Résumé
Dahan D, Ducret T, Quignard J, Marthan R, Savineau J, Esteve E. Implication of the ryanodine receptor in TRPV4-induced calcium response in pulmonary arterial smooth muscle cells from normoxic and chronically hypoxic rats. Am J Physiol Lung Cell Mol Physiol 303: L824-L833, 2012. First published September 7, 2012; doi:10.1152/ajplung.00244.2011.-There is a growing body of evidence indicating that transient receptor potential (TRP) channels are implicated in calcium signaling and various cellular functions in the pulmonary vasculature. The aim of this study was to investigate the expression, functional role, and coupling to reticulum calcium channels of the type 4 vanilloid TRP subfamily (TRPV4) in the pulmonary artery from both normoxic (Nx) and chronically hypoxic (CH) rats. Activation of TRPV4 with the specific agonist 4 alpha-phorbol-12,13-didecanoate (4 alpha-PDD, 5 mu M) increased the intracellular calcium concentration ([Ca2+](i)). This effect was significantly reduced by a high concentration of ryanodine (100 mu M) or chronic caffeine (5 mM) that blocked ryanodine receptor (RyR) but was insensitive to xestospongin C (10 mu M), an inositol trisphosphate receptor antagonist. Inhibition of RyR1 and RyR3 only with 10 mu M of dantrolene did not attenuate the 4 alpha-PDD-induced [Ca2+](i) increase. Western blotting experiments revealed the expression of TRPV4 and RyR2 with an increase in both receptors in pulmonary arteries from CH rats vs. Nx rats. Accordingly, the 4 alpha-PDD-activated current, measured with patch-clamp technique, was increased in pulmonary artery smooth muscle cells (PASMC) from CH rats vs. Nx rats. 4 alpha-PDD increased isometric tension in artery rings, and this response was also potentiated under chronic hypoxia conditions. 4 alpha-PDD-induced calcium response, current, and contraction were all inhibited by the selective TRPV4 blocker HC-067047. Collectively, our findings provide evidence of the interplay between TRPV4 and RyR2 in the Ca2+ release mechanism and contraction in PASMC. This study provides new insights onto the complex calcium signaling in PASMC and point out the importance of the TRPV4-RyR2 signaling pathway under hypoxic conditions that may lead to pulmonary hypertension.