Inhibition of endothelium-dependent vasorelaxation by extracellular K+: a novel controlling signal for vascular contractility

Open Access
Publisher Website
Google Scholar
Abstract
The effects of extracellular K+on endothelium-dependent relaxation (EDR) and on intracellular Ca2+concentration ([Ca2+]i) were examined in mouse aorta, mouse aorta endothelial cells (MAEC), and human umbilical vein endothelial cells (HUVEC). In mouse aortic rings precontracted with prostaglandin F2αor norepinephrine, an increase in extracellular K+concentration ([K+]o) from 6 to 12 mM inhibited EDR concentration dependently. In endothelial cells, an increase in [K+]oinhibited the agonist-induced [Ca2+]iincrease concentration dependently. Similar to K+, Cs+also inhibited EDR and the increase in [Ca2+]iconcentration dependently. In current-clamped HUVEC, increasing [K+]ofrom 6 to 12 mM depolarized membrane potential from –32.8 ± 2.7 to –8.6 ± 4.9 mV ( n = 8). In voltage-clamped HUVEC, depolarizing the holding potential from –50 to –25 mV decreased [Ca2+]isignificantly from 0.95 ± 0.03 to 0.88 ± 0.03 μM ( n = 11, P < 0.01) and further decreased [Ca2+]ito 0.47 ± 0.04 μM by depolarizing the holding potential from –25 to 0 mV ( n = 11, P < 0.001). Tetraethylammonium (1 mM) inhibited EDR and the ATP-induced [Ca2+]iincrease in voltage-clamped MAEC. The intermediate-conductance Ca2+-activated K+channel openers 1-ethyl-2-benzimidazolinone, chlorozoxazone, and zoxazolamine reversed the K+-induced inhibition of EDR and increase in [Ca2+]i. The K+-induced inhibition of EDR and increase in [Ca2+]iwas abolished by the Na+-K+pump inhibitor ouabain (10 μM). These results indicate that an increase of [K+]oin the physiological range (6–12 mM) inhibits [Ca2+]iincrease in endothelial cells and diminishes EDR by depolarizing the membrane potential, decreasing K+efflux, and activating the Na+-K+pump, thereby modulating the release of endothelium-derived vasoactive factors from endothelial cells and vasomotor tone.