Enhanced phosphatidylinositol labelling in rat parotid fragments exposed to alpha-adrenergic stimulation.
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ABSTRACT:
SUBMITTER: Michell RH
PROVIDER: S-EPMC1166173 | biostudies-other | 1974 Jan
REPOSITORIES: biostudies-other
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Project description:When rat parotid fragments that had been labelled with (32)P 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 with (32)P(i) 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.
| S-EPMC1168322 | biostudies-other
Project description:beta-Adrenergic stimulation of rat parotid acinar cells markedly increases [3H]mannose incorporation into N-linked glycoproteins [Kousvelari, Grant, Banerjee, Newby & Baum (1984) Biochem. J. 222, 17-24]. More than 90% of this protein-bound [3H]mannose was preferentially incorporated into four secretory glycoproteins. The ratio of [3H]mannose/[14C]leucine present in these individual proteins was 1.7-4-fold greater with isoproterenol-treated cells than with untreated controls. In isoproterenol-stimulated cells, [3H]mannose incorporation into mannosylphosphoryl dolichol and oligosaccharide-PP-dolichol was increased 2-3-fold over that observed in unstimulated cells. Similarly, formation of mannosylated oligosaccharide-PP-dolichol was increased approx. 4-fold in microsomes prepared from isoproterenol-treated cells. Also, turnover of oligosaccharide-PP-dolichol was significantly increased (5-fold) by beta-adrenergic stimulation; the half-life for oligosaccharide-PP-dolichol decreased from 6 min in control cells to 1.2 min in isoproterenol-stimulated cells. By 15 min after isoproterenol addition to acinar cells, the specific radioactivity of parotid oligosaccharide moieties increased about 3-fold over the value observed in the absence of the agonist. Taken together, these results strongly suggest that elevation of N-linked protein glycosylation in rat parotid acinar cells after beta-adrenoreceptor stimulation resulted from significant enhancement in the synthesis of mannosylphosphoryl dolichol and oligosaccharide-PP-dolichol and the turnover of oligosaccharide-PP-dolichol.
| S-EPMC1152764 | biostudies-other
Project description:1. The alpha-adrenergic agonists noradrenaline (in the presence of beta-blocker) and phenylephrine cause a transient stimulation of the respiration in isolated rat hepatocytes. After a lag period of 12s, this activation first attains its maximal value (+24%) for about 1 min and then falls to a sustained value (+15%). The effect is blocked by the alpha-antagonists phenoxybenzamine and phentolamine. It is dose-dependent, with an half-maximal stimulation by 16 nM-noradrenaline, which is similar to that found for other cell responses to the hormone. 2. Vasopressin and ATP, which in common with alpha-agonists are believed to increase intracellular [Ca2+], induce similar activation in the respiration rate. 3. The alpha-adrenergic-mediated respiration depends on extracellular Ca2+. The activation is decreased or abolished when extracellular [Ca2+] is decreased by adding EGTA, or when the Ca2+ antagonists Mn2+ and La3+ are present in the incubation medium. 4. It is suggested that the activation of the mitochondrial respiration rate results from the increase in cytosolic Ca2+ concentration, presumably via Ca2+ influx or Ca2+ release from the plasma membrane or endoplasmic reticulum.
| S-EPMC1154301 | biostudies-other
Project description:1. Rat cerebral-cortex slices were incubated with (32)P(i), acetylcholine and eserine for periods of 10min and 2h. The specific radioactivity of phosphatidylinositol was elevated during these treatments by 36 and 106% respectively. 2. The specific radioactivities of the phosphatidylinositol in different cell structures were determined after subcellular fractionation. They were highest in the nuclear, microsomal and synaptic-vesicle fractions and lowest in myelin, both in the controls and in the acetylcholine-treated slices. 3. The stimulated labelling of phosphatidylinositol was relatively evenly distributed: no subcellular fraction showed a stimulation markedly higher than that in the homogenate. 4. Studies of the distributions and activities of marker enzymes indicated that the subcellular fractionation achieved was similar to that with fresh tissue. 5. The results are discussed in relation to the previous report that the stimulation is observed throughout the neuronal cell-bodies and in relation to the hypothesis that the labelled phosphatidylinositol produced by stimulation is a component of an acetylcholine-receptor proteolipid localized in the synaptic junction.
| S-EPMC1178537 | biostudies-other
Project description:The mechanisms by means of which phenylephrine stimulates glutamine metabolism were studied in isolated rat hepatocytes. In the first 2 min after phenylephrine addition there was a rapid fall in the concentrations of intracellular 2-oxoglutarate and glutamate, presumably owing to activation of 2-oxoglutarate dehydrogenase. This was followed 2-3 min later by activation of glutaminase and by increases in glutamate and 2-oxoglutarate. Activation of glutaminase by phenylephrine was due to direct stimulation of the enzyme rather than to reversal of inhibition by the decrease in 2-oxoglutarate and glutamate. The stimulation of glutaminase by phenylephrine is partly due to an increase in the affinity of the enzyme for ammonia, its essential activator. It is concluded that stimulation of steady-state flux through the pathway from glutamine to glucose and urea can only be achieved by stimulation of glutaminase, the first enzyme in the pathway.
| S-EPMC1152637 | biostudies-other
Project description:Hemin is an activator of heme oxygenase-1 (HO-1), an enzyme catalyzing heme degradation. Up-regulation of HO-1 is observed in response to various pathological conditions. Moreover, pharmacological activation of HO-1 is associated with numerous beneficial effects in the organism. Hemin was shown to exert, among other, anti-diabetic and anti-obesity properties. These effects are strongly linked with adipose tissue. However, the direct influence of hemin on metabolism of the fat cells have not been explored. The present study aimed to determine the short-term effects of hemin on metabolism of the primary rat adipocytes. We focused on processes directly related to lipid accumulation, such as lipogenesis and lipolysis. For this purpose, the isolated cells were subjected for 2 h to 40 µM hemin, and effects of this compound on insulin-stimulated glucose conversion to lipids, lactate release, lipolysis induced by various stimuli, and also on the antilipolytic action of insulin were determined. It was shown that hemin did not affect insulin-induced lipogenesis and lactate release. However, hemin significantly decreased lipolysis stimulated by epinephrine. The inhibitory effect of hemin on epinephrine-induced lipolysis was not abolished in the presence of SnMP, an inhibitor of HO-1, which suggests hemin action irrespective of this enzyme. Similar inhibitory effects on epinephrine-induced lipolysis were observed in the presence of 3 and 12 mM glucose. Moreover, hemin was shown to reduce epinephrine-induced lipolysis also when glucose was replaced by alanine or by succinate. Apart from changes in epinephrine action, it was found that the lipolytic response of the adipocytes to isoproterenol was also diminished by hemin. However, hemin failed to affect lipolysis stimulated by dibutyryl-cAMP (a direct activator of protein kinase A), forskolin (an activator of adenylate cyclase), and also by DPCPX (an adenosine A1 receptor antagonist). Additionally, epinephrine-induced lipolysis was shown to be decreased by insulin, and this effect was deepened in the presence of hemin. These results indicate that short-term exposure of the adipocytes to hemin does not affect processes related to glucose metabolism, such as lipogenesis and lactate release. However, hemin was found to decrease the lipolytic response to adrenergic stimulation, which is associated with reduced lipid release from adipocytes. Moreover, our results indicate that hemin is also capable of diminishing the exaggerated lipolysis, which occurs in the presence of supraphysiological concentrations of glucose.
| S-EPMC8418796 | biostudies-literature
Project description: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.
| S-EPMC1165566 | biostudies-other
Project description:Mammalian cardiac myocytes become postmitotic shortly after birth, and the subsequent myocardial growth in adaptation to increasing workloads becomes primarily dependent on hypertrophy of existing myocytes. Although hypertrophic growth of cardiac myocytes has been extensively studied by using both in vitro and in vivo models, the molecular mechanism controlling the switch from hyperplastic to hypertrophic growth of cardiac myocytes is largely unknown. Since the majority of terminally differentiated cardiac myocytes are growth-arrested in G1/G0 phase, it has been hypothesized that the retinoblastoma protein (Rb) or its related pocket proteins which block G1/S transition becomes constitutively active during myocardial terminal differentiation. To test this hypothesis, we studied the regulation of Rb activity by alpha-adrenergic stimulation in neonatal rat ventricular myocytes which are mostly postmitotic in culture. Our results demonstrate that Rb is predominantly in the active hypo-phosphorylated state in control neonatal ventricular myocytes. alpha-Adrenergic stimulation activates G1/S transition in foetal but not neonatal rate ventricular myocytes. Although alpha-adrenergic stimulation does not activate G1/S transition in neonatal myocytes, it induces hyperphosphorylation of Rb to the same extent as in proliferating skeletal-muscle myoblasts or foetal ventricles. Hyper- but not hypo-phosphorylated Rb in stimulated neonatal myocytes or proliferating skeletal-muscle myoblasts fails to bind to the transcription factor, E2F, suggesting that hyper-phosphorylated Rb is inactive. Therefore F1/S transition could also be blocked at steps in addition to Rb inactivation during terminal differentiation and these blockades are refractory to alpha-adrenergic stimulation.
| S-EPMC1218794 | biostudies-other
Project description: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.
| S-EPMC1163998 | biostudies-other
Project description:In mammals, increasing evidence supports the generality of cotranscriptional gene regulation and the idea that genetic control often occurs subsequent to RNA polymerase II (Pol II) recruitment. In our recent experiments, we have used Pol II Chromatin Immunoprecipitation (ChIP) to investigate relationships between the mechanistic events that control acute stress response (ASR) gene activation following stimulation of the alpha1a-Adrenergic Receptor expressed in rat-1 fibroblasts. We validate the temporal accuracy of our Pol II ChIP assay by comparison to major transcriptional events assessable by microarray and PCR analysis of precursor and mature mRNA. Initial temporal microarray analysis of gene activation following agonist addition identified genes that were upregulated and provided a temporal profile of changes in polyadenylated mRNA levels. Combined with PCR analysis of pre-mRNA, total RNA, polyadenylated RNA and the Pol II ChIP data, we demonstrate complex multilevel gene regulation including a diverse set of cotranscriptional mechanisms. Given our data, we propose that analysis of a genes regulation must begin with global assessement of changes in transcriptional behavior to identify events that are actually rate limiting if reductionist mechanistic dissection is to distinguish events that are regulated from the larger set of mechanisms available to most genes. This microarray analysis reports on the temporal changes in polyadenylated mRNA levels in proliferating rat-1 fibroblasts following stimulation of the alpha-1a Adrenergic Receptor with filter sterilized 10 uM phenylephrine (PE). Cells were treated and harvested at 70 to 80% confluence. Rat-1 cells under these conditions are still mid-log phase and continue to proliferate for at least another replicative cycle. Message levels in untreated cells were determined for 3 biological replicates, but all other time points are single replicates as sufficiently detailed dissection made replicates expensive and unnecessary, given that clear trending behavior in the expression profiles demonstrates profile accuracy.
2014-08-01 | E-GEOD-59955 | biostudies-arrayexpress