Formation and metabolism of inositol 1,3,4,5-tetrakisphosphate in liver.
The inositol lipid pools of isolated rat hepatocytes were labeled with [3H]myo-inositol, stimulated maximally with vasopressin and the relative contents of [3H]inositol phosphates were measured by high performance liquid chromatography. Inositol 1,4,5-trisphosphate accumulated rapidly (peak 20 s), while inositol 1,3,4-trisphosphate and a novel inositol phosphate (ascribed to inositol 1,3,4,5-tetrakisphosphate) accumulated at a slower rate over 2 min. Incubation of hepatocytes with 10 mM Li+ prior to vasopressin addition selectively augmented the levels of inositol monophosphate, inositol 1,4-bisphosphate, and inositol 1,3,4-trisphosphate. A kinase was partially purified from liver and brain cortex which catalyzed an ATP-dependent phosphorylation of [3H]inositol 1,4,5-trisphosphate to inositol 1,3,4,5-tetrakisphosphate. Incubation of purified [3H]inositol 1,3,4,5-tetrakisphosphate with diluted liver homogenate produced initially inositol 1,3,4-trisphosphate and subsequently inositol 1,3-bisphosphate, the formation of which could be inhibited by Li+. The data demonstrate that the most probable pathway for the formation of inositol 1,3,4,5-tetrakisphosphate is by 3-phosphorylation of inositol 1,4,5-trisphosphate by a soluble mammalian kinase. Degradation of both compounds occurs first by a Li+-insensitive 5-phosphatase and subsequently by a Li+-sensitive 4-phosphatase. The prolonged accumulation of both inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in vasopressin-stimulated hepatocytes suggest that they have separate second messenger roles, perhaps both relating to Ca2+-signalling events.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D008297:Male; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000494:pharmacology
D007295:Inositol Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; D014667:Vasopressins; D015544:Inositol 1,4,5-Trisphosphate; D008094:Lithium; D011494:Protein Kinases