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  • Title: The Na(+)/Ca(2+) exchanger inhibitor KB-R7943 activates large-conductance Ca(2+)-activated K(+) channels in endothelial and vascular smooth muscle cells.
    Author: Liang GH, Kim JA, Seol GH, Choi S, Suh SH.
    Journal: Eur J Pharmacol; 2008 Mar 17; 582(1-3):35-41. PubMed ID: 18237728.
    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 microM. 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 microM 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 microM 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.
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