Acetylcholine increases the breakdown of triphosphoinositide of rabbit iris muscle prelabelled with [32P] phosphate

Abstract

1. Paired iris smooth muscles from rabbits were incubated for 30min at 37°C in an iso-osmotic salt medium containing glucose, inositol, cytidine and [32P]phosphate. 2. One of the pair was then incubated at 37'C for 10min in unlabelled medium containing lOmM-2-deoxyglucose and the other was incubated in the presence of acetylcholine plus eserine (0.05mM each). 2-Deoxyglucose, which was included in the incubation medium to minimize the biosynthesis of triphosphoinositide from ATP and diphosphoinositide, decreased the amount of labelled ATP by 71 % and inhibited further 32p incorporation from ATP into triphosphoinositide by almost 30 %. 3. Acetylcholine (0.05mM) increased significantly the loss of 32P from triphosphoinositide (the 'triphosphoinositide effect') in 32P-labelled iris muscle. This effect was measured both chemically and radiochemically. It was also observed when 32P1 was replaced by myo-[3H]inositol in the incubation medium.4. The triphosphoinositide effect was blocked by atropine but not by D-tubocurarine. Further, muscarinic but not nicotinic agonists were found to provoke this effect. 5. Acetylcholine decreased by 28% the 32p incorporation into triphosphoinositide, presumably by stimulating its breakdown. This decrement in triphosphoinositide was blocked by atropine, but not by D-tubocurarine. 6. The triphosphoinositide effect was accompanied by a significant increase in 32p labelling, but not tissue concentration, of phosphatidylinositol and phosphatidic acid. The possible relationship between the loss of 32p label from triphosphoinositide in response to acetylcholine and the concomitant increase in that of phosphatidylinositol and phosphatidic acid is discussed. 7. The presence of triphosphoinositide phosphomonoesterase, the enzyme that might be stimulated in the iris smooth muscle by the neurotransmitter, was demonstrated, and, under our methods of homogenization and assay, more than 80% of its activity was localized in the particulate fraction.

Synthesis and function of membrane phosphoinositides in budding yeast, Saccharomyces cerevisiae

“…The archetypical PtdIns [4,5]P 2 -initiated signal transduction pathway [27] involves hydrolytic degradation of PtdIns [4,5]P 2 by a receptor-stimulated phospholipase C (PLC) in response to external stimuli [28][29][30][31][32], thereby generating two second messengers: 1,2-diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (Ins [1,4,5]P 3 ). In animal cells, DAG activates certain isoforms of protein kinase C (PKC) [33][34][35], ultimately leading to changes in gene expression, whereas Ins[1,4,5]P 3 (IP3) binds to a group of intracellular receptors that interact with calcium channels, causing the release of Ca 2+ from intracellular stores [33,[36][37][38][39], triggering Ca 2+ -dependent responses.…”

Effects of Isoproterenol Pretreatment on Phosphatidylinositol Turnover in Rat Parotid Gland

“…1). Similar rapid increase in the radioactivity of phosphatidic acid has been observed in iris muscle after acetylcholine (25) and in isolated stomach smooth muscle cells after carbamyl choline exposure (26). Of particular interest in this connection is the recent finding that phosphatidic acid behaves as a Ca2+ ionophore, and it was suggested that phosphatidic acid may play some important roles in the activation of Ca2+ influx into smooth muscle cells (26,27).…”

Inositol phospholipid and phosphatidic acid metabolism in response to membrane receptor activation

“…More direct evidence of receptor-linked polyphosphoinositide breakdown was provided by Abdel-Latif et al (1977) for iris muscle and by Kirk et al (1981) for hepatocytes. Until quite recently, however, most workers considered that PtdIns was the lipid which responded.…”