title: Inositol 1,4,5-trisphosphate-induced calcium release from canine aortic sarcoplasmic reticulum vesicles.
abstract: Inositol 1,4,5-trisphosphate-induced calcium release from canine aortic smooth muscle sarcoplasmic reticulum vesicles was examined using the calcium indicator antipyrylazo III. Calcium release was initiated by addition of inositol 1,4,5-trisphosphate (IP3) to aortic vesicles 7 min after initiation of ATP-supported calcium uptake. Half-maximal calcium release occurred at 1 microM IP3, with maximal calcium release amounting to 25 +/- 2% of the intravesicular calcium (n = 12, 9 preparations). Ruthenium red (10-20 microM), which has been reported to block IP3-induced calcium release from skeletal muscle sarcoplasmic reticulum, did not inhibit aortic IP3-induced calcium release. Elevation of Mg2+ concentration from 0.06 to 7.8 mM inhibited aortic IP3-induced calcium release 75%, which contrasts with the Mg2+-insensitive IP3-induced calcium release from platelet reticular membranes. The IP3-dependence of aortic calcium release suggested that Mg2+ acted as a noncompetitive inhibitor. Thus, aortic sarcoplasmic reticulum vesicles contain an IP3-sensitive calcium pathway which is inhibited by millimolar concentrations of Mg2+, but which is not inhibited by Ruthenium red and so differs from the previously described IP3-sensitive calcium pathways in skeletal muscle and platelet reticular membranes.
mesh_terms: D000818:Animals; D001011:Aorta; D001693:Biological Transport, Active / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D006321:Heart / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D012430:Ruthenium Red / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013403:Sugar Phosphates / Q000494:pharmacology*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D012430:Ruthenium Red; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D008274:Magnesium; D002118:Calcium