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KMID : 0811720070110000086
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Korean Journal of Physiology & Pharmacology
2007 Volume.11 No. 0 p.86 ~ p.0
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Activation of Large-Conductance Ca2+-Activated K+ Channels by KB-R7943
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Liang Guo Hua
Kim Ji-Ae
Choi Shin-Kyu
Suh Suk-Hyo
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Abstract
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We examined the effect of the selective inhibitor of Na+/Ca2+ exchanger (NCX), KB-R7943, on large-conductance Ca2+-activated K+ (BKCa) channels in cultured human umbilical vein endothelial cells (HUVECs) and freshly isolated mouse aortic smooth muscle cells (MASMCs). In whole-cell clamped cells, KB-R7943 reversibly activated BKCa currents in HUVECs and MASMCs. Furthermore, when intracellular Ca2+ was strongly buffered by 12 mM BAPTA in the pipette solution or NCX was inhibited by the replacement of external Na+ by NMDG+, BKCa currents were activated by KB-R7943. The EC50 for BKCa currents activation was calculated as 6.78±0.7μM. In inside-out and outside-out patches, KB-R7943 markedly increased the open probability of BKCa channels and slightly decreased single channel current amplitudes. In inside-out patches, KB-R7943 shifted the relationship between [Ca2+]i and open probability (Po) shifted to the left: the [Ca2+]i to evoke a half maximal activation was changed from 1220±70 nM (in the absence of KB-R7943) to 620±200 nM (in the presence of 10μM KB-R7943). In addition, the relationship between membrane potential and Po shifted to the left by KB-R7943: the membrane potential to evoke a half maximal activation was changed from 76.86±1.09 mV (in the absence of B-R7943) to 49.62±2.55 mV (in the presence of 10μM KB-R7943). In conclusion, KB-R7943 acts as a potent BKCa channel activator; it increases the sensitivity of BKCa channels to cytosolic free Ca2+ and membrane potential and thereby BKCa channel Po. These results should be considered when KB-R7943 is used as NCX blocker.
We examined the effect of the selective inhibitor of Na+/Ca2+ exchanger (NCX), KB-R7943, on large-conductance Ca2+-activated K+ (BKCa) channels in cultured human umbilical vein endothelial cells (HUVECs) and freshly isolated mouse aortic smooth muscle cells (MASMCs). In whole-cell clamped cells, KB-R7943 reversibly activated BKCa currents in HUVECs and MASMCs. Furthermore, when intracellular Ca2+ was strongly buffered by 12 mM BAPTA in the pipette solution or NCX was inhibited by the replacement of external Na+ by NMDG+, BKCa currents were activated by KB-R7943. The EC50 for BKCa currents activation was calculated as 6.78±0.7μM. In inside-out and outside-out patches, KB-R7943 markedly increased the open probability of BKCa channels and slightly decreased single channel current amplitudes. In inside-out patches, KB-R7943 shifted the relationship between [Ca2+]i and open probability (Po) shifted to the left: the [Ca2+]i to evoke a half maximal activation was changed from 1220±70 nM (in the absence of KB-R7943) to 620±200 nM (in the presence of 10μM KB-R7943). In addition, the relationship between membrane potential and Po shifted to the left by KB-R7943: the membrane potential to evoke a half maximal activation was changed from 76.86±1.09 mV (in the absence of B-R7943) to 49.62±2.55 mV (in the presence of 10μM KB-R7943). In conclusion, KB-R7943 acts as a potent BKCa channel activator; it increases the sensitivity of BKCa channels to cytosolic free Ca2+ and membrane potential and thereby BKCa channel Po. These results should be considered when KB-R7943 is used as NCX blocker.
Source: Korean Journal of Physiology & Pharmacology.2007 Oct;11(Suppl II):S81-S81
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KEYWORD
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KB-R7943, Activation, Large conductance Ca2+-activated K+ channel, HUVEC
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