Carbohydrate metabolism and electrolyte content of rabbit diaphragm in vitro: effect of Na pyruvate.

Abstract

Effects of carbohydrate intermediates on conservation of electrolyte gradients in muscle were studied by incubating segments of rabbit diaphragm in substrate-free media or media containing either 5.6 mm glucose, fructose-1, 6-diphosphate, pyruvate, or α-ketoglutarate. These were without effect on Na+-K+ gradient in glycogen-rich diaphragm. Loss of K+ and gain of Na+ were slightly greater in pyruvate- than in glucose-fortified media. Glycogen-poor diaphragm, however, lost considerably less K+ and gained less Na+ in glucose than in substrate-free media. Other substrates did not reduce decay of electrolyte gradients. Loss of K+ was 19% greater with α-ketoglutarate, 33% with fructose-1,6-diphosphate, and 51% with pyruvate than with glucose. Sodium gain was accelerated by 8%, 16%, and 49% with α-ketoglutarate, fructose-1,6-diphosphate, and pyruvate, respectively. Only pyruvate facilitated chloride accumulation in muscle. Although the ability of glucose to decelerate loss of K+ and gain of Na+ in glycogen-poor diaphragm agrees with the hypothesis that Na+-K+ transport is ATP dependent in muscle, inhibitory effects of pyruvate and fructose-1,6-diphosphate remain to be explained.