title: Isolation of terminal cisternae of frog skeletal muscle. Calcium storage and release properties.
abstract: Sarcoplasmic reticulum (SR) terminal cisternae (TC) of frog (Rana esculenta) fast-twitch skeletal muscle have been purified by isopycnic sucrose density gradient centrifugation. Biochemical characteristics and Ca2+ release properties have been investigated and compared to those of the homologous fraction of rabbit skeletal muscle TC. The frog SR fraction obtained at the 38/45% sucrose interface appears to be derived from the terminal cisternae region as judged by: (a) thin section electron microscopy showing vesicles containing electron opaque material and squarelike (feet) projections at the outer surface; (b) protein composition (Ca2+-ATPase, calsequestrin, and high Mr proteins); (c) Ca2+ fluxes properties. The content of calsequestrin was higher in frog TC by 50% and the Ca2+ binding capacity (624 or 45 nmol of Ca2+/mg of TC protein, depending upon experimental conditions) was 3-4 times that of rabbit TC. Species-specific antigenic differences were found between junctional SR proteins of frog and rabbit TC. After active Ca2+ preloading in the presence of pyrophosphate (Palade, P. (1987) J. Biol. Chem. 262, 6135-6141), caffeine and doxorubicin elicited Ca2+ release from either TC fraction but with much faster rates in frog TC than in rabbit TC (14 versus 3 mumol of Ca2+/min/mg of protein). The present results provide new evidence for the existence of marked differences in Ca2+ release properties between TC of amphibian and mammalian fast-twitch muscle. Higher Ca2+ binding capacity and faster release rates in frog TC might compensate for the comparably greater diffusion distance being covered by the released Ca2+ from the Z-line to the actomyosin cross-bridges in the A-I overlap region.
authors.affiliation: Centro di Studio per la Biologia e la Fisiopatologia Muscolare del Consiglio Nazionale delle Ricerche, Università di Padova, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Volpe
authors.forename: M
authors.initials: M
authors.lastname: Bravin
authors.forename: F
authors.initials: F
authors.lastname: Zorzato
authors.forename: A
authors.initials: A
authors.lastname: Margreth
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002155:Calsequestrin / Q000032:analysis / Q000378:metabolism; D002458:Cell Fractionation; D002500:Centrifugation, Isopycnic; D004317:Doxorubicin / Q000494:pharmacology; D008055:Lipids / Q000032:analysis; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000032:analysis; D009132:Muscles / Q000648:ultrastructure*; D011817:Rabbits; D011893:Rana esculenta; D012519:Sarcoplasmic Reticulum / Q000032:analysis / Q000378:metabolism* / Q000648:ultrastructure; D013045:Species Specificity
chemical_list: D002155:Calsequestrin; D008055:Lipids; D009124:Muscle Proteins; D000001:Calcimycin; D002110:Caffeine; D004317:Doxorubicin; D000252:Calcium-Transporting ATPases; D002118:Calcium