scholarly journals Enhanced phosphatidylinositol labelling in rat parotid fragments exposed to α-adrenergic stimulation

1974 ◽  
Vol 138 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Robert H. Michell ◽  
Lynne M. Jones
Keyword(s):  
Parotid Gland ◽  
Blocking Agent ◽  
Phospholipid Metabolism ◽  
Adrenergic Agonists ◽  
Adrenergic Stimulation ◽  
Receptor Blocking ◽  
Rat Parotid Gland ◽  
Rat Parotid ◽  
Β Receptor ◽  
Stimulation Of

1. Adrenergic agonists provoke a marked increase in labelling of phosphatidylinositol in fragments of rat parotid gland. 2. Adrenaline and phenylephrine (an adrenergic α-agonist) are effective stimulants, but isoprenaline (an adrenergic β-agonist) is relatively ineffective. 3. The response evoked by phenylephrine or adrenaline is prevented by prior incubation of the tissue with phenoxybenzamine (an α-receptor blocking agent), but not by prior incubation with pindolol (a β-receptor blocking agent). 4. Adrenergic stimulation of phosphatidylinositol metabolism in parotid gland is therefore mediated through α-receptors, in common with the adrenaline-induced K+ efflux. It is not linked to enzyme secretion, which is triggered by stimulation of β-receptors. 5. It is suggested that the stimulation of phospholipid metabolism that occurs in several other tissues in the presence of adrenaline or noradrenaline may also involve α-receptors.

scholarly journals Horseradish peroxidase: factors affecting its distribution after retrograde infusion into the rat parotid gland.

1985 ◽  
Vol 33 (9) ◽  
pp. 942-950 ◽  
Author(s):  
M R Mazariegos ◽  
A R Hand
Keyword(s):  
Horseradish Peroxidase ◽  
Parotid Gland ◽  
Tight Junctions ◽  
Product Inhibition ◽  
Adrenergic Stimulation ◽  
Immunofluorescent Localization ◽  
Cytoplasmic Staining ◽  
Factors Affecting ◽  
Rat Parotid Gland ◽  
Rat Parotid

Previous studies have shown that tight junctions of the unstimulated rat parotid gland are impermeable to retrogradely administered tracers such as myoglobin. Permeability is increased following beta-adrenergic stimulation, allowing the tracers to reach the intercellular and interstitial spaces. Reaction product of retrogradely infused horseradish peroxidase (HRP) and lactoperoxidase in found in the intercellular and interstitial spaces in both resting and stimulated glands, and many acinar and duct cells contain diffuse cytoplasmic reaction product. In this study we investigate several factors that might influence the distribution of HRP in the parotid gland. Tracer distribution was similar with HRP obtained from different suppliers, with different HRP preparations (Sigma types II, VI, VIII, and IX), and at HRP concentrations of 0.1-10 mg/ml. Inclusion of various saccharides in the infusion solution had no effect on the distribution of reaction product. Inhibition of the enzymatic activity of HRP by extraction of the heme group or reaction with hydrazine reduced but did not eliminate the extraluminal and cytoplasmic reaction product. In contrast, HRP treated with high H2O2 concentrations (0.04 M) was retained in the lumina and cytoplasmic staining was nearly abolished. Immunofluorescent localization of untreated and H2O2-treated HRP after retrograde infusion confirmed the findings obtained using diaminobenzidine procedures. These results suggest that the peroxidatic activity of HRP may damage cell membranes and tight junctions in the rat parotid gland, and indicate that permeability studies employing HRP as a tracer should be interpreted with caution.

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 Lithium-induced reduction in intracellular inositol supply in cholinergically stimulated parotid gland

1986 ◽  
Vol 234 (1) ◽  
pp. 199-204 ◽  
Author(s):  
C P Downes ◽  
M A Stone
Keyword(s):  
Parotid Gland ◽  
Acinar Cells ◽  
Phospholipid Metabolism ◽  
Cholinergic Stimulation ◽  
Inositol Phosphatase ◽  
Agonist Stimulation ◽  
Rat Parotid Gland ◽  
Inositol Phospholipid ◽  
Rat Parotid ◽  
Phosphatidylinositol 4

The effects of lithium and cholinergic stimulation on inositol phospholipid metabolism have been assessed using rat parotid gland slices and isolated acinar cells labelled with 32Pi. Cholinergic stimulation using carbachol caused substantial breakdown of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) and enhanced labelling of phosphatidate (PA) and phosphatidylinositol (PtdIns). Lithium alone had little effect upon 32Pi incorporation, but in combination with carbachol it greatly reduced the PtdIns labelling response to the agonist. Instead the label accumulated in a lipid identified as cytidine monophosphorylphosphatidate. There was also an enhancement of the PA labelling response to carbachol. These lithium-induced alterations in agonist-stimulated phospholipid metabolism were reversed if 10-30 mM-inositol was included in the incubation medium. Despite reduced PtdIns synthesis, lithium had relatively little effect on polyphosphoinositide labelling in stimulated cells. Resynthesis of polyphosphoinositides was monitored in acinar cells that had been stimulated with carbachol and then treated with atropine to block muscarinic receptors. Treatment with lithium during the carbachol-stimulation phase reduced the rate of phosphatidylinositol 4-phosphate synthesis, but had no significant effect upon PtdInsP2. The results suggest that an active inositol phosphatase pathway is essential to maintain intracellular inositol levels, but that PtdInsP2 synthesis is not markedly reduced by a substantial fall in intracellular inositol. This implies a close control over the rates of PtdInsP2 breakdown and resynthesis during agonist stimulation.

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