title: Ca2+-activated K+ channels in murine endothelial cells: block by intracellular calcium and magnesium.
abstract: The intermediate (IK(Ca)) and small (SK(Ca)) conductance Ca(2+)-sensitive K(+) channels in endothelial cells (ECs) modulate vascular diameter through regulation of EC membrane potential. However, contribution of IK(Ca) and SK(Ca) channels to membrane current and potential in native endothelial cells remains unclear. In freshly isolated endothelial cells from mouse aorta dialyzed with 3 microM free [Ca(2+)](i) and 1 mM free [Mg(2+)](i), membrane currents reversed at the potassium equilibrium potential and exhibited an inward rectification at positive membrane potentials. Blockers of large-conductance, Ca(2+)-sensitive potassium (BK(Ca)) and strong inward rectifier potassium (K(ir)) channels did not affect the membrane current. However, blockers of IK(Ca) channels, charybdotoxin (ChTX), and of SK(Ca) channels, apamin (Ap), significantly reduced the whole-cell current. Although IK(Ca) and SK(Ca) channels are intrinsically voltage independent, ChTX- and Ap-sensitive currents decreased steeply with membrane potential depolarization. Removal of intracellular Mg(2+) significantly increased these currents. Moreover, concomitant reduction of the [Ca(2+)](i) to 1 microM caused an additional increase in ChTX- and Ap-sensitive currents so that the currents exhibited theoretical outward rectification. Block of IK(Ca) and SK(Ca) channels caused a significant endothelial membrane potential depolarization (approximately 11 mV) and decrease in [Ca(2+)](i) in mesenteric arteries in the absence of an agonist. These results indicate that [Ca(2+)](i) can both activate and block IK(Ca) and SK(Ca) channels in endothelial cells, and that these channels regulate the resting membrane potential and intracellular calcium in native endothelium.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Vermont, Burlington 05405, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Ledoux
authors.forename: Adrian D
authors.initials: AD
authors.lastname: Bonev
authors.forename: Mark T
authors.initials: MT
authors.lastname: Nelson
mesh_terms: D000465:Algorithms; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002478:Cells, Cultured; D018999:Charybdotoxin / Q000494:pharmacology; D004594:Electrophysiology; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D014966:Xanthenes / Q000378:metabolism
chemical_list: D000814:Aniline Compounds; C409648:Fluo 4; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496900:Kcnn3 protein, mouse; C496925:Kcnn4 protein, mouse; D024681:Potassium Channels, Calcium-Activated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D014966:Xanthenes; D018999:Charybdotoxin; D001030:Apamin; D011189:Potassium Chloride; D008274:Magnesium; D002118:Calcium