Insulin action in isolated fat cells. I. Effects of divalent cations on the stimulation by insulin of glucose uptake.

The effects of divalent cations, in particular Ca2+ and Mg2+, on glucose uptake by rat isolated fat cells in the presence and absence of insulin have been studied. EDTA (disodium salt) was used to deplete the bovine serum albumin present in the incubation medium of endogenous divalent cations prior to incubation with the cells, but was not present in the incubation medium during the incubation of the cells. The removal of Ca2+ and Mg2+ from the incubation medium did not affect the basal glucose uptake, but abolished the ability of insulin to stimulate glucose uptake by the cells. Addition of 25 microM MgCl2 or CaCl2 to the incubation medium restored a significant insulin stimulation, and this stimulation was maximal when 0.1 mM MgCl2 or CaCl2 had been added. SrCl2 and BaCl2 were also effective in restoring the insulin stimulation, but did not substitute fully for Ca2+ and Mg2+ in the incubation medium. Possible explanation for these observations are discussed.