Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

G proteins couple receptors to ionic channels indirectly by acting on membrane enzymes which modulate channel activity through second or third messengers such as cytoplasmic kinases, IP3 or Ca++. Recently, it has been shown that G proteins can act on ionic channels in a membrane-delimited or direct manner; from our experience this phenomenon seems to be widespread. A G protein purified from human red blood cells (hRBC) Gk when preactivated with GTP gamma S acts directly on muscarinic acetylcholine receptor-regulated K+ channels (K+[ACh]) in atrial cells and the stimulatory regulator of adenylyl cyclase, Gs from hRBCs acts directly on two distinct voltage-gated Ca++ channels, one in cardiac muscle and the other in skeletal muscle T-tubules. In many cells, including clonal GH3 pituitary cells, somatostatin (SST) inhibits secretion by a complex mechanism that involves a pertussis toxin (PTX)-sensitive step. This is not due to lowering cAMP since secretion induced by cAMP analogs and K+ depolarization are also inhibited. SST also causes membrane hyperpolarization, which is similar to the effect of ACh on cardiac pacemaking cells and may lead to decreases in intracellular Ca++ needed for secretion. ACh acting through a muscarinic recpetor in GH3 cells has the same effects as SST.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Direct coupling of the somatostatin receptor to potassium channels by a G protein. 216 76

Topically applied acetylcholine elicited a hyperpolarizing (ACh-HP) response in about 2/3 of the principal neurons of rabbit superior cervical ganglia isolated in a culture medium for several days. Membrane changes responsible for the ACh-HP were multiple and varied with the level of membrane potential (Vm): At, or less negative than, resting Vm (about -60 mV), membrane conductance (Gm) was increased; at Vm more negative than -70 mV, Gm either increased, decreased, or remained unchanged. The effect of altering extracellular K+ and Ca2+ concentrations suggest that a Ca2(+)-dependent increase in K+ conductance contributes to ACh-HP; however, drugs reported to block such channels (D-tubocurarine at 30 microM or apamin at 200 nM) shortened duration of the ACh-HP but did not depress peak amplitude. The ACh-HP was depressed by the M2-muscarinic antagonist AF-DX 116 and blocked by an intracellular administration of guanosine-5'-o-(2-thiodiphosphate) (GDP-beta-S) or by preincubation with pertussis toxin. Intracellularly injected inositol-1,4,5-triphosphate (IP3) elicited a hyperpolarization associated with an increase in Gm at any Vms. Activators of protein kinase C applied extracellularly, 1,2-oleoylacetylglycerol (OAG) or phorbol-12,13-dibutyrate (Pb(Bu)2) elicited a hyperpolarization with a decrease in Gm at Vms more negative than -50 mV and a reversal potential close to Ec1. In the presence of Li+, ACh-HP was smaller after a repetitive stimulation with ACh. These results suggest that, in these neurons, ACh can directly activate M2-muscarinic receptors coupled to GTP-binding proteins, which leads to both an increase in Ca2(+)-sensitive K+ conductance mediated by the intracellular messenger IP3 and a decrease in a conductance, possibly Gc1, through another phosphatidylinositide pathway.
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PMID:Acetylcholine elicits metabolically mediated M2-muscarinic hyperpolarization in isolated rabbit sympathetic neurons. 239 36

The mechanism of muscarinic inhibition of the Ca-current (ICa) was studied in ventricular myocytes of guinea pig hearts and the following results were obtained. Acetylcholine (ACh) in concentrations up to 10(-4) M had little effect, if any, on ICa in control cells. ACh reduced the isoprenaline (ISP)-induced increase of ICa. The dose-response-relation (ISP concentration vs. ICa density) was shifted by ACh towards higher ISP concentrations. But both, at low and high ISP concentrations ACh had nor or little effect. ACh was ineffective when ICa was increased by dialysing the cell with catalytic subunit of cAMP-dependent protein kinase or cAMP. ACh reduced ICa enhanced by isobutylmethylxanthine or by forskolin. ACh did not depress ICa when the cell was dialysed with the non-hydrolysable GTP-derivative, GMP-PNP. In this condition the beta-adrenergic enhancement of ICa was also absent. Pertussis toxin, which is known to inhibit the inhibitory transducer protein (Ni), abolished the ACh response. We concluded from these results that ACh depresses ICa by inhibiting, via Ni, the cAMP production.
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PMID:On the mechanism of muscarinic inhibition of the cardiac Ca current. 242 6

The activation mechanisms of K+ channels by muscarinic acetylcholine (m-ACh) receptors were examined in isolated atrial cells by use of patch-recording technique. In "cell-attached" patch recordings, ACh, present in the pipette, activated an inwardly rectifying K+ channel. In "inside-out" patches, activation of the K+ channel by ACh diminished with time following excision of the patch, but it resumed when GTP was present in the solution bathing the intracellular side of the membrane. The A protomer of pertussis toxin, together with NAD, inhibited the channel activation in the presence of GTP. Since pertussis toxin specifically ADP-ribosylates GTP-binding proteins Ni and No, which can interact with m-ACh receptors, and inhibits their functions, it was concluded that m-ACh receptors communicate with the K+ channel via GTP-binding proteins, probably Ni and/or No, in atrial cell membrane.
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PMID:Acetylcholine activation of K+ channels in cell-free membrane of atrial cells. 242 58

The intracellular mechanisms by which cardiac Ca current (ICa) and the delayed outward K current (IK) are modulated during beta-adrenergic or muscarinic stimulation were investigated at the level of both single-channel and whole-cell currents in single ventricular myocytes of guinea-pigs. Superfusion of cells with beta-adrenergic agonist increased the amplitude of whole-cell ICa in a dose-dependent manner. In the single-channel recording, neither the amplitude of elementary current nor the total number of active channels was affected but the number of blank records was markedly reduced resulting in a larger amplitude of the ensemble average current. Intracellular dialysis of cells with cyclic AMP (cAMP) or the catalytic (C) subunit of cAMP-dependent protein kinase (cAMP-PK) produced a dose-dependent increase in the amplitude of ICa and IK. A non-hydrolysable ATP analogue, AMP-PNP, reduced whereas ATP gamma S enhanced the effects of beta-agonist on ICa and IK, suggesting an involvement of protein phosphorylation during the enhancement of these currents. The regulatory subunit of cAMP-PK, the heat-stable protein-kinase inhibitor (PKI) and type-1 protein phosphatase antagonized the beta-adrenergic enhancement of ICa and IK, but did not eliminate ICa. Acetylcholine (ACh) reduced the amplitude of ICa when ICa was enhanced by either beta-adrenergic agonist, forskolin or 3-isobutyl-1-methyl-xanthine but did ACh not when ICa was enhanced by intracellular dialysis with cAMP or C subunit, suggesting that muscarinic inhibition occurs at the level of adenylate cyclase. Non-hydrolysable GTP analogue, GMP-PNP, uncoupled both beta-adrenergic and muscarinic modulation of ICa. Pertussis toxin selectively eliminated the effect of ACh on ICa. Based on these results, we concluded that the activities of the Ca channel and the delayed outward K channel are controlled by the action of neurotransmitters, which are mediated by GTP-binding proteins and cAMP-dependent protein phosphorylation. It is suggested that phosphorylation of 'Ca-channel-related protein' leads to an increased open probability without changing the total number of channels or the elementary current amplitude.
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PMID:Intracellular control of calcium and potassium currents in cardiac cells. 243 80

Sympathetic neurons dissociated from the superior cervical ganglion of 2-day-old rats were studied by whole-cell patch clamp and by fura-2 measurements of the cytosolic free Ca2+ concentration, [Ca2+]i. Step depolarizations in the presence of tetrodotoxin and hexamethonium triggered two Ca2+ currents that differed in the voltage dependence of activation and kinetics of inactivation. These currents resemble the L and N currents previously described in chicken sensory neurons [Nowycky, M. C., Fox, A. P. & Tsien, R. W. (1985) Nature (London) 316, 440-442]. Treatment with acetylcholine resulted in the rapid (within seconds), selective, and reversible inhibition of the rapidly inactivated, N-type current, whereas the long-lasting L-type current remained unaffected. The high sensitivity to blocker drugs (atropine, pirenzepine) indicated that this effect of acetylcholine was due to a muscarinic M1 receptor. Intracellular perfusion with nonhydrolyzable guanine nucleotide analogs or pretreatment of the neurons with pertussis toxin had profound effects on the Ca2+ current modulation. Guanosine 5'-[gamma-thio]triphosphate caused the disappearance of the N-type current (an effect akin to that of acetylcholine, but irreversible), whereas guanosine 5'-[beta-thio]diphosphate and pertussis toxin pretreatment prevented the acetylcholine-induced inhibition. In contrast, cAMP, applied intracellularly together with 3-isobutyl-1-methylxanthine, as well as activators and inhibitors of protein kinase C, were without effect. Acetylcholine caused shortening of action potentials in neurons treated with tetraethylammonium to partially block K+ channels. Moreover, when applied to neurons loaded with the fluorescent indicator fura-2, acetylcholine failed to appreciably modify [Ca2+]i at rest but caused a partial blunting of the initial [Ca2+]i peak induced by depolarization with high K+. This effect was blocked by muscarinic antagonists and pertussis toxin and was unaffected by protein kinase activators. Thus, muscarinic modulation of the N-type Ca2+ channels appears to be mediated by a pertussis toxin-sensitive guanine nucleotide-binding protein and independent of both cAMP-dependent protein kinase and protein kinase C.
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PMID:Activation of a muscarinic receptor selectively inhibits a rapidly inactivated Ca2+ current in rat sympathetic neurons. 243 97

Arachidonic acid is released from cell membranes in response to receptor-dependent as well as receptor-independent stimulation in various cells, including cardiac myocytes. Arachidonic acid is converted to prostaglandins by cyclooxygenase and to leukotrienes by 5-lipoxygenase, metabolites which are very biologically active and modulate cellular functions such as platelet aggregation, smooth muscle contraction and neural excitation. The molecular mechanisms underlying their modulations are, however, still badly understood. Here, we report that the 5-lipoxygenase metabolites of arachidonic acid activate the pertussis toxin-sensitive G protein-gated muscarinic K+ channel (IK.ACh): arachidonic acid activation of IK.ACh was prevented by the lipoxygenase inhibitors, nordihydroguaiaretic acid and AA-861; leukotriene A4 and C4 activated IK.ACh. The activation occurred in pertussis toxin-treated atrial cells and ceased when inside-out patches were formed but the patches were still susceptible to stimulation by GTP and to inhibition by GDP-beta-S. These results indicate that arachidonic acid metabolites may stimulate the G-protein in a receptor-independent way.
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PMID:Arachidonic acid metabolites as intracellular modulators of the G protein-gated cardiac K+ channel. 249 39

Muscarinic receptors of cardiac pacemaker and atrial cells are linked to a potassium channel (IK.ACh) by a pertussis toxin-sensitive GTP-binding protein. The dissociation of G-proteins leads to the generation of two potential transducing elements, alpha-GTP and beta gamma. IK.ACh is activated by G-protein alpha- and beta gamma-subunits applied to the intracellular surface of inside-out patches of membrane. beta gamma has been shown to activate the membrane-bound enzyme phospholipase A2 in retinal rods. Arachidonic acid, which is produced from the action of phospholipase A2 on phospholipids, is metabolized to compounds which may act as second messengers regulating ion channels in Aplysia. Muscarinic receptor activation leads to the generation of arachidonic acid in some cell lines. We therefore tested the hypothesis that beta gamma activates IK.ACh by stimulation of phospholipase A2. When patches were first incubated with antibody that blocks phospholipase A2 activity, or with the lipoxygenase inhibitor, nordihydroguaiaretic acid, beta gamma failed to activate IK.ACh. Arachidonic acid and several of its metabolites derived from the 5-lipoxygenase pathway, activated the channel. Blockade of the cyclooxygenase pathway did not inhibit arachidonic acid-induced channel activation. We conclude that the beta gamma-subunit of G-proteins activates IK.ACh by stimulating the production of lipoxygenase-derived second messengers.
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PMID:G-protein beta gamma-subunits activate the cardiac muscarinic K+-channel via phospholipase A2. 249 40

A new GTP-binding protein, which serves as a substrate for pertussis toxin, was prepared from porcine brain. The new G protein was separated from other GTP-binding proteins, Gi and Go, by an anion-exchange column chromatography. The mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the alpha subunit of the new G protein was between those of alpha subunits of Gi and Go. Evidence that the alpha subunit is not a proteolytic fragment of the alpha subunit is not a proteolytic fragment of the alpha subunit of Gi or Go was provided by experiments involving partial hydrolysis of these G proteins with thermolysin and their interaction with an antibody raised against the amino terminal peptide of the alpha subunit of Gi. In addition, the gamma subunit of the new G protein was indicated to be different from the gamma subunits of Gi and Go, because the latter were found to be phosphorylated by protein kinase C but the former was not. GTP-sensitive high affinity binding of muscarinic receptors with acetylcholine was observed when muscarinic receptors purified from porcine cerebrum were reconstituted in phospholipid vesicles with the new G protein as well as with Gi or Go. The proportion of the high affinity sites increased with the concentrations of the G proteins, the potency of the new G protein being similar to that of Gi but a little lower than that of Go. This GTP-sensitive high affinity binding was not observed when each G protein was pretreated with pertussis toxin and then reconstituted with muscarinic receptors. Acetylcholine accelerated the dissociation of [3H]GDP from the new G protein as well as from Gi and Go, which were reconstituted with muscarinic receptors. These results indicate that muscarinic receptors interact with at least the above three kinds of G proteins, in a pertussis toxin-sensitive manner.
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PMID:Cerebral muscarinic acetylcholine receptors interact with three kinds of GTP-binding proteins in a reconstitution system of purified components. 249 27

The role of G proteins in cholinergic suppression of Ca2+-activated K current was studied in isolated canine colonic myocytes with the whole cell voltage-clamp technique. Acetylcholine (ACh; 10.0 microM) caused a 64 +/- 2.4% depression in the Ca2+-dependent component of the outward current evoked at potentials between -45 and -15 mV when GTP (0.1 microM) was included in the pipette-filling solution. This effect was reversed within 2-4 min on washout of ACh. Without GTP in the filling solution, ACh caused a 15 +/- 2.5% depression in outward current in 60% of the cells tested. When the non-hydrolyzable GTP analogues, GTP gamma S (0.1 mM) or 5'-guanylylimidodiphosphate (GppNHp; 0.1 mM) were used, the decrease in outward current was greater (85 +/- 4.2 and 78 +/- 6.5%, respectively), and it was not reversed on withdrawal of ACh. Dialysis of the cell interior with pipette solution containing pertussis toxin (1 ng/ml) for 30 min had no effect on the whole cell currents evoked on depolarization, but it abolished the effect of ACh on Ca2+-dependent outward current. These data suggest that coupling of muscarinic receptors to the inhibition of Ca2+-activated K channels is mediated by pertussis toxin-sensitive G proteins in colonic smooth muscle cells. G protein-mediated inhibition is distinctly different from the opening of muscarinic-regulated K channels in other cell types.
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PMID:G proteins mediate suppression of Ca2+-activated K current by acetylcholine in smooth muscle cells. 250 60


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