title: Chemical modification of calcium release from the sarcoplasmic reticulum of mechanically skinned skeletal bullfrog muscle fibers.
abstract: Several types of reagents that react with amino acid side chains induced repetitive phasic contracture of skinned skeletal muscle from frogs. The presence of 10 mM procaine or 5 mM magnesium in the medium or disruption of the sarcoplasmic reticulum (SR) eliminated this contracture, indicating that the calcium-induced calcium-release mechanism of SR is involved in the contraction. Dithiothreitol inhibited the contracture induced by chloramine T, N-acetylimidazole, or p-chloromercuriphenylsulfonic acid (pCMPS) but not in the case of carbodiimide, phenylglyoxal, trinitrobenzenesulfonic acid, diethylpyrocarbonate (DEP), or N-chlorosuccinimide (NCS). Therefore, modification of groups other than the sulfhydryl ones seems to induce contractures under such conditions. The amplitude of the caffeine-induced contracture decreased after treatment with pCMPS, DEP, or NCS. NCS shifted the pCa-tension curve toward low pCa in the SR-disrupted fibers. This shift would explain the decrease in the caffeine contracture. It is tentatively concluded that pCMPS and DEP release a large amount of calcium from SR.
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000378:metabolism* / Q000648:ultrastructure; D011892:Rana catesbeiana; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D007202:Indicators and Reagents; D002110:Caffeine; D002118:Calcium