Inhibition of the cardiac ATP-dependent potassium current by KB-R7943

KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) was developed as a specific inhibitor of the sarcolemmal sodium-calcium exchanger (NCX) with potential experimental and therapeutic use. However, in cardiomyocytes KB-R7943 also effectively blocks several K+ currents including the delayed rectifier, IKr, and background inward rectifier, IK1. In the present study we analyze the effects of KB-R7943 on the ATP-dependent potassium current (IKATP) recorded by whole-cell patch-clamp in ventricular cardiomyocytes from a mammal (mouse) and a fish (crucian carp). IKATP was induced by external application of a mitochondrial uncoupler CCCP (3 × 10− 7 M) and internal perfusion of the cell with ATP-free pipette solution. A weakly inwardly rectifying current with a large outward component, recorded in the presence of CCCP, was blocked with 10− 5 M glibenclamide by 56.1 ± 4.6% and 56.9 ± 3.6% in crucian carp and mouse ventricular myocytes, respectively. In fish cardiomyocytes IKATP was blocked by KB-R7943 with an IC50 value of 3.14 × 10− 7 M, while in mammalian cells IC50 was 2.8 × 10− 6 M (P < 0.05). 10− 5 M KB-R7943 inhibited CCCP-induced IKATP by 99.9 ± 0.13% and 97.5 ± 1.2% in crucian carp and mouse ventricular myocytes, respectively. In crucian carp the IKATP is about an order of magnitude more sensitive to KB-R7943 than the background IK1, but in mammals IKATP and IK1 are almost equally sensitive to KB-R7943. Therefore, the ability of KB-R7943 to block IKATP should be taken into account together with INCX inhibition when investigating possible cardioprotective effects of this compound.