title: Inositol 1,4,5-trisphosphate but not ryanodine-receptor agonists induces calcium release from rat liver Golgi apparatus membrane vesicles.
abstract: We investigated the direct effect of inositol 1,4,5-trisphosphate (IP(3)) and ryanodine receptor agonists on Ca(2+) release from vesicles of a rat liver Golgi apparatus (GA) enriched fraction, which were actively loaded with (45)Ca(2+). Results in GA were compared with those obtained in a rat liver endoplasmic reticulum (ER) enriched fraction. The addition of IP(3) at concentrations ranging from 100 nm to 100 microm, in the presence of thapsigargin, a specific inhibitor of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases, promoted a rapid decrease in the Ca(2+) content of GA vesicles. The amount of Ca(2+) released from the vesicles was a function of IP(3) concentration, reaching about 60% in both GA and ER fractions at 100 microm IP(3). Calcium release was inhibited by heparin, an antagonist of IP(3) receptors. Calcium exhibited a bell-shaped effect on IP(3)-dependent Ca(2+) released from GA vesicles: it activated Ca(2+) release at concentrations up to 1 microm, and inhibited it at higher concentrations. In contrast to that found in the endoplasmic reticulum fraction, none of the ryanodine receptor agonists tested (cyclic ADP-ribose, caffeine and ryanodine) significantly induced Ca(2+) release from GA fraction vesicles in the presence of thapsigargin. Our results indicate the presence of an IP(3)-sensitive Ca(2+) release mechanism in the Golgi apparatus membrane analogous to that of the ER. However, a Ca(2+) release mechanism sensitive to ryanodine receptor agonists like that of ER is not evident in the GA membrane.
authors.affiliation: Laboratorio de Fisiología Celular, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile.
authors.forename: A
authors.initials: A
authors.lastname: Surroca
authors.forename: D
authors.initials: D
authors.lastname: Wolff
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D036563:Cyclic ADP-Ribose; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D036563:Cyclic ADP-Ribose; D012433:Ryanodine; D000246:Adenosine Diphosphate Ribose; D002110:Caffeine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases