Effects of acetylcholine and norepinephrine on incorporation of [ 32P]orthophosphate into phospholipids of rabbit iridial processes and iris smooth muscle

We have investigated: ( a) phospholipid composition, inclusive of higher inositides, of rabbit iridial processes and iris smooth muscles; ( b) 32P i incorporation into their respective phospholipids, and ( c) the effects of muscarinic cholinergic and adrenergic agonists and antagonists on 32P labelling of phospholipids of the iridial processes and iris smooth muscle. (1) Phosphatidylcholine, phosphatidylethanolamine, their respective plasmalogens and sphingomyelin, were found to be the major phospholipids in the iridial processes and iris smooth muscle. They constituted about 85% of the total phospholipids of these ocular tissues. (2) Both iridial processes and iris smooth muscles rapidly incorporated 32P i and [1- 14C]-arachidonic acid into their respective phospholipids, however this incorporation amounted to only 20% of that found for the whole iris-ciliary body. This could suggest a metabolic interrelationship between the iridial processes and the smooth muscle of the iris. (3) Addition of acetylcholine and norepinephrine to the iridial processes and iris smooth muscle increased 32P labelling of phosphatidic acid and phosphatidylinositol of the tissues. The increase in phospholipid labelling was higher in the iridial processes as compared to the iris smooth muscle. The effect of acetylcholine was blocked by atropine and that of norepinephrine was blocked by phentolamine and prazosin but not by yohimbine. This suggests that the observed effects of these neurotransmitters on phospholipid phosphorylation in the iridial processes and iris smooth muscle are mediated through muscarinic cholinergic and α 1-adrenergic receptors, respectively. The data presented provide additional support for the concept that in the iris-ciliary body the neurotransmitter-induced 32P labelling of phosphoinositides is probably linked to the functional activities of this tissue.