ALPHA-1-ADRENERGIC STIMULATION OF PHOSPHATIDYLINOSITOL-PHOSPHATIDIC ACID TURNOVER IN RAT PAROTID CELLS

  • 1 January 1982
    • journal article
    • research article
    • Vol. 21  (1) , 128-132
Abstract
The regulation of phosphatidylinositol turnover by .alpha.-adrenergic agonists in rat parotid acinar cell aggregates was examined with respect to kinetics and agonist-antagonist interactions. Phospatidylinositol turnover was followed by the changes in the specific activities of [32P]phosphatidic acid and [32P]phosphatidylinositol. The specific activity of phosphatidic acid increased rapidly (within 1 min) after addition of epinephrine (10-5 M), reached a maximal level within 12-16 min, and then decreased. Incorporation of 32P into phosphatidylinositol exhibited a lag phase of .apprx. 5 min and then increased continuously for an additional 40 min. The absolute amounts of phosphatidic acid and phosphatidylinositol did not change. The concentrations of epinephrine needed to stimulate 32P incorporation into phosphatidic acid and phosphatidylinositol, measured at 15 and 30 min, respectively, were similar; Ka values of 2.05 .+-. 0.46 .times. 10-6 M for phosphatidic acid and 2.98 .+-. 0.30 .times. 10-6 M for phosphatidylinositol were found. The effects of agonists on 32P labeling of phosphatidylinositol, in order of potency, were epinephrine .gtoreq. norepinephrine > phenylephrine .mchgt. normetanephrine. When various adrenergic antagonists were evaluated for their ability to inhibit 10-5 M epinephrine-stimulated 32P incorporation into both phosphatidic acid and phosphatidylinositol, the order of antagonist potency was prazosin .gtoreq. phenoxybenzamine > phentolamine .gtoreq. yohimbine .mchgt. propranolol. Evidently, phosphatidylinositol-phosphatidic acid turnover in the rat parotid gland is mediated by the .alpha.1-adrenergic receptor system.