Mitochondria regulate TRPV4‐mediated release of ATP

Background and Purpose Ca 2+ influx via TRPV4 channels triggers Ca 2+ release from the IP 3 ‐sensitive internal store to generate repetitive oscillations. Although mitochondria are acknowledged regulators of IP 3 ‐mediated Ca 2+ release, how TRPV4‐mediated Ca 2+ signals are regulated by mitochondria is unknown. We show that depolarised mitochondria switch TRPV4 signalling from relying on Ca 2+ ‐induced Ca 2+ release at IP 3 receptors to being independent of Ca 2+ influx and instead mediated by ATP release via pannexins. Experimental Approach TRPV4‐evoked Ca 2+ signals were individually examined in hundreds of cells in the endothelium of rat mesenteric resistance arteries using the indicator Cal520. Key Results TRPV4 activation with GSK1016790A (GSK) generated repetitive Ca 2+ oscillations that required Ca 2+ influx. However, when the mitochondrial membrane potential was depolarised, by the uncoupler CCCP or complex I inhibitor rotenone, TRPV4 activation generated large propagating, multicellular, Ca 2+ waves in the absence of external Ca 2+ . The ATP synthase inhibitor oligomycin did not potentiate TRPV4‐mediated Ca 2+ signals. GSK‐evoked Ca 2+ waves, when mitochondria were depolarised, were blocked by the TRPV4 channel blocker HC067047, the SERCA inhibitor cyclopiazonic acid, the PLC blocker U73122 and the inositol trisphosphate receptor blocker caffeine. The Ca 2+ waves were also inhibited by the extracellular ATP blockers suramin and apyrase and the pannexin blocker probenecid. Conclusion and Implications These results highlight a previously unknown role of mitochondria in shaping TRPV4‐mediated Ca 2+ signalling by facilitating ATP release. When mitochondria are depolarised, TRPV4‐mediated release of ATP via pannexin channels activates plasma membrane purinergic receptors to trigger IP 3 ‐evoked Ca 2+ release.