The relationship between the transport of glucose and cations across cell membranes in isolated tissues. X. Effect of glucose transport stimuli on the efflux of isotopically labelled calcium and 3-O-methylglucose from soleus muscles and epididymal fat pads of the rat.

(1) The relationship between Ca2+ and sugar transport has been studied by comparing the washout of 45Ca and 3-O-[14C]methylglucose from preloaded isolated rat soleus muscles and whole epididymal fat pads. (2) In soleus muscle, nine different agents with well established stimulating effects on glucose transport were all found to produce a marked increase in 3-O-[14C]methylglucose washout, which in each instance was preceded by or coincided with a rise in the washout of 45Ca. (3) Trypsin, 2,4-dinitrophenol, p-chloromercuriphenylsulfonic acid, H2O2 and hyperosmolarity all produced dose-dependent stimulation of the washout of 45Ca and 3-O-[3H]methylglucose. Regression analysis showed a highly significant correlation between the increases in the two parameters (P < 0.001). (4) Depolarization and Na+ influx induced by veratrine were found to be associated with a marked rise in 45Ca release followed by stimulation of 3-O-[14C]methylglucose washout. (5) In epididymal fat pads, six different agents known to stimulate glucose transport were found to produce a highly significant (P < 0.001) increase in the washout of 45Ca and 3-O-[14C]methylglucose. (6) It is concluded that in the major targets for insulin action, activation of the glucose transport system can be elicited by a rise in cytoplasmic Ca2+ concentration brought about by mobilization of Ca2+ from endogenous cellular pools.