scholarly journals The relationship of calcium to receptor-controlled stimulation of phosphatidylinositol turnover. Effects of acetylcholine, adrenaline, calcium ions, cinchocaine and a bivalent cation ionophore on rat parotid-gland fragments

1975 ◽  
Vol 148 (3) ◽  
pp. 479-485 ◽  
Author(s):  
L M Jones ◽  
R H Michell
Keyword(s):  
Parotid Gland ◽  
De Novo ◽  
Head Group ◽  
Ionophore A23187 ◽  
Bivalent Cation ◽  
Phosphatidylinositol Turnover ◽  
Rat Parotid Gland ◽  
Muscarinic Cholinergic ◽  
Rat Parotid ◽  
Stimulation Of

The possibility that Ca2+ ions are involved in the control of the increased phosphatidylinositol turnover which is provoked by alpha-adrenergic or muscarinic cholinergic stimulation of rat parotid-gland fragments has been investigated. Both types of stimulation provoked phosphatidylinositol breakdown, which was detected either chemically or radiochemically, and provoked a compensatory synthesis of the lipid, detected as an increased rate of incorporation of 32Pi into phosphatidylinositol. Acetylcholine had little effect on the incorporation of labelled glycerol, whereas adrenaline stimulated it significantly, but to a much lower extent than 32P incorporation: this suggests that the response to acetylcholine was entirely accounted for by renewal of the phosphorylinositol head-group of the lipid, but that some synthesis de novo was involved in the response to adrenaline. The responses to both types of stimulation, whether measured as phosphatidylinositol breakdown or as phosphatidylinositol labelling, occurred equally well in incubation media containing 2.5 mm-Ca2+ or 0.2 mm-EGTA [ethanedioxybis(ethylamine)-tetra-acetic acid]. Incubation with a bivalent cation ionophore (A23187) led to a small and more variable increase in phosphatidylinositol labelling with 32Pi, which occurred whether or not Ca2+ was available in the extracellular medium: this was not accompanied by significant phosphatidylinositol breakdown. Cinchocaine, a local anaesthetic, produced parallel increases in the incorporation of Pi and glycerol into phosphatidylinositol. This is compatible with its known ability to inhibit phosphatidate phosphohydrolase (EC 3.1.3.4) and increase phosphatidylinositol synthesis de novo in other cells. These results indicate that the phosphatidylinositol turnover evoked by alpha-adrenergic or muscarinic cholinergic stimuli in rat parotid gland probably does not depend on an influx of Ca2+ into the cells in response to stimulation. This is in marked contrast with the K+ efflux from this tissue, which is controlled by the same receptors, but is strictly dependent on the presence of extracellular Ca2+. The Ca2+-independence of stimulated phosphatidylinositol metabolism may mean that it is controlled through a mode of receptor function different from that which controls other cell responses. Alternatively, it can be interpreted as indicating that stimulated phosphatidylinositol breakdown is intimately involved in the mechanisms of action of alpha-adrenergic and muscarinic cholinergic receptor systems.

scholarly journals Cholinergically stimulated phosphatidylinositol breakdown in parotid-gland fragments is independent of the ionic environment

1976 ◽  
Vol 158 (2) ◽  
pp. 505-507 ◽  
Author(s):  
L M Jones ◽  
R H Michell
Keyword(s):  
Parotid Gland ◽  
Cyclic Nucleotides ◽  
Direct Interaction ◽  
Cholinergic Receptor ◽  
Receptor System ◽  
Muscarinic Cholinergic Receptor ◽  
Rat Parotid Gland ◽  
Sucrose Medium ◽  
Muscarinic Cholinergic ◽  
Rat Parotid

Carbamoylcholine stimulated phosphatidylinositol breakdown in rat parotid-gland fragments incubated in either a Krebs--Ringer medium or an ion-depleted iso-osmotic sucrose medium. This suggest that phosphatidylinositol breakdown is not initiated by a change in the intracellular concentration of Na+ or of K+, and previous experiments have already indicated that it is independent of cyclic nucleotides and Ca2+. Thus it seems that this reaction may be initiated by a direct interaction at the plasma membrane between the activated muscarinic cholinergic receptor system and the enzyme that catalyses phosphatidylinositol breakdown.

scholarly journals Breakdown of phosphatidylinositol provoked by muscarinic cholinergic stimulation of rat parotid-gland fragments

1974 ◽  
Vol 142 (3) ◽  
pp. 583-590 ◽  
Author(s):  
Lynne M. Jones ◽  
Robert H. Michell
Keyword(s):  
Lipid Metabolism ◽  
Cholinergic Stimulation ◽  
Muscarinic Cholinergic Receptors ◽  
The Past ◽  
Rat Parotid Gland ◽  
Muscarinic Cholinergic ◽  
High Concentrations ◽  
Rat Parotid ◽  
Stimulation Of

When rat parotid fragments that had been labelled with32P in vivo were exposed to high concentrations of acetylcholine, radioactivity was lost from phosphatidylinositol but not from other phospholipids. Simultaneously the concentration of phosphatidylinositol in the tissue decreased. If previously unlabelled tissue was incubated with32Pi an increase in incorporation of radioactivity into phosphatidylinositol was observed during this decrease in concentration. The effects of acetylcholine were blocked by atropine, but not by tubocurarine. The response to acetylcholine was rapid, with up to one-third of the tissue's phosphatidylinositol disappearing within 5min. Similar effects were evoked by stimulation with methacholine and by high concentrations of tetramethylammonium ion; these responses were also atropine-sensitive and tubocurarine-insensitive. It is concluded that the event in inositol lipid metabolism that is affected by acetylcholine stimulation is removal of the phosphorylinositol group from the molecule; this is mediated through muscarinic cholinergic receptors. This is followed by a compensatory increase in the rate of synthesis of phosphatidylinositol, which has been described in detail in the past. These observations are compared with those of previous workers and are discussed in relation to the existing hypotheses relating to the significance of stimulus-provoked phosphatidylinositol turnover.

scholarly journals Calcium-dependent inhibition of protein synthesis in rat parotid gland

1978 ◽  
Vol 176 (1) ◽  
pp. 23-29 ◽  
Author(s):  
P Kanagasuntheram ◽  
S C Lim
Keyword(s):  
Protein Synthesis ◽  
Parotid Gland ◽  
Ionophore A23187 ◽  
Phenylalanine Concentration ◽  
Calcium Dependent ◽  
Rat Parotid Gland ◽  
Inhibition Of Protein Synthesis ◽  
Dependent Inhibition ◽  
Rat Parotid

1. Protein synthesis in the rat parotid gland in vitro was studied by measuring the incorporation of [3H]phenylalanine into trichloroacetic acid-insoluble proteins. In the unstimulated gland, the rate of incorporation was dependent on the phenylalanine concentration in the medium and proceeded linearly for up to 3h. 2. Adrenaline, carbamoylcholine, phenylephrine and ionophore A23187 inhibited the incorporation of [3H]phenylalanine into acid-insoluble protein; isoprenaline, dibutyryl cyclic AMP and 8-bromo-cyclic GMP were inactive. 3. Inhibition by adrenaline and carbamoylcholine but not by ionophore A23187 required extracellular Ca2+. 4. Both adrenaline and carbamoylcholine increased the magnitude of the acid-soluble [3H]phenylalanine pool at 10 micrometer extracellular phenylalanine, but had no effect if the phenylalanine concentration was increased to 200 micrometer. 5. There was no correlation between cellular ATP content and the observed inhibition of protein synthesis. 6. Our results suggest that both alpha-adrenergic and cholinergic receptors may play a role in the regulation of protein synthesis in the rat parotid gland, and that their effects are mediated by a rise in intracellular free Ca2+.

Sign in / Sign up

Export Citation Format

Share Document