Control of NADH ferricyanide reductase activity in the human erythrocyte by somatotrophin and insulin

Reduction of external ferricyanide by the human erythrocyte is significantly stimulated by insulin and somatotrophin at concentrations above physiological levels. Basal (in absence of hormones) and hormone-stimulated activities are attenuated in the presence of glycolytic inhibitors iodoacetate and vanadate indicating the requirement of glycolytic substrates for the reduction process and for the activation of cellular metabolism in response to the hormones. Sulfhydryl reagents like N-ethylmaleimide also attenuate the basal and hormone-stimulated activities and this effect was rationalized on the basis of action at SH sites which trigger responses to hormones. Stimulation of ferricyanide reduction by insulin and somatotrophin may be also the result of Na⁺/H⁺ antiport activation which may be prevented by amiloride. This suggests that Na⁺/H⁺ antiport is part of the membrane transduction system for insulin and somatotrophin in the human erythrocyte. These observations are a contribution to the study of plasma membrane oxidoreductase systems involved in physiological and metabolic functions of the cell.