The relationship between the transport of glucose and cations across cell membranes in isolated tissues. XI. The effect of vanadate on 45Ca-efflux and sugar transport in adipose tissue and skeletal muscle.

(1) The effects of vanadate of hexose transport, 45Ca-exchange and (Na+, K+)-contents have been characterized in isolated adipose tissue and skeletal muscles of the rat. (2) In whole epididymal fat pads, vanadate (0.5-5.0 mM) markedly stimulated the uptake of 2-deoxy[14C]glucose as well as the efflux of 3-O-[14C]methylglucose. (3) Within the same concentration range, vanadate induced an early increase in 45Ca-washout from preloaded fat pads. The maximum increases in the fractional losses of 3-O-[14C]methylglucose and 45Ca were significantly correlated (P less than 0.001, r = 0.98). (4) In extensor digitorum longus and soleus muscles, vanadate (0.5-5.0 mM) stimulated the efflux of 3-O-[14C]methylglucose and this effect was preceded by rise in the washout of 45Ca. The maximum increases in the fractional losses pf 3-O-[14C]methylglucose and 45Ca were significantly correlated (P less than 0.005, r = 0.98). (5) In extensor digitorum longus and soleus muscles, vanadate increased K+-contents and decreased Na+ contents. (6) The stimulation of 45Ca-washout presumably reflects an increase in the cytoplasmic Ca2+ level, brought about by an inhibitory effect of vanadate on the Ca2+-sensitive ATPase of the sarcoplasmic or the endoplasmic reticulum. As demonstrated for most other insulin-like agents (Sørensen, S.S., Christensen, F. and Clausen, T. (1980) Biochim. Biophys. Acta 602, 433-445), the stimulating effect of vanadate on glucose transport appears to be associated with or mediated by a rise in the cytoplasmic Ca2+ level.