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

¹ Cardiovascular Research Institute and Departments of Medicine and Physiology, University of California School of Medicine, San Francisco, California

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 -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 -ketoglutarate, 33% with fructose-1,6-diphosphate, and 51% with pyruvate than with glucose. Sodium gain was accelerated by 8%, 16%, and 49% with -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.