UMLS:C0043167 - FACTA Search

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Query: UMLS:C0043167 (pertussis)
19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The intracellular signals generated by carbachol activation of the muscarinic receptor [release of inositol phosphates as a consequence of phosphoinositide hydrolysis and rise of the cytosolic Ca2+ concentration ([Ca2+]i, measured by quin2)] were studied in intact PC12 pheochromocytoma cells that had been differentiated by treatment with nerve growth factor. When measured in parallel samples of the same cell preparation 30 s after receptor activation, the release of inositol trisphosphate and of its possible metabolites, inositol bis- and mono-phosphate, and the [Ca2+]i rise were found to occur with almost superimposable carbachol concentration curves. At the same time carbachol caused a decrease in the radioactivity of preloaded phosphatidylinositol 4,5-bisphosphate, the precursor of inositol trisphosphate. Neither the inositol phosphate nor the [Ca2+]i signal was modified by preincubation of the cells with either purified Bordetella pertussis toxin or forskolin, the direct activator of adenylate cyclase. Both signals were partially inhibited by dibutyryl cyclic AMP, especially when the nucleotide analogue was applied in combination with the phosphodiesterase inhibitors RO 201724 and theophylline. The latter drug alone profoundly inhibited the carbachol-induced [Ca2+]i rise, with only minimal effect on phosphoinositide hydrolysis. Because of the diverging results obtained with forskolin on the one hand, dibutyryl cyclic AMP and phosphodiesterase inhibitors on the other, the effects of the latter drugs are considered to be pharmacological, independent of the intracellular cyclic AMP concentration. Two further drugs tested, mepacrine and MY5445, inhibited phosphoinositide hydrolysis at the same time as the 45Ca2+ influx stimulated by carbachol. Taken together, our results concur with previous evidence obtained with permeabilized cells and cell fractions to indicate phosphatidylinositol 4,5-bisphosphate hydrolysis and [Ca2+]i rise as two successive events in the intracellular transduction cascade initiated by receptor activation. The strict correlation between the carbachol concentration curves for inositol trisphosphate generation and [Ca2+]i rise, and the inhibition by theophylline of the Ca2$ signal without major effects on inositol phosphate generation, satisfy important requirements of the abovementioned interpretation.
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PMID:Activation of muscarinic receptors in PC12 cells. Correlation between cytosolic Ca2+ rise and phosphoinositide hydrolysis. 301 59

A wide variety of receptors appear to be coupled to a phospholipase C (EC 3.1.4.3) that hydrolyzes inositol lipids. This reaction is believed to provide a link between receptor activation and cellular Ca2+ mobilization. The mechanisms by which this occurs are believed to involve inositol 1,4,5-trisphosphate (1,4,5-IP3), which signals release of Ca2+ from the endoplasmic reticulum. In rat parotid acinar cells made permeable with saponin, 1,4,5-IP3 induced rapid release of sequestered Ca2+. In intact parotid cells, the concentration-response relationship for methacholine-induced IP3 formation was similar to the relationship for muscarinic receptor occupancy by methacholine. About 10-fold lower concentrations of methacholine were sufficient to increase cytosolic [Ca2+] and to activate secretion, indicating an excess IP3 forming capacity for the muscarinic receptor. The mechanisms for the coupling of receptors to IP3 formation were studied in pancreatic acinar cells made permeable electrically. In this preparation, nonhydrolyzable derivatives of GTP potentiated agonist-induced IP3 production, which suggests the involvement of a guanine nucleotide-dependent regulatory protein. The effects of agonists and guanine nucleotides were not altered by pretreating the acinar cells with cholera or pertussis toxins, which indicated that the regulatory protein linking receptors to IP3 formation is distinct from the ones involved in the regulation of adenylate cyclase.
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PMID:Formation and biological action of inositol 1,4,5-trisphosphate. 301 83

In an attempt to identify the nature of guanine nucleotide binding protein(s) (G-protein) involved in the acetylcholine (ACh)-induced (muscarinic) response of pig coronary-artery smooth muscle, we studied the effect of ADP-ribosylation of specific membrane protein(s) catalysed by islet-activating protein (IAP; pertussis toxin). The ACh-stimulated and guanine nucleotide-dependent activities of phosphatidylinositol 4,5-bisphosphate (PIP2) phosphodiesterase (PDE), assessed by the production of inositol 1,4,5-trisphosphate (IP3) from exogenously applied PIP2, were not modified, in either IAP-treated or non-treated cell homogenates used as the enzyme source. In intact tissues, pretreatment with up to 100 ng of IAP/ml inhibited neither the ACh-induced decrease in the amount of inositol phospholipids nor the increase in the amounts of phosphatidic acid and of inositol phosphates. IAP treatment increased the amount of cyclic AMP accumulated by isoprenaline. These observations suggest that G-protein which couples the muscarinic receptor to PIP2-PDE is insensitive to IAP. Such being the case, the nature of this protein(s) probably differs from that required for the regulation of adenylate cyclase activities (Ni or Gi).
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PMID:Guanine nucleotide binding protein involved in muscarinic responses in the pig coronary artery is insensitive to islet-activating protein. 303 Feb 65

Treatment with pertussis toxin not only prevents inhibitory effects (e.g., reduced adenylate cyclase activity, decreased voltage-dependent Ca2+ entry, increased K+ efflux, and negative inotropy) but also unmasks stimulant effects (e.g., membrane depolarization and positive inotropy) of carbachol in chick atria. Pertussis toxin prevents transducer proteins (Ni and No) from linking muscarinic receptors to either adenylate cyclase and Ca2+ channels or K+ channels. However, pertussis toxin treatment does not block N proteins linking the muscarinic receptor to stimulant membrane effects. Membrane depolarization by carbachol, attributed by others to increased Na+ entry, may stimulate Na-Ca exchange and positive inotropy, perhaps by activation of phospholipase D. Alternatively, carbachol could increase inositol triphosphate content and thereby release Ca2+ from the sarcoplasmic reticulum to increase the force of contraction. The ability of carbachol to increase phosphoinositide hydrolysis is resistant to pertussis toxin. The second-messenger role of phospholipid metabolites provides a foundation for testing the hypothesis that such metabolites are eventually involved in the stimulant actions of carbachol seen in pertussis toxin-treated preparations.
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PMID:Positive vs. negative inotropic effects of carbachol in avian atrial muscle: role of Ni-like protein. 311 21

Purified porcine atrial muscarinic receptor (mAcChR) was reconstituted with purified porcine atrial inhibitory guanine nucleotide binding protein (Gi) in a lipid mixture consisting of phosphatidylcholine, phosphatidylserine, and cholesterol (1:1:0.1 w/w). 5'-Guanylyl imidodiphosphate (0.1 mM) had no effect on the binding of the muscarinic antagonist L-quinuclidinyl benzilate but converted high-affinity carbachol binding sites (Kd equal to 1 microM) in the reconstituted preparation to the low-affinity state (Kd equal to about 100 microM). Steady-state kinetic measurements of GTPase activity showed that the turnover number was increased from 0.19 min-1 in the presence of the muscarinic antagonist L-hyoscyamine to 2.11 min-1 for the agonist carbachol. The affinity of Gi for GDP was reduced by about 50-fold upon interaction with the carbachol-mAcChR complex, and the observed rate constant for GDP dissociation was increased by 38-fold from 0.12 to 4.5 min-1. Thus, the increase in steady-state GTPase activity observed for muscarinic agonists is largely, if not exclusively, due to the increase in GDP dissociation from Gi--probably the rate-limiting step in the steady-state mechanism. Carbachol-stimulated GTPase was sensitive to ADP-ribosylation of the reconstituted Gi by pertussis toxin, but the high-affinity agonist binding was uncoupled only when the reconstituted preparation was treated with pertussis toxin in the presence of GTP and the agonist acetylcholine. These results suggest that association with the mAcChR protects Gi from ADP-ribosylation by pertussis toxin.
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PMID:Reconstitution of the purified porcine atrial muscarinic acetylcholine receptor with purified porcine atrial inhibitory guanine nucleotide binding protein. 312 98

Cultures of myocytes from embryonic chick atria grown in medium supplemented with fetal calf serum from which lipoproteins had been removed demonstrated a nearly 10-fold increase in sensitivity of beating to the muscarinic cholinergic agonist carbamylcholine compared to cells grown with control serum. This effect was reversed by growth of cells in medium supplemented with lipoprotein-depleted serum (LPDS) reconstituted with the low density lipoprotein fraction from fetal calf serum. In cells grown in LPDS, total cell cholesterol was increased 32% over control levels and returned to control levels in cells grown with LPDS reconstituted with low density lipoprotein. Growth of cells in LPDS plus mevinolin, an inhibitor of endogenous cholesterol synthesis, also reversed the effects of LPDS on cholesterol content and sensitivity of beating to carbamylcholine. The ability of mevinolin (30 microM) to reverse the effect of LPDS on sensitivity of beating to carbamylcholine was inhibited by mevalonic acid, a metabolic precursor to cholesterol, with an IC50 of 7 x 10(-5) M. These data suggest that mevinolin reverses the effects of LPDS by altering cellular cholesterol levels. Enhanced responsiveness of embryonic chick heart cells to muscarinic stimulation was associated with a 2-fold increase in the number of muscarinic receptors with high affinity for agonist from 82 +/- 10 fmol/mg protein in media containing fetal calf serum to 175 +/- 12 fmol/mg protein in cells grown in the presence of LPDS. The distribution of receptors between high affinity (RH) and low affinity (RL) forms changed from 41% RH and 59% RL in cells grown in control serum to 66.5% RH and 33.5% RL in cells grown in LPDS. Quantitation of the effect of growth in LPDS on the levels of guanine nucleotide regulatory proteins No and Ni which couple the muscarinic receptor to a physiologic response, demonstrated that the relative levels of the 39-kDa alpha subunits of No and 41-kDa alpha subunits of Ni determined by ADP ribosylation with pertussis toxin and immunoblotting increased 2-fold compared to control cells grown with fetal calf serum. Growth of cells with medium supplemented with LPDS plus mevinolin reduced the levels of alpha 39 and alpha 41 to below the levels in control cells. Levels of the beta subunit of No and Ni were unaffected by growth with LPDS.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effects of low density lipoproteins and mevinolin on cholesterol content and muscarinic cholinergic responsiveness in cultured chick atrial cells. Regulation of levels of muscarinic receptors and guanine nucleotide regulatory proteins. 313 73

The hippocampal slice preparation was used to classify cholinergic effects in terms of muscarinic receptor subtypes (M1 or M2) and biochemical effector systems linked to these effects in CA1 pyramidal cells. Based on the action of the M1 antagonist pirenzepine and the M2 antagonist gallamine, the muscarinic-induced membrane depolarization and blockade of the afterhyperpolarization appear to result from activation of an M1 receptor, while the cholinergic depression of the EPSP and the blockade of a potassium current termed the M-current appears to involve the activation of an M2 receptor. All of the muscarinic actions could be observed in pertussis toxin-treated hippocampi, suggesting that a pertussis toxin-sensitive G-protein is not involved in these actions. Cholinergic agents that are weak agonists of phosphoinositide (PI) turnover are fully effective in all of the muscarinic actions except the blockade of the M-current on which they had little agonist activity and actually blocked the action of full agonists. These results strongly suggest that the blockade of the M-current may involve stimulation of PI turnover. In addition, we show that the blockade of the M-current is mimicked by intracellular application of inositol trisphosphate. Our results do not show any obvious relationship between the muscarinic receptor subtypes and the biochemical effector systems.
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PMID:Classification of muscarinic responses in hippocampus in terms of receptor subtypes and second-messenger systems: electrophysiological studies in vitro. 314 94

The guanine nucleotide regulatory proteins, alpha i and alpha o, coexist in a variety of tissues, including heart, brain, and adipose tissues and are ADP-ribosylated by pertussis toxin (Gilman AG, G-proteins and dual control of adenylate cyclase. Cell 26: 577-579, 1984). Previous studies in which purified G proteins were reconstituted with cell membranes and/or phospholipid vesicles have suggested that an alpha i-like protein mediates GTP-dependent inhibition of adenylate cyclase activity. However, direct studies comparing the role of alpha i and alpha o in mediating the inhibition of adenylate cyclase activity in the intact cell have not appeared. In the present study, we demonstrated that, in the intact cell, alpha o was more sensitive to ADP-ribosylation in the presence of pertussis toxin than was alpha i. The T1/2 for pertussis toxin-mediated ADP-ribosylation of alpha i was 199 +/- 10 min (mean +/- SE, N = 10) compared to 157 +/- 7 min for alpha o. The IC50 for pertussis toxin-induced ADP-ribosylation of alpha i was 158 +/- 40 pg/ml (mean +/- SE, N = 11) compared to 35 +/- 8 pg/ml for alpha o. The differences in both T1/2 and IC50 for alpha i and alpha o were statistically significant (P less than 0.001). Studies were carried out to determine whether alpha o was involved in coupling the muscarinic cholinergic receptor to inhibition of adenylate cyclase activity in intact cells. The time course and dose dependence of the pertussis toxin-induced uncoupling of the muscarinic receptor from inhibition of adenylate cyclase closely paralleled the time course and dose dependence for the ADP-ribosylation of alpha i but differed significantly (P less than 0.001) from the time course and dose dependence for the ADP-ribosylation of alpha i but differed significantly (P less than 0.001) from the time course and dose dependence of the pertussis toxin mediated ADP-ribosylation of alpha o. The T1/2 and IC50 values for the pertussis toxin-induced decrease in the inhibition of adenylate cyclase activity were 210 +/- 6 min (mean +/- SE, N = 11) and 169 +/- 25 pg/ml (mean +/- SE, N = 12), respectively, which were not significantly different from the T1/2 and IC50 for pertussis toxin mediated ADP-ribosylation of alpha i. The data are consistent with the hypothesis that, in the intact cell, a pertussis toxin-sensitive alpha i-like protein, but not alpha o, couples muscarinic receptors to inhibition of adenylate cyclase activity.
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PMID:Differential sensitivity of alpha o and alpha i to ADP-ribosylation by pertussis toxin in the intact cultured embryonic chick ventricular myocyte. Relationship to the role of G proteins in the coupling of muscarinic cholinergic receptors to inhibition of adenylate cyclase activity. 314 83

Prior physiological studies have suggested that parasympathetic control is altered in heart failure. The goal of our studies was to investigate the influence of heart failure on the muscarinic receptor, and its coupling to adenylate cyclase. Ligand binding studies using [3H]quinuclidinyl benzilate and enriched left ventricular (LV) sarcolemma, demonstrated that muscarinic receptor density in heart failure declined 36% from a control of 5.6 +/- 0.6 pmol/mg, with no change in antagonist affinity. However, agonist competition studies with both carbachol and oxotremorine showed that it was a loss of high affinity agonist binding sites in the sarcolemma from failing LV that accounted for this difference. The functional efficacy of the muscarinic receptor was also examined. When 1 microM methacholine was added to 0.1 mM GTP and 0.1 mM isoproterenol, adenylate cyclase stimulated activity was inhibited by 15% in normal LV but only 5% in LV sarcolemma from animals with heart failure even when the reduced adenylate cyclase in these heart failure animals was taken into account. Even at 100-fold greater concentrations of methacholine, significantly less inhibition of adenylate cyclase activity was observed in LV failure as compared with normal LV sarcolemma. Levels of the GTP-inhibitory protein known to couple the muscarinic receptor to adenylate cyclase, as measured with pertussis toxin labeling, were not depressed in LV failure. Thus, the inhibitory pathway regulating LV adenylate cyclase activity is defective in heart failure. The decrease in muscarinic receptor density, and in particular the specific loss of the high affinity agonist binding component of this receptor population, appears to be the major factor underlying this abnormality.
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PMID:Impaired cardiac muscarinic receptor function in dogs with heart failure. 329 Feb 56

We have shown previously that stimulation of high-affinity GTP hydrolysis and inhibition of adenylate cyclase activity by muscarinic agonists are mediated by pertussis toxin (IAP) substrates (Gi and Go) in canine cardiac sarcolemma. We have now used the pertussis toxin-treated dog as a whole animal model in which Gi- and Go-mediated biochemical mechanisms can be studied. Mongrel dogs were injected intravenously with IAP 48 hours prior to death and isolation of left ventricular sarcolemma. Treatment of the animal in vivo with the toxin prevented subsequent in vitro IAP-catalyzed [32P]ADP-ribosylation of substrates in cardiac, erythrocytic, and renal cortical plasma membranes, suggesting that ADP-ribosylation occurred in vivo from endogenous substrate. Consistent with our previous results obtained by treating sarcolemma in vitro with IAP, muscarinic receptor-mediated stimulation of high-affinity GTP hydrolysis and inhibition of GTP-activated adenylate cyclase activity were attenuated in sarcolemma purified from the toxin-treated animals. Proximal to adenylate cyclase, guanine nucleotide regulation of muscarinic receptor affinity for agonists was also abolished in membranes from the toxin-treated animals. In addition, the ability of oxotremorine to attenuate GTP regulation of stimulation of adenylate cyclase activity by magnesium ions was abolished in sarcolemma from the IAP-treated dogs. Thus, cardiac sarcolemma isolated from the IAP-treated animals displayed biochemical characteristics of an adenylate cyclase system in which inhibitory regulatory pathways had been attenuated. The cardiac biochemical studies and the in vivo ADP-ribosylation of noncardiac IAP substrates also suggests considerable potential use of this model in the physiological and biochemical study of regulatory mechanisms mediated by GTP-binding proteins in other systems.
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PMID:Pertussis toxin-treated dog: a whole animal model of impaired inhibitory regulation of adenylate cyclase. 335 81

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