Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.12 (PKG)
 2,515 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The slow inward Ca2+ current, ICa, is fundamental in the initiation of cardiac contraction and neurohormonal regulation of cardiac function. It is increased by beta-adrenergic agonists, which stimulate synthesis of cyclic AMP (cAMP) and cAMP-dependent phosphorylation. The neurotransmitter acetylcholine reduces ICa by an unknown mechanism. There is strong evidence that acetylcholine reduces ICa by decreasing adenylate cyclase activity, but cGMP has also been implicated as ACh stimulates cGMP accumulation and activates cGMP-dependent protein kinase. Application of cGMP decreases contractile force, decreases Ca flux, shortens the duration of action potentials and inhibits Ca-dependent action potentials. Other studies, however, have concluded that cGMP levels do not correlate with contractile force and that cGMP has no effect on ICa. We have therefore examined the effects of intracellular perfusion of cGMP on ICa using isolated, voltage-clamped cells from frog ventricle. We find that cGMP has negligible effects on basal ICa, but greatly decreases the ICa that had been elevated by beta-adrenergic agonists or by intracellular perfusion with cAMP. The decrease of ICa is mediated by cAMP hydrolysis via a cGMP-stimulated cyclic nucleotide phosphodiesterase.
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PMID:Opposite effects of cyclic GMP and cyclic AMP on Ca2+ current in single heart cells. 242 89

The effects of acetylcholine and sodium nitroprusside on the activity of cGMP-dependent protein kinase were studied in the perfused rat heart. Acetylcholine produced a dose-dependent increase in cGMP levels and cGMP-dependent protein kinase activity, and reduced the force of contraction. Both acetylcholine and sodium nitroprusside produced rapid increases in cardiac cGMP, with nitroprusside being the more potent agent. Only acetylcholine, however, raised the activity ratio of the cGMP-dependent protein kinase and decreased the force of contraction. Whereas acetylcholine and nitroprusside were slightly additive in their effects on total cGMP levels, the increase in the activity ratio of the cGMP-dependent protein kinase and the decrease in the force of contraction produced by acetylcholine were unchanged by nitroprusside. The results suggest that the cGMP produced by acetylcholine, but not nitroprusside, was coupled to protein kinase activation in this tissue.
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PMID:Effects of acetylcholine and nitroprusside on cGMP-dependent protein kinase in the perfused rat heart. 625 Nov 21

The signal transduction cascade between the activation of the somatostatin (SOM) receptor and modulation of transmitter release was study using Acetylcholine (Ach) release measurements and patch clamp recordings of Ca2+ current from acutely dissociated St 40 ciliary ganglion neurons. As in intact synapses, somal ACh release was blocked by 100 nM SOM or 100 microM dibutyril cGMP, and the SOM-mediated inhibition could be reversed by 10 microM 1-NAME (a selective inhibitor of nitric oxide synthase, NOS) or 100 microM Rp-8p-CPT-cGMPs (a selective inhibitor of a cGMP protein dependent kinase, PKG). In whole cell recordings, SOM inhibition of Ca2+ current rapidly relaxes to control levels but is sustained in perforated patch recordings which decreases cell dialysis. Inhibition of NOS or PKG in perforated patch recordings, however caused SOM effects to become transient again. We hypothesize that PKG alters the characteristics of the membrane-delimited G protein inhibition of Ca2+ current. Therefore SOM receptors trigger a membrane-delimited signal transduction cascade that is modulated by soluble messengers, converging on voltage activated Ca2+ channels. When both pathways are active together, SOM causes a sustained inhibition of neuronal Ca2+ current leading to a decrease in transmitter release.
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PMID:Membrane delimited and intracellular soluble pathways in the somatostatin modulation of ACh release. 863 27

Nitric oxide (NO.) is believed to mediate nitrovasodilators and acetylcholine-induced vasodilatation via increasing intracellular guanosine 3',5'-cyclic monophosphate (cGMP) levels. The cellular mechanisms involved in No.-mediated pulmonary vasodilatation are complex and include membrane hyperpolarization. Using the patch-clamp technique in cell-attached and inside-out configurations, we examined the effect of NO. gas, 3-morpholinosydnomimine hydrochloride (SIN-1), and perfusate from ACh-stimulated human pulmonary arterial endothelial cells, or endothelium-derived relaxing factors (EDRF), on the Ca(2+)-dependent K+ (KCa) channels in isolated cultured human pulmonary arterial smooth muscle cells (HPSMC). NO., SIN-1, and EDRF caused similar increases in KCa channel activity. Inhibiting cGMP generation with methylene blue or inhibiting the effect(s) of cGMP with the cGMP antagonist 8-bromoguanosine 3',5'-cyclic monophosphorothioate Rp isomer Rp-cGMPS prevented the NO.- and SIN-1-mediated activation of KCa channels, respectively. Treating the human pulmonary arterial endothelial cells with methylene blue blocked the EDRF-mediated activation of KCa channels in HPSMC. The cGMP analogue 8-bromo-cGMP increased KCa channel activity in intact cells and in excised inside-out HPSMC membrane patches. In the presence of cGMP and ATP, the alpha-isozyme of the cGMP-dependent protein kinase (I alpha-cGMP-PK) significantly increased KCa channel activity, and the channel activation was further increased on addition of the protein phosphatase inhibitors okadaic acid and calyculin A. Furthermore, the cGMP-mediated KCa channel activation was reduced by the cyclic nucleotide-dependent protein kinase inhibitor N-[2-methylamino)ethyl]-5-isoquinlinesulfonamide (H-8). Thus, in HPSMC, the mechanism of NO.- and native EDRF-induced KCa channel activation appears to be mediated via cGMP-I alpha-cGMP-PK phosphorylation of KCa channels.
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PMID:Regulation of Ca(2+)-activated K+ channels in pulmonary vascular smooth muscle cells: role of nitric oxide. 888 62

The effects of bath-applied sodium nitroprusside (SNP), a nitric oxide (NO) donor, on an acetylcholine ACh-induced K+ current recorded from identified neurons (R9 and R10) of Aplysia kurodai were investigated with conventional voltage-clamp and pressure ejection techniques. Bath-applied SNP (25-50 microM) reduced the ACh-induced K+ current in the neurons without affecting the resting membrane conductance and holding current. The suppressing effects of SNP on the current were completely reversible. Intracellular injection of 1 mM guanosine 3',5'-cyclic monophosphate (cGMP) or bath-applied 50 microM 3-isobutyl-1-methylxanthine (IBMX), a nonspecific phosphodiesterase (PDE) inhibitor, also inhibited the ACh-induced current, thus mimicking the effect of the NO donor on the ACh-induced current. In contrast, pretreatment with methylene blue (10 microM), an inhibitor of guanylate cyclase, and hemoglobin (50 microM), a nitric oxide scavenger, decreased the SNP-induced inhibition of the ACh-induced current. These results suggest that SNP, a NO donor, inhibits the ACh-induced K+ current, and that the mechanism of NO inhibition of the ACh-induced current recorded from identified Aplysia neurons involves cGMP-dependent protein kinase.
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PMID:Nitric oxide donor sodium nitroprusside inhibits the acetylcholine-induced K+ current in identified Aplysia neurons. 892 26

Acetylcholine has long been implicated in nocturnal phase adjustment of circadian rhythms, yet the subject remains controversial. Although the suprachiasmatic nucleus (SCN), site of the circadian clock, contains no intrinsic cholinergic somata, it receives choline acetyltransferase-immunopositive projections from basal forebrain and mesopontine tegmental nuclei that contribute to sleep and wakefulness. We have demonstrated that the SCN of inbred rats in a hypothalamic brain slice is sensitive to cholinergic phase adjustment via muscarinic receptors (mAChRs) only at night. We used this paradigm to probe the muscarinic signal transduction mechanism and the site(s) gating nocturnal responsiveness. The cholinergic agonist carbachol altered the circadian rhythm of SCN neuronal activity in a pattern closely resembling that for analogs of cGMP; nocturnal gating of clock sensitivity of each is preserved in vitro. Specific inhibitors of guanylyl cyclase (GC) and cGMP-dependent protein kinase (PKG), key elements in the cGMP signal transduction cascade, blocked phase shifts induced by carbachol. Further, carbachol administration to the SCN at night increased cGMP production and PKG activity. The carbachol-induced increase in cGMP was blocked both by atropine, an mAChR antagonist, and by LY83583, a GC inhibitor. We conclude that (1) mAChR regulation of the SCN is mediated via GC-->cGMP-->PKG, (2) nocturnal gating of this pathway is controlled by the circadian clock, and (3) a gating site is positioned downstream from cGMP. This study is among the first to identify a functional context for mAChR-cGMP coupling in the CNS.
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PMID:Coupling of muscarinic cholinergic receptors and cGMP in nocturnal regulation of the suprachiasmatic circadian clock. 898 88

We have examined the somatostatin-mediated modulation of acetylcholine release from intact chick embryo choroid tissue and compared these data with those obtained using acutely dissociated neuronal cell bodies from the chick ciliary ganglion. Acetylcholine release, evoked in a calcium-dependent manner by a high potassium (55 mM KCI) stimulation in both preparations, was inhibited almost completely by 100 nM somatostatin. Measurement of intracellular calcium in these neurons revealed that somatostatin blocked the large calcium transient that was observed in control neurons following KCI exposure. The modulatory effect of somatostatin on transmitter release was significantly attenuated by pre-treatment with pharmacologic agents that selectively block cyclic GMP (cGMP)-dependent protein kinase (PKG) or nitric oxide (NO) synthase. It is interesting that this prevention of somatostatin-mediated acetylcholine release inhibition occurred without reversal of the somatostatin-mediated block of the KCl-evoked calcium transient. Furthermore, a NO donor or cGMP analogue could block KCI-evoked acetylcholine release, but only cGMP could reduce the KCI-evoked calcium transient. Although cGMP could reduce the KCI-evoked calcium transient, a cGMP analogue was shown to reduce calcium ionophore-evoked transmitter release. Thus, somatostatin reduces acetylcholine release by modulating calcium influx, but the NO-PKG pathway can inhibit acetylcholine release, and alter somatostatin-mediated inhibition, by affecting transmitter release at some point after calcium entry.
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PMID:A nitric oxide/cyclic GMP-dependent protein kinase pathway alters transmitter release and inhibition by somatostatin at a site downstream of calcium entry. 1021 75

We investigated the effect of carbachol (CCh) on L-type Ca2+ current (ICa(L)) enhanced by dialyzed adenosine 3',5'-cyclic monophosphate (cAMP) and/or bath-applied 3-isobutyl-1-methylxanthine (IBMX) in guinea pig isolated ventricular myocytes. At pipette concentrations ([cAMP]pip) from 30 microM to 1 mM, cAMP increased ICa(L) to 25.8 +/- 0.9 microA/cm2 (682 +/- 24.8% increase above control). CCh (100 microM) did not inhibit ICa(L) at any [cAMP]pip. IBMX, a nonselective phosphodiesterase (PDE) inhibitor, increased ICa(L) maximally at 300 microM IBMX (17.9 +/- 0.7 microA/cm2; 449 +/- 20% increase). CCh (100 microM) inhibited ICa(L) by 92 +/- 9.5% at 30 microM IBMX and 78 +/- 4.6% at 100 microM IBMX; this effect was reduced or absent at higher IBMX concentrations (300 and 1,000 microM). Coadministration of cAMP and IBMX also progressively suppressed inhibition by CCh. CCh had a negligible effect on ICa(L) at 750 microM IBMX in the absence of pipette cAMP and at 50 microM IBMX in the presence of 100 microM [cAMP]pip. ACh-activated K+ current (IK(ACh)) was unchanged in atrial myocytes dialyzed with 100 microM cAMP; this excludes a phosphorylation-dependent desensitization of the muscarinic receptor (mAChR) or Gi by cAMP. LY83583 (100 microM), an inhibitor of cyclic guanosine monophosphate (cGMP) production, attenuated inhibition of ICa(L) by CCh in the presence of IBMX. 8-Bromo-cGMP (8-Br-cGMP), an activator of cGMP-dependent protein kinase (PKG), mimicked CCh in its actions on ICa(L) raised by both cAMP (no significant change) and IBMX (49 +/- 5.1% inhibition). Okadaic acid, an inhibitor of type 1 and 2A phosphatases, blocked inhibition of IBMX-stimulated ICa(L) by either CCh or 8-Br-cGMP. Thus the ability of CCh to inhibit ICa(L) appears caused by cGMP/PKG activation of an okadaic acid-sensitive protein phosphatase, and elevated levels of cAMP protect against this action.
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PMID:Elevated cAMP suppresses muscarinic inhibition of L-type calcium current in guinea pig ventricular myocytes. 1044 83

The effects of N(G)-monomethyl-L-arginine (L-NMMA), a nitric-oxide synthase (NOS) inhibitor, on the L-type Ca(2+) current (ICa) and NO effects on NOS were determined in rat ventricular myocytes. L-NMMA (10 and 100 microM) had no significant effect on basal ICa, but in a cAMP-stimulated condition due to forskolin (1 microM) or milrinone (10 microM), a cGMP-inhibited cAMP-phosphodiesterase (PDE), L-NMMA (10 and 100 microM) concentration dependently augmented ICa. The enhancing effects of L-NMMA (10 and 100 microM) on ICa were not seen in the presence of either a nonselective inhibitor of PDE, 3-isobutyl-1-methylxanthine (20 microM), resulting in a stimulated ICa condition or a cGMP-dependent protein kinase activator, 8-bromo-cGMP (200 microM). 8-Bromo-cGMP (200 microM) inhibited 100 microM L-NMMA-induced ICa increase in the simultaneous application of forskolin (1 microM). Acetylcholine (ACh; 1 and 3 microM) inhibited 1 microM forskolin-stimulated ICa in a concentration-dependent manner, but this inhibitory action of ACh was significantly attenuated by the additional application of L-NMMA (100 microM). In the continuing presence of both L-NMMA (100 microM) and forskolin (1 microM), ACh (6 microM) had no inhibitory effect on ICa. In another series of experiments with isolated ventricular myocytes, we obtained both the positive staining of NADPH-diaphorase activity and the expression of the endothelial isoform of NOS. These data suggest that the effect of L-NMMA on ICa in a cAMP-stimulated condition with or without cholinergic inhibition is due to inhibition (acute effects) of a cGMP-stimulated cAMP-PDE via inhibition of the endothelial isoform of NOS.
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PMID:Effects of N(G)-monomethyl-L-arginine on Ca(2+) current and nitric-oxide synthase in rat ventricular myocytes. 1087 15

Glutamate is a major fast excitatory neurotransmitter in the CNS including the hypothalamus. Our previous experiments in hypothalamic neuronal cultures showed that a long-term decrease in glutamate excitation upregulates ACh excitatory transmission. Data suggested that in the absence of glutamate activity in the hypothalamus in vitro, ACh becomes the major excitatory neurotransmitter and supports the excitation/inhibition balance. Here, using neuronal cultures, fura-2 Ca(2+) digital imaging, and immunocytochemistry, we studied the mechanisms of regulation of cholinergic properties in hypothalamic neurons. No ACh-dependent activity and a low number (0.5%) of cholinergic neurons were detected in control hypothalamic cultures. A chronic (2 wk) inactivation of N-methyl-D-aspartate (NMDA) ionotropic glutamate receptors, L-type voltage-gated Ca(2+) channels, calmodulin, Ca(2+)/calmodulin-dependent protein kinases II/IV (CaMK II/IV), or protein kinase C (PKC) increased the number of cholinergic neurons (to 15-24%) and induced ACh activity (in 40-60% of cells). Additionally, ACh activity and an increased number of cholinergic neurons were detected in hypothalamic cultures 2 wk after a short-term (30 min) pretreatment with bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid tetrakis(acetoxy-methyl) ester (BAPTA AM; 2.5 microM), a membrane permeable Ca(2+)-chelating agent that blocks cytoplasmic Ca(2+) fluctuations. An increase in the number of cholinergic neurons following a chronic NMDA receptor blockade was likely due to the induction of cholinergic phenotypic properties in postmitotic noncholinergic neurons, as determined using 5-bromo-2'-deoxyuridine (BrdU) labeling. In contrast, a chronic inactivation of non-NMDA glutamate receptors or cGMP-dependent protein kinase had little effect on the expression of ACh properties. The data suggest that Ca(2+), at normal intracellular concentrations, tonically suppresses the development of cholinergic properties in hypothalamic neurons. However, a decrease in Ca(2+) influx into cells (through NMDA receptors or L-type Ca(2+) channels), inactivation of intracellular Ca(2+) fluctuations, or downregulation of Ca(2+)-dependent signal transduction pathways (CaMK II/IV and PKC) remove the tonic inhibition and trigger the development of cholinergic phenotype in some hypothalamic neurons. An increase in excitatory ACh transmission may represent a novel form of neuronal plasticity that regulates the activity and excitability of neurons during a decrease in glutamate excitation. This type of plasticity has apparent region-specific character and is not expressed in the cortex in vitro; neither increase in ACh activity nor change in the number of cholinergic neurons were detected in cortical cultures under all experimental conditions.
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PMID:Calcium-dependent regulation of cholinergic cell phenotype in the hypothalamus in vitro. 1220 56


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