Phosphatidylinositol metabolism in rat hepatocytes stimulated by vasopressin.
In isolated rat hepatocytes, vasopressin evoked a large increase in the incorporation of [32P]Pi into phosphatidylinositol, accompanied by smaller increases in the incorporation of [1-14C]oleate and [U-14C]glycerol. Incorporation of these precursors into the other major phospholipids was unchanged during vasopressin treatment. Vasopressin also promoted phosphatidylinositol breakdown in hepatocytes. Half-maximum effects on phosphatidylinositol breakdown and on phosphatidylinositol labelling occurred at about 5 nM-vasopressin, a concentration at which approximately half of the hepatic vasopressin receptors are occupied but which is much greater than is needed to produce half-maximal activation of glycogen phosphorylase. Insulin did not change the incorporation of [32P]Pi into the phospholipids of hepatocytes and it had no effect on the response to vasopressin. Although the incorporation of [32P]Pi into hepatocyte lipids was decreased when cells were incubated in a Ca2+-free medium, vasopressin still provoked a substantial stimulation of phosphatidylinositol labelling under these conditions. Studies with the antagonist [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid),8-arginine]vasopressin indicated that the hepatic vasopressin receptors that control phosphatidylinositol metabolism are similar to those that mediate the vasopressor response in vivo. When prelabelled hepatocytes were stimulated for 5 min and then subjected to subcellular fractionation. The decrease in [3H]phosphatidylinositol content in each cell fraction with approximately in proportion to its original phosphatidylinositol content. This may be a consequence of phosphatidylinositol breakdown at a single site, followed by rapid phosphatidylinositol exchange between membranes leading to re-establishment of an equilibrium distribution.
D000818:Animals; D001127:Arginine Vasopressin / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D013268:Stimulation, Chemical; D014667:Vasopressins / Q000494:pharmacology*
D007328:Insulin; D010716:Phosphatidylinositols; D010743:Phospholipids; D014667:Vasopressins; D001127:Arginine Vasopressin; C025044:argipressin, beta-mercapto-beta,beta cyclopentamethylenepropionic acid(1)-; D002118:Calcium