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 quill 2-AM, a cell pe rmeant 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 insul in on lipolysis due to dibutyryl cAMP (Bt(2)cAMP) in a dose-dependent manne r [H. Goko, A. Matsuoka, Diabetes Res. Clin. Prac. 19 (1993) 177-181] and v erapamil. a calcium antagonist, potentiates lipolysis due to Bt,cAMP. Like W-7: W-5 suppressed the antilipolytic action of insulin on lipolysis due to Bt,cAMP in a dose-dependent manner. However, when lipolysis was potentiate d with 3-isobutyryl-1-methylxanthine (IBMX), W-5 did not suppl-ess the anti lipolytic action of insulin. At the same time, like verapamil, W-5 also pot entiated lipolysis due to Bt(2)cAMP in a dose-dependent manner. Thus W-5 ha s the pharmaceutica effects of both W-7 and verapamil. The chelation of int racellular Ca2+ in adipocytes with quin 2-AM also produced a dose-dependent potentiation of lipolysis due to Bt,cAMP and suppression of the antilipoly tic action of insulin on lipolysis due to Bt,cAMP. These effects of quin 2- AM are the same as those of W-5. Therefore, our results suggest that the cy toplasmic Ca2+ plays a pivotal role in mediating the potentiation of lipoly sis and antilipolytic action of insulin when lipolysis is induced by Bt(2)c AMP in rat adipocytes and that W-5 appears to exert its pharmaceutical effe cts through the inhibition of intracellular calcium-dependent steps other t han calmodulin. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.