Oxidants and regulation of K+-Cl- cotransport in equine red blood cells

The effect of oxidants on K+-Cl- cotransport (KCC) was investigated in equi ne red blood cells. Carbon monoxide mimicked O-2. The substituted benzaldeh yde, 12C79 (5 mM), markedly increased O-2 affinity. In N-2, however, O-2 sa turation was low (<10%) but KCC remained active. Nitrite (NO2-) oxidized he me to methemoglobin (metHb). High concentrations of NO2- (1 and 5 mM vs. 0. 5 mM) increased KCC activity above control levels; it became O-2 independen t but remained sensitive to other stimuli. 1-Chloro-2,4-dinitrobenzene (1-3 mM) depleted reduced glutathione (GSH). Prolonged exposure (60-120 min, 1 mM) or high concentrations (3 mM) stimulated an O-2-independent KCC activit y; short exposures and low concentrations (30 min, 0.5 or 1 mM) did not. Th e effect of these manipulations was correlated with changes in GSH and metH b concentrations. An oxy conformation of Hb was necessary for KCC activatio n. An increase in its activity over the level found in oxygenated control c ells required both accumulation of metHb and depletion of GSH. Findings are relevant to understanding the physiology and pathology of regulation of KC C.