Stimulation of large-conductance Ca²⁺-activated K⁺ channels by the Na⁺/Ca²⁺ exchanger inhibitor dichlorobenzamil in cultured human umbilical vein endothelial cells and mouse aortic smooth muscle cells

We investigated the effects of the selective inhibitor of Na ⁺/Ca²⁺ exchanger (NCX), 2′,4′- and 3′,4′-dichlorobenzamil (DCB), on large-conductance Ca ²⁺-activated K⁺ (BK_Ca) channels in cultured human umbilical vein endothelial cells (HUVECs) and fresh isolated mouse aortic smooth muscle cells (MASMCs) using the patch clamp techniques. Both kinds of DCB reversibly activated BK_Ca currents in whole-cell clamped HUVECs or MASMCs. The EC₅₀ of 2′,4′-DCB for BK_Ca current activation in HUVECs was 2.64 ± 0.10 μM. In inside-out and outside-out patches, 2′,4′-DCB remarkably increased BK_Ca channels activity. 2′,4′-DCB increased open frequency, but had no significant effect on mean open time. In inside-out patches, 2′,4′-DCB shifted the relationship curve between [Ca ²⁺]_i and open probability (NP_o) to the left; the [Ca²⁺]_i required to evoke half-maximal activation changed from 1087.45 ± 142.91 nM to 500.24 ± 66.83 nM by 10 μM 2′,4′-DCB. In addition, 2′,4′-DCB shifted the relationship curve between membrane potential and NP_o to the left; the membrane potential to evoke half-maximal activation changed from 81.1 ± 2.4 to 64.7 ± 3.1 mV by 10 μM 2′,4′-DCB. 3′,4′-DCB also increased BK_Ca channels activity. There was no significant difference in the effect of DCB on BK_Ca channels between both excised patches. These results suggested that 2′,4′- and 3′,4′-DCB activate BK_Ca channels activity in HUVECs and MASMCs by increasing the sensitivity of BK_Ca channels to cytosolic free Ca²⁺ and membrane potential. Our report would provide a consideration if they are used as NCX blocker in vascular endothelial cells or smooth muscle cells.