title: Reduced Ca(2+)-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum at low pH.
abstract: The purpose of this investigation was to determine the effects of reduced pH on Ca(2+)-induced Ca2+ release (CICR) from skeletal muscle sarcoplasmic reticulum (SR). Frog semitendinosus fiber bundles (1-3/bundle) were chemically skinned via saponin treatment (50 micrograms/mL, 20 min), which removes the sarcolemma and leaves the SR functional. The SR was first depleted of Ca2+ then loaded for 2 min at pCa (log free Ca2+ concentration) 6.6. CICR was then evoked by exposing the fibers to pCa 5-7 for 5-60 s. CICR was evoked both in the absence of ATP and Mg2+ and in the presence of beta, gamma-methyleneadenosine-5'-triphosphate (AMPPCP, a nonhydrolyzable form of ATP) and Mg2+. Ca2+ remaining in the SR was then assayed via caffeine (25 mM) contracture. In all cases, CICR evoked at pH 6.5 resulted in larger caffeine contractures than that evoked at 7.0, suggesting that more Ca2+ was released during CICR at the higher pH. Accordingly, rate constants for CICR were significantly greater at pH 7.0 than at pH 6.5. These results indicate that reduced pH depresses CICR from skeletal muscle SR.
authors.affiliation: Muscular Function Laboratory, Virginia Polytechnic Institute and State University, Blacksburg 24061-0326.
authors.forename: J H
authors.initials: JH
authors.lastname: Williams
authors.forename: C W
authors.initials: CW
authors.lastname: Ward
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D011894:Rana pipiens; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002110:Caffeine; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium