Vascular smooth muscle cells are submitted to stretch forces exerted by the blood pressure. Pulmonary arteries can transduce a mechanical stimulus of stretch into a biological response of contraction, a mechanism called myogenic tone, which involves plasma membrane Ca²⁺ stretch-activated channels (SAC). As membrane plasticity and shape are important for the SAC activity, we investigate the involvement of caveolae in the Ca²⁺ and contraction response to stretch of pulmonary arterial smooth muscle cells (PA-SMC).

Isometric contractions were performed in pulmonary arterial vessels from normoxic rats (Nx rats) and rats with a pulmonary hypertension induced by a chronic hypoxia of 3weeks (CH rats). Inward currents from SAC were recorded on freshly isolated PA-SMC after a negative pressure applied by a patch-clamp pipette and Ca²⁺ variations were simultaneously recorded with the fluorescent probe indo-1. Sarcoplasmic reticulum Ca²⁺ was measured by a confocal microscope with the fluo-5N probe. Finally, a pharmacological approach using methyl-β-cyclodextrin (MβCD, a caveolae disrupter) coupled with different immunolabelings of caveolin-1 and sarcoplasmic Ca²⁺ stores were used to investigate the role of caveolae.

We show that caveolae are present and caveolin-1 expressed in PA-SMC from both normal and pulmonary hypertensive rats. Isolated PA-SMC and pulmonary arteries exhibit a higher SAC activity, Ca²⁺ response and contraction to stretch in CH rats than in Nx rats. These responses are reduced by MβCD only in CH rats. In the absence of extracellular calcium, a stretch induces a Ca²⁺ and contraction response only in CH rats but not in Nx rats. This phenomenon involves a Ca²⁺ release from the sarcoplasmic reticulum and is fully inhibited by MβCD.

Caveolae are important for stretch-induced calcium response in CH rats via a new subcellular organization between caveolae and intracellular calcium stores.