METHEMOGLOBIN FORMATION AND REDUCTION IN CANINE ERYTHROCYTES CHARACTERIZED BY INHERITED HIGH NA+-ATPASE, K+-ATPASE ACTIVITY WITH NORMAL AND HIGH GLUTATHIONE CONCENTRATIONS

The methemoglobin formation and methemoglobin reduction in canine erythrocytes characterized by inherited high potassium (K+) and normal reduced glutathione concentrations (HK-low GSH cells) were compared with those in canine erythrocytes with inherited high K+ and high GSH concentrations (HK-high GSH cells) and normal canine erythrocytes with low K+ and low (= normal) GSH concentrations (LK-low GSH cells). The rate of methemoglobin formation induced by sodium nitrite (NaNO2) was in the order; LK-low GSH > HK-low GSH > HK-high GSH cells, and the difference among groups was significant at 7 and 15 min. Methemoglobin reduction in a medium containing glucose occurred rapidly in both HK-high GSH and HK-low GSH cells, and the rate of reduction was 1.7-fold higher than in LK-low GSH cells. Accumulation of pyruvate equivalent to the amount of methemoglobin reduced indicated that methemoglobin was predominantly reduced by NADH-methemoglobin reductase coupled to glycolysis. HK-low GSH cells showed an increased glycolytic rate and high pyruvate kinase activity similar to the levels in HK-high GSH cells. It is therefore evident that HK-low GSH cells offer greater protection against oxidation of hemoglobin to methemoglobin than LK-low GSH cells because of the increased glycolytic rate in HK-low GSH cells attributable to high pyruvate kinase activity in these cells.