The Na +/Ca 2+ exchanger inhibitor KB-R7943 activates large-conductance Ca 2+-activated K + channels in endothelial and vascular smooth muscle cells

Abstract

The effect of the selective inhibitor of Na +/Ca 2+ exchanger (NCX), KB-R7943, on large-conductance Ca 2+-activated K + (BK Ca) channels was examined in cultured human umbilical vein endothelial cells (HUVECs) and freshly isolated mouse aortic smooth muscle cells (MASMCs). In voltage-clamped cells, KB-R7943 reversibly activated BK Ca currents in HUVECs and MASMCs. The EC 50 of KB-R7943 for BK Ca current activation in HUVECs was determined to be 6.78 ± 0.7 μM. In inside-out and outside-out patches, KB-R7943 markedly increased BK Ca channel activity and slightly decreased single channel current amplitudes. In inside-out patches, KB-R7943 shifted the relationship between [Ca 2+] i and open probability ( P o) to the left; the [Ca 2+] i required to evoke half-maximal activation changed from 1220 ± 68 nM (in the absence of KB-R7943) to 620 ± 199 nM (in the presence of 10 μM KB-R7943). In addition, KB-R7943 shifted the relationship between membrane potential and P o to the left; the membrane potential to evoke half-maximal activation changed from 76.86 ± 1.09 mV (in the absence of KB-R7943) to 49.62 ± 2.55 mV (in the presence of 10 μM KB-R7943). In conclusion, KB-R7943 was found to act as a potent BK Ca channel activator, which increases the sensitivity of BK Ca channels to cytosolic free Ca 2+ and membrane potential, and thereby BK Ca channel activity. These results should be considered when KB-R7943 is used as NCX blocker.