Mitochondria regulate TRPV4-mediated release of ATP

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.

Keywords: TRPV4; endothelium; inositol 1,4,5-trisphosphate (IP3); intercellular Ca2+ waves; intercellular communication; mitochondria; pannexin; purinergic receptors; vascular.