Increased TMEM16A-encoded calcium-activated chloride channel activity is associated with pulmonary hypertension

Forrest AS, Joyce TC, Huebner ML, Ayon RJ, Wiwchar M, Joyce J, Freitas N, Davis AJ, Ye L, Duan DD, Singer CA, Valencik ML, Greenwood IA, Leblanc N. Increased TMEM16A-encoded calcium-activated chloride channel activity is associated with pulmonary hypertension. Am J Physiol Cell Physiol 303: C1229-C1243, 2012. First published August 29, 2012; doi: 10.1152/ajpcell.00044.2012.-Pulmonary artery smooth muscle cells (PASMCs) are more depolarized and display higher Ca2+ levels in pulmonary hypertension (PH). Whether the functional properties and expression of Ca2+-activated Cl- channels (Cl-Ca), an important excitatory mechanism in PASMCs, are altered in PH is unknown. The potential role of Cl-Ca channels in PH was investigated using the monocrotaline (MCT)-induced PH model in the rat. Three weeks postinjection with a single dose of MCT (50 mg/kg ip), the animals developed right ventricular hypertrophy (heart weight measurements) and changes in pulmonary arterial flow (pulse-waved Doppler imaging) that were consistent with increased pulmonary arterial pressure and PH. Whole cell patch experiments revealed an increase in niflumic acid (NFA)-sensitive Ca2+-activated Cl- current [I-Cl(Ca)] density in PASMCs from large conduit and small intralobar pulmonary arteries of MCT-treated rats vs. aged-matched saline-injected controls. Quantitative RT-PCR and Western blot analysis revealed that the alterations in I-Cl(Ca) were accompanied by parallel changes in the expression of TMEM16A, a gene recently shown to encode for Cl-Ca channels. The contraction to serotonin of conduit and intralobar pulmonary arteries from MCT-treated rats exhibited greater sensitivity to nifedipine (1 mu M), an L-type Ca2+ channel blocker, and NFA (30 or 100 mu M, with or without 10 mu M indomethacin to inhibit cyclooxygenases) or T16A(Inh)-A01 (10 mu M), TMEM16A/Cl-Ca channel inhibitors, than that of control animals. In conclusion, augmented Cl-Ca/TMEM16A channel activity is a major contributor to the changes in electromechanical coupling of PA in this model of PH. TMEM16A-encoded channels may therefore represent a novel therapeutic target in this disease.