRACT TRUNCATED AT 250 WORDS)