Possible involvement of alanine and pyruvate in the regulation of glucose transport in heart muscle cells

Abstract

In isolated rat heart muscle cells, addition of L-alanine (1.5 mmol/l) or of L-valine (3 mmol/l) resulted in either a ca 1.5- or 1.3-fold increase in glucose transport, resp. half-maximal stimulation was observed in the presence of L-alanine, but not of L-valine. within a physiological plasmatic range of concentrations. D-Alanine (1.5 mmol/l) was ineffective and the stimulating effect of L-alanine could be prevented by an excess of L-serine (15 30 mmol/l). L-Alanine produced an increase in 3-O-methyl-D-glucose transport V max (from 44.6 to 81.5 pmols −1 mg protein −1) without affecting the K m (12.2 in control vs 12.8 mmol/l in alanine-treated cells). Pyruvate (1.5 mmol/l) inhibited glucose transport by 20% and prevented the stimulating action of L-alanine (1.5 mmol/l). These results suggest that the effect of L-alanine in cardiac myocytes occurs through the interaction with an intracellular site and that both alanine and pyruvate may play a role in the regulation of glucose transport in these cells.