We examined the effects of the mitochondrial Ca2+-activated K+ (mitoBK(Ca)) channel activator NS 1619 on L-type Ca2+ channels in rat ventricular myocytes. NS 1619 inhibited the Ca2+ current in a dose-dependent manner. NS 1619 shifted the activation curve to more positive potentials, but did not have a significant effect on the inactivation curve. Pretreatment with inhibitors of membrane BKCa channel, mitoBK(Ca) channel, protein kinase C, protein kinase A, and protein kinase G had little effect on the Ca (2+) current and did not alter the inhibitory effect of NS 1619 significantly. The application of additional NS 1619 in the presence of isoproterenol, a selective P-adrenoreceptor agonist, reduced the Ca (2+) current to approximately the same level as a single application of NS 1619. In conclusion, our results suggest that NS 1619 inhibits the Ca (2+) current independent of the mitoBKCa channel and protein kinases. Since NS 1619 is widely used to study mitoBK(Ca) channel function, it is essential to verify these unexpected effects of NS 1619 before experimental data can be interpreted accurately. (c) 2007 Elsevier Inc. All rights reserved.