EXCITATION‐METABOLISM COUPLING: ROLE OF MEMBRANE DEPOLARIZATION ON THE MITOCHONDRIAL FUNCTION

Abstract

IntroductionDepolarizing stimuli induce signaling pathways in muscle that have pleiotropic effects. Two new voltage‐dependent phenomena, excitation‐transcription and excitation‐metabolism coupling (EMC), add to the canonical excitation‐contraction coupling process. The mechanisms involved in EMC, however, remain poorly understood.Material and MethodsMice were used at 6–8 weeks. Changes in mitochondrial and cytoplasmic Ca2+ levels were evaluated in living fibers from Flexor digitorum brevis muscle via imaging of fibers transfected with suitable plasmids. The mitochondrial potential and oxygen consumption were evaluated with Seahorse system and TMRE+ respectively.ResultsDepolarization of skeletal muscle fibers increased the cytoplasmic and mitochondrial Ca2+ levels, as detected using R‐CaM and CEPIA‐mt3, respectively. The depolarization‐dependent mitochondrial Ca2+ increase was partly prevented by dantrolene (50 μM), xestospongin B (10 μM) or IP3R1 knockdown, and was completely suppressed when using both inhibitors. Fibers pre‐incubated with apyrase (2 U/mL) displayed partially inhibited stimulation‐induced mitochondrial Ca2+ increase. Muscle cells were pre‐incubated with caged‐IP3 (5 μM); photo‐release of IP3 induced a transient increase in mitochondria Ca2+ levels that was inhibited by xestospongin B infibers. Finally, depolarization incrased mitocrondrial membrane potencial and oxygen consumption and these effects were partially reduced by IP3R knockdown.DiscussionAll these results suggest that activation of IP3R1 and RyR1 mediated Ca2+ release contribute to the mitochondrial Ca2+ increase and mitochondrial function produced by muscle activation.Support or Funding InformationFONDECYT (11130267, 1151293), PIA‐ACT1111, CONICYT 21150604