Canonical Transient Receptor Potential 4 Protein Encodes High Frequency Calcium Transients in Severe Pulmonary Arterial Hypertension

Canonical transient receptor potential 4 protein (TRPC4) comprises an endothelial store‐operated calcium entry channel, and TRPC4 inactivation confers a survival benefit in pulmonary arterial hypertension (PAH). Store‐operated endothelial Ca 2+ signals mediated by TRPC4 enhance vascular permeability, but the contribution of TRPC4 to endothelial cytosolic Ca 2+ signals and to the regulation of endothelial permeability in the vasculopathy of PAH is poorly understood. Therefore, we tested the hypothesis that TRPC4 increases the frequency of localized endothelial Ca 2+ transients and vascular permeability in PAH. We measured permeability in isolated perfused lungs, and found that TRPC4 exaggerated permeability responses to thapsigargin in Sugen/hypoxia treated hypertensive rats. We compared the endothelial Ca 2+ activity of wild type and TRPC4 knockout hypertensive rats using confocal microscopy, and evaluated how Ca 2+ signals were influenced in response to thapsigargin and sequential treatment with acetylcholine. We found that thapsigargin‐stimulated Ca 2+ signals were increased in hypertension, and recovered by TRPC4 inactivation. Store depletion revealed bimodal Ca 2+ responses to acetylcholine, with both short (<30 s) and long duration (>30 s) populations. Robust long duration responses to acetylcholine were abolished in PAH. Thus, TRPC4 underlies an exaggerated endothelial permeability response in hypertension. Furthermore, TRPC4 increased the frequency of endothelial Ca 2+ transients in severe pulmonary arterial hypertension, suggesting that TRPC4 provides a calcium source associated with endothelial dysfunction in the pathophysiology of PAH. Support or Funding Information This work was funded by NIH grants HL60024 and HL66299