W-5 and quin 2-AM reverse the inhibitory effect of insulin on lipolysis due to dibutyryl cAMP.
The effects of W-5, a weak calmodulin antagonist, and quin 2-AM, a cell permeant calcium chelator, on lipolysis and antilipolytic activity of insulin were studied in isolated rat adipocytes. We have previously shown that W-7, a strong calmodulin antagonist, suppresses the inhibitory effect of insulin on lipolysis due to dibutyryl cAMP (Bt2cAMP) in a dose-dependent manner [H. Goko, A. Matsuoka, Diabetes Res. Clin. Prac. 19 (1993) 177-181] and verapamil, a calcium antagonist, potentiates lipolysis due to Bt2cAMP. Like W-7, W-5 suppressed the antilipolytic action of insulin on lipolysis due to Bt2cAMP in a dose-dependent manner. However, when lipolysis was potentiated with 3-isobutyryl-1-methylxanthine (IBMX), W-5 did not suppress the antilipolytic action of insulin. At the same time, like verapamil, W-5 also potentiated lipolysis due to Bt2cAMP in a dose-dependent manner. Thus W-5 has the pharmaceutical effects of both W-7 and verapamil. The chelation of intracellular Ca2+ in adipocytes with quin 2-AM also produced a dose-dependent potentiation of lipolysis due to Bt2cAMP and suppression of the antilipolytic action of insulin on lipolysis due to Bt2cAMP. These effects of quin 2-AM are the same as those of W-5. Therefore, our results suggest that the cytoplasmic Ca2+ plays a pivotal role in mediating the potentiation of lipolysis and antilipolytic action of insulin when lipolysis is induced by Bt2cAMP in rat adipocytes and that W-5 appears to exert its pharmaceutical effects through the inhibition of intracellular calcium-dependent steps other than calmodulin.
Department of Medical Technology, Kobe University School of Medicine, Japan.
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Goko
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Matsuoka
D017667:Adipocytes / Q000187:drug effects / Q000502:physiology*; D000634:Aminoquinolines / Q000494:pharmacology*; D000818:Animals; D003994:Bucladesine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004822:Epididymis; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects* / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides / Q000494:pharmacology*
D000634:Aminoquinolines; D002614:Chelating Agents; D007328:Insulin; D013449:Sulfonamides; D003994:Bucladesine; C034700:N-(6-aminohexyl)-1-naphthalenesulfonamide; C035738:Quin2-acetoxymethyl ester