Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Elementary Na+ currents were recorded at 19 degrees C in cell attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the effect of cAMP and other 6-aminopurines. The treatment of the cardiocytes with db-cAMP (1 x 10(-3) mol/liter) led to a decline of reconstructed macroscopic peak INa to 62 +/- 7.6% of the initial control value. This reduction in NPo was mostly accompanied by a decrease in burst activity. Open-state kinetics were preserved even in DPI-modified, noninactivating Na+ channels. Since the stimulator of the adenylate cyclase, forskolin (1 x 10(-6) mol/liter), evoked a similar pattern of response, the NPo decrease can be considered as the functional correlate of Na+ channel phosphorylation brought about by cAMP-dependent protein kinase. As found in inside-out patches, cAMP (1 x 10(-3) mol/liter) remained effective under cell-free conditions and reduced reconstructed macroscopic peak INa to about 50% of the initial control value when the absence of Mg-ATP at the cytoplasmic membrane surface prevents phosphorylation reactions. A very similar response developed in the cytoplasmic presence of other 6-aminopurines including ATP (1 x 10(3) mol/liter), adenosine (1 x 10(-4) mol/liter), adenine (1 x 10(-5) mol/liter) and hypoxanthine (1 x 10(-5) mol/liter). This susceptibility to adenine suggests that cardiac Na+ channels in situ could sense intracellular fluctuations of adenine nucleotides, most likely of ATP.
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PMID:Na+ channel blockade by cyclic AMP and other 6-aminopurines in neonatal rat heart. 164 34

The effect of forskolin on voltage-activated Na+ and K+ currents in nodes of Ranvier from the toad, Bufo marinus, has been examined using the vaseline-gap voltage-clamp technique. Peak Na+ currents (INa) were reduced by 35% and the rate of decline of Na+ current during continuous depolarization was accelerated following treatment with 450 microM forskolin. However, the voltage-dependence of steady-state inactivation as well as the rate of recovery from fast inactivation remained unchanged. Upon repetitive depolarization at 1-10 Hz, a further inhibition of INa (approximately 60%) was observed. This use-dependent or phasic inhibition recovers slowly at -80 mV (tau approximately 13 s) and had a voltage-dependence like that of activation of the Na conductance. Near maximal steady-state phasic inhibition occurred with depolarizing pulse durations of only 4 ms, consistent with a direct involvement of the open Na+ channel in the blocking process. Inhibition of the delayed K+ current (IK) was characterized by a concentration-dependent reduction in steady-state current amplitude (IC50 approximately 80 microM) and a concentration-independent acceleration of current inactivation. A similar inhibition of IK was obtained with 1,9-dideoxyforskolin, a homolog which does not activate adenylate cyclase (AC). The results suggest that the inhibition IK and perhaps INa follows directly from drug binding and is not a consequence of AC activation.
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PMID:Inhibition of voltage-dependent Na+ and K+ currents by forskolin in nodes of Ranvier. 256 Jan 69

We have measured by radioimmunoassay the amount of total, free, and bound forms of cyclic AMP (cAMP) within the abdominal ganglion and in five identified cell bodies of neurons from Aplysia californica. In the abdominal ganglion the unbound (free) cAMP levels comprised approximately 25-30% of the total cAMP content under the unstimulated condition, i.e., bathed in high-magnesium saline. Under pharmacological conditions that blocked endogenous phosphodiesterase and activated adenylate cyclase, ganglionic free cAMP levels were elevated more than fourfold, while bound cAMP levels more than doubled. Freeze-substitution techniques were employed to facilitate isolation of individual cell bodies either before or after pharmacological manipulation of cAMP levels. The basal, free cAMP content of cells R2, LP1, R15, L11, and L2-L6 was in the range of 10-40 pmol/mg of cell protein, which accounted for approximately one-half of the total cAMP content per cell body. Determinations of individual cell volumes indicated that the basal, free cAMP concentrations ranged from 1 to 6 microM. Under the same pharmacological conditions that elevated ganglionic cAMP in levels, no changes were measured in either the free or the bound forms of cAMP in isolated cell bodies. Our results indicate that the cAMP elevation was compartmentalized within the neuropilar region of the ganglion, most likely within the processes of the nerve cells. Previous results demonstrated that cAMP injections into the same Aplysia neurons studied here induced a cAMP-activated sodium current, INa (cAMP). In this report we discuss the possibility that pharmacological elevation of cAMP within neuronal processes may reach concentrations similar to those produced by cAMP injections into somata.
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PMID:Compartmentalization of cyclic AMP elevation in neurons of Aplysia californica. 303 61

We have recently shown that beta-adrenergic agonists enhance the cardiac sodium current (INa) in rabbits through dual G-protein regulatory pathways. To determine if muscarinic cholinergic receptor stimulation can also modulate INa, we studied the effects of acetylcholine (ACh) and carbachol on INa in enzymatically dispersed rabbit ventricular myocytes. Whole-cell patch-clamp experiments done at room temperature using 20 mM [Na+]o showed that 100 nM isoproterenol increased INa and accelerated current decay as previously described. ACh (1 microM) or carbachol (1 microM) significantly reversed the stimulatory isoproterenol effects at test potentials throughout the INa activation range and at holding potentials negative to -80 mV. This effect was completely inhibited by atropine (1 microM) and was confirmed by studying single-channel INa from cell-attached patches. When INa was stimulated by forskolin (1 microM), carbachol (1 microM) significantly reversed the effect. The muscarinic-mediated inhibition of INa was inhibited by pertussis toxin (0.1 or 1.0 microgram/ml) incubation (12-15 hours), suggesting that the effect was inhibitory G-protein dependent. Further investigation of the ACh inhibitory mechanism revealed that ACh alone had no effect on INa and that when cells were dialyzed with cAMP (5 microM), ACh failed to inhibit INa. Furthermore, cGMP failed to inhibit the effect of isoproterenol on INa. These data suggest that ACh acts at or proximal to adenylate cyclase stimulation. Thus, rabbit cardiac Na+ channels are regulated by muscarinic agonists in a fashion similar to cardiac Ca2+ channels.
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PMID:Acetylcholine reversal of isoproterenol-stimulated sodium currents in rabbit ventricular myocytes. 843 82

1. In current-clamp recordings, 1 microM prostaglandin E2 (PGE2) increased the excitability of neonatal rat dorsal root ganglion neurones. The current threshold for firing was reduced, and the response to a constant suprathreshold stimulation was modified such that a single evoked action potential was converted to a train of action potentials. The excitatory action of PGE2 was still apparent when action potentials were evoked in the presence of 500 nM tetrodotoxin. 2. In voltage-clamp experiments 1 microM PGE2 frequently increased the magnitude of the peak currents recorded, and caused a hyperpolarizing shift (of approximately 6 mV) in the activation curve for the tetrodotoxin-resistant sodium current (TTX-R INa). In some cells, the hyperpolarizing shift in the activation curve was accompanied by a decrease in peak conductance. PGE2 also caused a hyperpolarizing shift in the steady-state inactivation curve for the sodium current. 3. Extracellular application of the cAMP analogue dibutyryl cAMP (dbcAMP) at a concentration of 1 mM produced effects on both the current-voltage relationship and the steady-state inactivation curve for the TTX-R INa which were indistinguishable from those observed with PGE2. Prior exposure of the neurones to dbcAMP occluded the effect of a subsequent treatment with PGE2. 4. Forskolin (10 microM), a direct activator of adenylate cyclase, mimicked the effects of PGE2 and dbcAMP on TTX-R INa. The inactive congener of forskolin, 1, 9-dideoxyforskolin (10 microM), reduced the amplitude of TTX-R INa, but did not evoke a hyperpolarizing shift in the activation curve. 5. Intracellular perfusion of the neurones with an inhibitor of protein kinase A inhibited the effect of PGE2 on TTX-R INa. 6. PGE2 also reduced the amplitude of voltage-gated potassium currents (IK), which will contribute to the excitatory action. The mechanisms underlying the changes in IK have yet to be elucidated. 7. We propose that the PGE2-mediated increase in excitability in sensory neurones may be due, at least in part, to the cAMP-protein kinase A-dependent modulation of the tetrodotoxin-resistant sodium channel.
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PMID:PGE2 modulates the tetrodotoxin-resistant sodium current in neonatal rat dorsal root ganglion neurones via the cyclic AMP-protein kinase A cascade. 888 54

Essential polyunsatured fatty acids have been shown to modulate enzymes, channels and transporters, to interact with lipid bilayers and to affect metabolic pathways. We have previously shown that eicosapentanoic acid (EPA, C20:5, n-3) activates epithelial sodium channels (ENaCs) in a cAMP-dependent manner involving stimulation of cAMP-dependent protein kinase (PKA). In the present study, we explored further the mechanism of EPA stimulation of ENaC in A6 cells. Fluorescence resonance energy transfer experiments confirmed activation of PKA by EPA. Consistent with our previous studies, EPA had no further stimulatory effect on amiloride-sensitive transepithelial current (INa) in the presence of CPT-cAMP. Thus, we investigated the effect of EPA on cellular pathways which produce cAMP. EPA did not stimulate adenylate cyclase activity or total cellular cAMP accumulation. However, membrane-bound phosphodiesterase activity was inhibited by EPA from 2.46 pmol/mg of protein/min to 1.3 pmol/mg of protein/min. To investigate the potential role of an A-kinase-anchoring protein (AKAP), we used HT31, an inhibitor of the binding between PKA and AKAPs as well as cerulenin, an inhibitor of myristoylation and palmitoylation. Both agents prevented the stimulatory effect of EPA and CPT-cAMP on INa and drastically decreased the amount of PKA in the apical membrane. Colocalization experiments in A6 cells cotransfected with fluorescently labeled ENaC beta subunit and PKA regulatory subunit confirmed the close proximity of the two proteins and the membrane anchorage of PKA. Last, in A6 cells transfected with a dead mutant of Sgk, an enzyme which up-regulates ENaCs, EPA did not stimulate Na+ current. Our results suggest that stimulation of ENaCs by EPA occurs via SGK in membrane-bound compartments containing an AKAP, activated PKA, and a phosphodiesterase.
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PMID:Epithelial Na+ channel stimulation by n-3 fatty acids requires proximity to a membrane-bound A-kinase-anchoring protein complexed with protein kinase A and phosphodiesterase. 1747 24