The Effect of Oxidative Metabolic Substrates on the Membrane Transport of Sugars and on the Action of Ouabain in Skeletal Muscle In Vitro

Abstract

Factors which modify sugar transport in muscle were studied by measuring the tissue–medium distribution of the nonmetabolized sugar 3-O-methyl-D-glucose in the rat diaphragm in vitro. Pyruvate, lactate, and β-hydroxybutyrate did not influence sugar transport. n-Octanoate usually stimulated sugar transport but under some conditions antagonized its stimulation by insulin; it also appeared to inhibit the Na⁺ pump. Succinate also antagonized stimulation of sugar transport by insulin. The effects of these two substrates resemble those of long-chain fatty acids. The inhibition of cation transport by 10⁻⁵ g/ml ouabain was not influenced by any of the above oxidative substrates or by insulin. In contrast, the effect of ouabain to increase sugar transport was much increased by the presence of insulin, and was also enhanced by the presence of glucose but not the other oxidative substrates, during a prior interval of incubation. In the combined presence of glucose and insulin internal K⁺ was elevated and internal Na⁺ decreased to a small but significant extent.