title: Adenine nucleotide stimulation of Ca2+-induced Ca2+ release in sarcoplasmic reticulum.
abstract: Rabbit skeletal muscle sarcoplasmic reticulum was fractionated into a "Ca2+-release" and "control" fraction by differential and sucrose gradient centrifugation. External Ca2+ (2-20 microM) caused the release of 40 nmol of 45Ca2+/mg of protein/s from Ca2+-release vesicles passively loaded at pH 6.8 with an internal half-saturation Ca2+ concentration of 10-20 mM. Ca2+-induced Ca2+ release had an approximate pK value of 6.6 and was half-maximally inhibited at an external Ca2+ concentration of 2 X 10(-4) M and Mg2+ concentration of 7 X 10(-5) M. 45Ca2+ efflux from control vesicles was slightly inhibited at external Ca2+ concentrations that stimulated the rapid release of Ca2+ from Ca2+-release vesicles. Adenine, adenosine, and derived nucleotides caused stimulation of Ca2+-induced Ca2+ release in media containing a "physiological" free Mg2+ concentration of 0.6 mM. At a concentration of 1 mM, the order of effectiveness was AMP-PCP greater than cAMP approximately AMP approximately ADP greater than adenine greater than adenosine. Other nucleoside triphosphates and caffeine were minimally effective in increasing 45Ca2+ efflux from passively loaded Ca2+-release vesicles. La3+, ruthenium red, and procaine inhibited Ca2+-induced Ca2+ release. Ca2+ flux studies with actively loaded vesicles also indicated that a subpopulation of sarcoplasmic reticulum vesicles contains a Ca2+ permeation system that is activated by adenine nucleotides.
mesh_terms: D000225:Adenine / Q000494:pharmacology; D000227:Adenine Nucleotides / Q000494:pharmacology*; D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D009132:Muscles / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D000227:Adenine Nucleotides; D000225:Adenine; D000241:Adenosine; D002118:Calcium