Functional interaction of ClCa with RyR and CaL in pulmonary arteries from chronic hypoxic sheep

Abstract

Agonists such as serotonin (5‐HT) mediate pulmonary artery (PA) contraction, in large part, through membrane depolarization, activation of L‐type Ca2+ channels (CaL) and subsequent cytosolic Ca2+ increases. The sequence leading from 5‐HT receptor stimulation through to contraction remains controversial. Experimental evidence suggests that calcium activated chloride channels (ClCa) are pivotal to the depolarization response and that ryanodine receptors (RyRs) are important to the activity of ClCa. These associations led us to test the hypothesis that ClCa‐mediated contractility is dependent on coordination with RyR as well as CaL. These hypotheses were tested by performing wire‐myography on isolated PA from adult chronic hypoxic sheep, where hypoxia was induced by housing sheep at 3,801 m for 100+ days. 5‐HT elicited dose‐dependent contractions were attenuated by inhibitors for ClCa (100 μM niflumic acid, NFA), CaL (10 μM nifedipine, NIF), and RyR (10 μM dantrolene, DAN) separately and combined. NIF alone or the combinations of NIF+NFA or NFA+DAN reduced 5‐HT elicited contractility to similar extents. NFA or DAN alone blocked contractility less effectively. These results support the proposal that 5‐HT receptor activation promotes PA contractility in chronic hypoxic sheep through the cooperative activity of RyR, ClCa and CaL. NIH P01HD031226, R01HD003807 (LDL), and R01 HL075477, NCRR P20 RR15581 (NL)