title: Effects of compound 48/80 on the Ca2+ release by reversal of the Ca2+ pump and by the Ca2+ channel of sarcoplasmic reticulum membranes.
abstract: The effect of the calmodulin antagonist, compound 48/80, on the Ca2+ release from skeletal muscle sarcoplasmic reticulum was investigated. Both the Ca2+ release by reversal of the Ca2+ pump and the Ca2+ release by the Mg2(+)-controlled Ca2+ channel were studied. It was observed that, when reversal of the pump is inoperative and Mg2+ is not present in the reaction medium, 48/80 stimulates Ca2+ release from the vesicles. In contrast, in the presence of Mg2+, which blocks the Ca2+ channel, 48/80 inhibits Ca2+ release induced by ADP and Pi. This effect is strong at low concentrations of Pi (approximately 1 mM), whereas high concentrations (approximately 15 mM) protect the system against the drug. Furthermore, it was observed that 48/80 has a maximum effect on the channel-mediated Ca2+ release at concentrations of about 20 micrograms/ml, whereas maximal inhibition of the pump-mediated Ca2+ release occurs at concentrations of about 60-80 micrograms/ml. The results indicate that both the Ca2+ channel complex and the Ca2(+)-ATPase may be target systems for the effects of 48/80 on the Ca2+ transport activity of sarcoplasmic reticulum. However, the Ca2+ channel is more sensitive to the drug, suggesting an involvement of calmodulin on this mechanism of Ca2+ release.
authors.affiliation: Department of Zoology, University of Coimbra, Portugal.
authors.forename: M G
authors.initials: MG
authors.lastname: Vale
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D010710:Phosphates / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
chemical_list: D015220:Calcium Channels; D010710:Phosphates; D003189:p-Methoxy-N-methylphenethylamine; D000244:Adenosine Diphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium