Insulin action in isolated fat cells. II. Effects of divalent cations on stimulation by insulin of protein synthesis, on inhibition of lipolysis by insulin, and on the binding of 125I-labelled insulin to isolated fat cells.
The effects of ommission of Ca2+ and Mg2+ from the incubation medium on three aspects of insulin action in isolated fat cells have been investigated. In the (Ca2+ + Mg2+)-free incubation medium incorporation of L-[14C]leucine into fat cell protein was reduced in the absence of insulin. Insulin stimulated L-[14C]leucine incorporation only in the presence of added CaCl2 or MgCl2. Incubation of the cells in the (Ca2+ + Mg2+)-free medium reduced but did not abolish the ability of adrenaline to stimulate lipolysis or the ability of insulin to inhibit the adrenaline-stimulated lipolysis. Specific binding of 125I-labelled insulin to the fat cells was reduced in the absence of Ca2+ and Mg2+ but was not abolished, even in the presence of EDTA. Ca2+ was routinely the most effective divalent cation in supporting these aspects of insulin action, but similar responses were obtained with Mg2+, Sr2+ and Ba2+. Since insulin still binds to the cells under conditions in which some of the cellular effects of the hormone are abolished, it is suggested that divalent cations may have a role, either direct or indirect, in the processes linking the insulin-insulin receptor complex to certain effector systems in the cells. It is tentatively suggested that this action occurs at the level of the fat cell plasma membrane.
D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007930:Leucine / Q000378:metabolism; D008053:Lipid Mobilization / Q000187:drug effects*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D014176:Protein Biosynthesis; D051381:Rats
D002413:Cations, Divalent; D007328:Insulin; D007930:Leucine; D008274:Magnesium; D002118:Calcium