title: Does the sarcoplasmic reticulum achieve chemiosmotic equilibrium in relaxed muscle?
abstract: Measurements of 45Ca2+ efflux from bovine skeletal muscle fibres preloaded with this isotope indicate that the sarcoplasmic free Ca2+ concentration rises and falls under anaerobic (or uncoupled) and aerobic conditions, respectively. Dantrolene has only a small effect on these responses which are larger in predominantly slow-twitch fibre preparations. Dantrolene slightly reduces the resting free Ca2+; this is much more pronounced in rectus abdominis (mainly fast-twitch) than in sternomandibularis (mainly slow-twitch). It is proposed that the sarcoplasmic reticulum in the resting muscle fibre achieves a state close to chemiosmotic equilibrium and that aerobic metabolism generates a higher phosphorylation potential, permitting a larger Ca2+ electrochemical potential difference to develop across the sarcoplasmic reticulum membrane under aerobic conditions.
mesh_terms: D019297:2,4-Dinitrophenol; D000693:Anaerobiosis; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D003486:Cyanides / Q000494:pharmacology; D003620:Dantrolene / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology; D009119:Muscle Contraction; D009126:Muscle Relaxation; D012519:Sarcoplasmic Reticulum / Q000502:physiology*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D003486:Cyanides; D004140:Dinitrophenols; D003620:Dantrolene; D019297:2,4-Dinitrophenol; D002118:Calcium