The Na(+)/Ca(2+) exchanger inhibitor KB-R7943 activates large-conductance Ca(2+)-activated K(+) channels in endothelial and vascular smooth muscle cells.
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.
Liang
Guo Hua
GH
Department of Physiology and Medical Research Institute, College of Medicine, Ewha Womans University, Seoul, Republic of Korea.
Kim
Ji Aee
JA
Seol
Geun Hee
GH
Choi
Shinkyu
S
Suh
Suk Hyo
SH
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D014471:Umbilical Veins / Q000166:cytology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D000889:Anti-Arrhythmia Agents; D051036:Large-Conductance Calcium-Activated Potassium Channels; D019831:Sodium-Calcium Exchanger; D013890:Thiourea; D002118:Calcium