Cellular Biology |
From the Department of Medicine (Cardiology) and the Vascular Biology Group, University of Alberta, Canada.
Correspondence to Stephen L. Archer, MD, Heart and Stroke Chair in Cardiovascular Research, Cardiology Division, University of Alberta, WMC 2C2.36, 8440 112th St, Edmonton, Alberta T6G 2B7, Canada. E-mail sarcher{at}cha.ab.ca
Hypoxic pulmonary vasoconstriction (HPV) is initiated by inhibition of O2-sensitive, voltage-gated (Kv) channels in pulmonary arterial smooth muscle cells (PASMCs). Kv inhibition depolarizes membrane potential (EM), thereby activating Ca2+ influx via voltage-gated Ca2+ channels. HPV is weak in extrapulmonary, conduit pulmonary arteries (PA) and strong in precapillary resistance arteries. We hypothesized that regional heterogeneity in HPV reflects a longitudinal gradient in the function/expression of PASMC O2-sensitive Kv channels. In adult male Sprague Dawley rats, constrictions to hypoxia, the Kv blocker 4-aminopyridine (4-AP), and correolide, a Kv1.x channel inhibitor, were endothelium-independent and greater in resistance versus conduit PAs. Moreover, HPV was dependent on Kv-inhibition, being completely inhibited by pretreatment with 4-AP. Kv1.2, 1.5, Kv2.1, Kv3.1b, Kv4.3, and Kv9.3. mRNA increased as arterial caliber decreased; however, only Kv1.5 protein expression was greater in resistance PAs. Resistance PASMCs had greater K+ current (IK) and a more hyperpolarized EM and were uniquely O2 and correolide-sensitive. The O2-sensitive current (active at 65 mV) was resistant to iberiotoxin, with minimal tityustoxin sensitivity. In resistance PASMCs, 4-AP and hypoxia inhibited IK 57% and 49%, respectively, versus 34% for correolide. Intracellular administration of anti-Kv1.5 antibodies inhibited correolides effects. The hypoxia-sensitive, correolide-insensitive IK (15%) was conducted by Kv2.1. Anti-Kv1.5 and anti-Kv2.1 caused additive depolarization in resistance PASMCs (Kv1.5>Kv2.1) and inhibited hypoxic depolarization. Heterologously expressed human PASMC Kv1.5 generated an O2 and correolide-sensitive IK like that in resistance PASMCs. In conclusion, Kv1.5 and Kv2.1 account for virtually all the O2-sensitive current. HPV occurs in a Kv-enriched resistance zone because resistance PASMCs preferentially express O2-sensitive Kv-channels.
Key Words: immunoelectropharmacology laser capture microdissection voltage-gated channels pulmonary circulation adenoviral gene transfer
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