title: Sodium ion and the neutrotransmitter-stimulated 32P labelling of phosphoinositides and other phospholipids in the iris muscle.
abstract: The effects of Na+, other cations and the neurotransmitters, acetylcholine and norepinephrine on 32Pi incorporation into phospholipids of the rabbit iris smooth muscle were investigated [1]. The basal 32P-labelling of phospholipids including phosphatidic acid, phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine and the polyphosphoinositides increased with Na+ concentration [2]. The neurotransmitter-stimulated 32P labelling of phosphatidic acid, phosphatidylinositol and phosphatidylcholine is dependent on the presence of extracellular Na+ [3]. The monovalent cation requirement for Na+ specific. Of the monovalent cations Li+, NH+4, K+, Choline+ and Tris, only Li+ partially substituted for Na+ [4]. A significant decrease in 32P labelling of phospholipids in response to acetylcholine was observed when Ca2+ and/or K+ were added to an isoosmotic medium deficient of Na+ [5]. Ouabain, which blocks the Na+-pump, inhibited the basal 32Pi incorporation into phosphatidylcholine and the acetylcholine-stimulated 32P labelling of phosphatidic acid, phosphatidylinositol and phosphatidylcholine [6]. It was suggested that phosphoinositide breakdown is associated with Ca2+ influx as we have previously reported (Akhtar, R.A. and Abdel-Latif, A.A. (1978) J. Pharmacol. Exp. Ther. 204, 655-668) and that the enhanced 32P-labelling of phosphoinositides could be associated with Na+ outflux, via the Na+-pump mechanism.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology; D005260:Female; D007498:Iris / Q000378:metabolism*; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology*
chemical_list: D002414:Cations, Monovalent; D018377:Neurotransmitter Agents; D010710:Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D010042:Ouabain; D012964:Sodium; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine