title: Rapid filtration studies of Ca2+-induced Ca2+ release from skeletal sarcoplasmic reticulum. Role of monovalent ions.
abstract: We have developed a rapid filtration technique for the measurement of Ca2+ release from isolated sarcoplasmic reticulum vesicles. Using this technique, we have studied the Ca2+-induced Ca2+ release of sarcoplasmic reticulum vesicles from rabbit skeletal muscle passively loaded with 5 mM Ca2+. The effect of known effectors (adenine nucleotides and caffeine) and inhibitors (Mg2+ and ruthenium red) of this release were investigated. In a medium composed of 100 mM KCl buffered at pH 6.8 with 20 mM K/3-(N-morpholino)propanesulfonic acid the Ca2+ release rate was maximal (500 nmol of Ca2+ released.(mg of protein)-1.s-1) at 1 micron external Ca2+ and 5 mM ATP. We also observed a rapid Ca2+ release induced by micromolar Ag+ in the presence of ATP (at 1 nM Ca2+). The Ag+-induced Ca2+ release was totally inhibited by 5 micron ruthenium red. We have also investigated the effect of monovalent ions on the Ca2+ release elicited by Ca2+ or Ag+. We show that the Ca2+ release rate: 1) was dependent upon the presence of K+ or Na+ in the release medium and 2) was influenced by a K+ gradient created across the sarcoplasmic reticulum membrane. These results directly support the idea of the involvement of an influx of K+ (through K+ channels) during the Ca2+ release and allow to reconsider a possible influence of the membrane potential of the sarcoplasmic reticulum on the Ca2+ release.
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism; D005374:Filtration; D007473:Ion Channels / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism* / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D000227:Adenine Nucleotides; D002712:Chlorides; D007473:Ion Channels; D012430:Ruthenium Red; D002110:Caffeine; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium