Effects of Na+ on Sugar and Amino Acid Transport in Striated Muscle*

Abstract

The effects of Na+ on sugar and amino acid transport are studied in the cut and intact rat diaphragm preparations and frog sartorius muscle. Amino acid transport is measured with the nonmetabolizable amino acid analogue [alpha]-amino-isobutyric acid (AIB); sugar transport is studied with 2-deoxyglucose and galactose. AIB is transported by an active carrier-mediated process and by diffusion, whereas 2-deoxyglucose is transported by the same nonactive carrier mediated system responsible for glucose movement. Galactose penetration, in tike absence of insulin, appears to be a process similar to diffusion. The results indicate that: (1) Na+ is necessary for the active transport of AIB and its stimulation by insulin; (2) sugar transport and its insulin stimulation is not dependent on Na+; (3) strophanthin K inhibits the amino acid transport system and does so independently from its inhibition of Na+ transport, and (4) the kinetics of AIB penetration in the absence of Na+ are those of a nonactive carrier-mediated mechanism similar to that involved in sugar transport. It is suggested that the active transport process consists of two components: a carrier system responsible for the structural specificity of the process, and a mechanism responsible for the linkage of metabolic energy and osmosis.