Abstract
Background and Purpose Ca2+ influx via TRPV4
triggers Ca2+ release from the
IP3-sensitive internal store to generate repetitive
oscillations. While 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 ResultsTRPV4
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 phospholipase C (PLC) blocker U73122 and the
inositol triphosphate receptor (IP3 R) 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.