K+ channel inhibition, calcium signaling, and vasomotor tone in canine pulmonary artery smooth muscle

Abstract

We investigated the role of K+ channels in the regulation of baseline intracellular free Ca2+ concentration ([Ca2+]i), α-adrenoreceptor-mediated Ca2+ signaling, and capacitative Ca2+ entry in pulmonary artery smooth muscle cells (PASMCs). Inhibition of voltage-gated K+ channels with 4-aminopyridine (4-AP) increased the membrane potential and the resting [Ca2+]i but attenuated the amplitude and frequency of the [Ca2+]i oscillations induced by the α-agonist phenylephrine (PE). Inhibition of Ca2+-activated K+ channels (with charybdotoxin) and inhibition (with glibenclamide) or activation of ATP-sensitive K+ channels (with lemakalim) had no effect on resting [Ca2+]i or PE-induced [Ca2+]i oscillations. Thapsigargin was used to deplete sarcoplasmic reticulum Ca2+ stores in the absence of extracellular Ca2+. Under these conditions, 4-AP attenuated the peak and sustained components of capacitative Ca2+ entry, which was observed when extracellular Ca2+ was restored. Capacitative Ca2+ entry was unaffected by charybdotoxin, glibenclamide, or lemakalim. In isolated pulmonary arterial rings, 4-AP increased resting tension and caused a leftward shift in the KCl dose-response curve. In contrast, 4-AP decreased PE-induced contraction, causing a rightward shift in the PE dose-response curve. These results indicate that voltage-gated K+ channel inhibition increases resting [Ca2+]i and tone in PASMCs but attenuates the response to PE, likely via inhibition of capacitative Ca2+entry.