PUB - Publikationen an der Universität Bielefeld

The effects of isoliquiritigenin on force of contraction (Fc), L-type Ca2+ current (ICa) and intracellular Ca2+ concentration ([Ca2+]i) were investigated in rat ventricular heart muscle. Isoliquiritigenin increased Fc and ICa and, after longer exposure times, resting tension and [Ca2+]i. The effect of isoliquiritigenin (100 μM) on ICa was diminished by Rp-cAMPS (30 μM). 1H-[1,2,4]oxa-diazolo[4,3-a]quinoxalin-1-one (50 μM) did not influence the effects of isoliquiritigenin on Fc and ICa. The positive inotropic effects of isoprenaline and forskolin, but not of 3-isobutyl-1-methylxanthine, were potentiated by isoliquiritigenin (100 μM). In the presence of milrinone (10 μM), no further effects of isoliquiritigenin (100 μM) on Fc and ICa were observed. It is suggested that the increase in Fc and ICa by isoliquiritigenin is due to an accumulation of cyclic AMP. These effects are probably unrelated to an effect of the drug on soluble guanylyl cyclase, as reported for smooth muscle, but rather due to a direct inhibition of phosphodiesterase III activity.