Mitochondria regulate TRPV4-mediated release of ATP

TLDR: Depolarised mitochondria switch TRPV4 signalling from relying on Ca-induced Ca release at IP receptors, to being independent of Ca influx and instead mediated by ATP release via pannexins, highlighting a previously unknown role of mitochondria in shaping TRpV4 mediated Ca signalling by facilitating ATP release.

Abstract: Background and Purpose: Ca2+ influx via TRPV4 channels triggers Ca2+ release from the IP3‐sensitive internal store to generate repetitive oscillations. Although mitochondria are acknowledged regulators of IP3‐mediated Ca2+ release, how TRPV4‐mediated Ca2+ signals are regulated by mitochondria is unknown. We show that depolarised mitochondria switch TRPV4 signalling from relying on Ca2+‐induced Ca2+ release at IP3 receptors to being independent of Ca2+ influx and instead mediated by ATP release via pannexins. Experimental Approach: TRPV4‐evoked Ca2+ 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 Ca2+ oscillations that required Ca2+ influx. However, when the mitochondrial membrane potential was depolarised, by the uncoupler CCCP or complex I inhibitor rotenone, TRPV4 activation generated large propagating, multicellular, Ca2+ waves in the absence of external Ca2+. The ATP synthase inhibitor oligomycin did not potentiate TRPV4‐mediated Ca2+ signals. GSK‐evoked Ca2+ 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 Ca2+ 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 Ca2+ signalling by facilitating ATP release. When mitochondria are depolarised, TRPV4‐mediated release of ATP via pannexin channels activates plasma membrane purinergic receptors to trigger IP3‐evoked Ca2+ release.