Calcium-induced calcium release from sarcoplasmic reticulum vesicles.
Passive permeability of sarcoplasmic reticulum vesicles for Ca2+ was studied by the Millipore filtration method using 45Ca. The efflux rate of Ca2+ increased in the presence of micromolar concentrations of Ca2+ in the medium when the Mg2+ concentration was low. The dependence of the Ca2+ release rate on the extravesicular Ca2+ concentration was not affected by the intravesicular Ca2+ concentration. The Ca2+ release was enhanced by caffeine, but reduced by procaine and Mg2+. These properties suggest that the Ca2+ release is a similar phenomenon to the Ca2+-induced Ca2+ release observed in skinned muscle fiber. Kinetic analysis of the efflux curves suggests that two types of vesicles exist in our preparation; about 2/3 of the vesicles release Ca2+ as described above and the remainder does not.
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D002110:Caffeine; D011343:Procaine; D008274:Magnesium; D002118:Calcium