title: Does the inositol tris/tetrakisphosphate pathway exist in rat heart?
abstract: Appearance of two isomers of inositol trisphosphate (InsP3) was observed when [3H]inositol prelabelled rat heart ventricles were stimulated for 10 and 30 s with noradrenaline. In contrast, inositol tetrakisphosphate (InsP4) could not be detected. However the existence of the inositol tris/tetrakisphosphate pathway was demonstrated by studying [3H]inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) metabolism in a soluble fraction of rat heart. There, [3H]Ins-1,4,5-P3 was phosphorylated to form [3H]Ins-1,3,4,5-P4. Raising [Ca2+] from 1 nM to 1 microM increased InsP3 kinase activity by 2-fold (EC50 for Ca2+ approx. 56 nM). This effect appeared to be due to an increase of the apparent Vmax of the enzyme while the apparent Km was unchanged.
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006321:Heart / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000096:biosynthesis*; D007536:Isomerism; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010770:Phosphotransferases / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical; D013403:Sugar Phosphates / Q000096:biosynthesis*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; D001285:Atropine; D015544:Inositol 1,4,5-Trisphosphate; D011433:Propranolol; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D002118:Calcium; D009638:Norepinephrine