Chelation of intracellular calcium blocks insulin action in the adipocyte.
The hypothesis that intracellular Ca2+ is an essential component of the intracellular mechanism of insulin action in the adipocyte was evaluated. Cells were loaded with the Ca2+ chelator quin-2, by preincubating them with quin-2 AM, the tetrakis(acetoxymethyl) ester of quin-2. Quin-2 loading inhibited insulin-stimulated glucose transport (IC50, 26 microM quin-2 AM) without affecting basal activity. The ability of insulin to stimulate glucose uptake in quin-2-loaded cells could be partially restored by preincubating cells with buffer supplemented with 1.2 mM CaCl2 and the Ca2+ ionophore A23187. These conditions had no effect on basal activity and omission of CaCl2 from the buffer prevented the restoration of insulin-stimulated glucose uptake by A23187. Quin-2 loading also inhibited insulin-stimulated glucose oxidation (IC50, 11 microM quin-2 AM) and the ability of insulin to inhibit cAMP-stimulated lipolysis (IC50, 78 microM quin-2 AM), without affecting their basal activities. Incubation of cells with 100 microM quin-2 or quin-2 AM had no effect on intracellular ATP concentration or the specific binding of 125I-labeled insulin to adipocytes. These findings suggest that intracellular Ca2+ is an essential component in the coupling of the insulin-activated receptor complex to cellular physiological/metabolic machinery. Furthermore, differing quin-2 AM dose-response profiles suggest the presence of dual Ca2+-dependent pathways in the adipocyte. One involves insulin stimulation of glucose transport and oxidation, whereas the other involves the antilipolytic action of insulin.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains
D000634:Aminoquinolines; D002614:Chelating Agents; D006601:Hexoses; D000001:Calcimycin; D000255:Adenosine Triphosphate; D005947:Glucose; C035739:Quin2; D002118:Calcium