K(+) channel inhibition, calcium signaling, and vasomotor tone in canine pulmonary artery smooth muscle.
We investigated the role of K(+) channels in the regulation of baseline intracellular free Ca(2+) concentration ([Ca(2+)](i)), alpha-adrenoreceptor-mediated Ca(2+) signaling, and capacitative Ca(2+) 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 [Ca(2+)](i) but attenuated the amplitude and frequency of the [Ca(2+)](i) oscillations induced by the alpha-agonist phenylephrine (PE). Inhibition of Ca(2+)-activated K(+) channels (with charybdotoxin) and inhibition (with glibenclamide) or activation of ATP-sensitive K(+) channels (with lemakalim) had no effect on resting [Ca(2+)](i) or PE-induced [Ca(2+)](i) oscillations. Thapsigargin was used to deplete sarcoplasmic reticulum Ca(2+) stores in the absence of extracellular Ca(2+). Under these conditions, 4-AP attenuated the peak and sustained components of capacitative Ca(2+) entry, which was observed when extracellular Ca(2+) was restored. Capacitative Ca(2+) 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 [Ca(2+)](i) and tone in PASMCs but attenuates the response to PE, likely via inhibition of capacitative Ca(2+) entry.
Center for Anesthesiology Research, Division of Anesthesiology and Critical Care Medicine, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
S
S
Doi
D S
DS
Damron
K
K
Ogawa
S
S
Tanaka
M
M
Horibe
P A
PA
Murray
D015761:4-Aminopyridine / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D019806:Cromakalim / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000819:agonists; D011651:Pulmonary Artery / Q000166:cytology / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology; D014666:Vasomotor System / Q000166:cytology / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014665:Vasodilator Agents; D019806:Cromakalim; D010656:Phenylephrine; D019284:Thapsigargin; D015761:4-Aminopyridine; D005905:Glyburide