Effect Of DBcGMP Research Articles

Activation of inwardly rectifying K+ channel in OK proximal tubule cells involves cGMP-dependent phosphorylation process.

The inwardly rectifying K+ channel with an inward conductance of about 90 pS in the surface membrane of cultured opossum kidney proximal tubule (OKP) cell is activated by cyclic AMP-dependent protein kinase (PKA). In this study, we further examined the involvement of the guanosine 3',5'-cyclic monophosphate (cGMP)-dependent process in modulation of this K+ channel by using the patch-clamp technique. In cell-attached patches, channel activity was increased by the application of either N2, 2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate (DBcGMP, 100 microM) or 8-bromoguanosine 3',5'-cyclic monophosphate (8BrcGMP, 100 microM), and it was inhibited by KT5823 (10 microM), a membrane-permeable specific inhibitor of cGMP-dependent protein kinase (PKG). The effect of DBcGMP on channel activity was abolished by the pretreatment of cells with KT5823 (10 microM), but it was observed in the presence of KT5720 (200 nM), a specific inhibitor of PKA. Furthermore, atrial natriuretic peptide (ANP, 10 nM) increased channel activity, which was also prevented by the application of KT5823 (10 microM). In inside-out patches, ATP (3 mM) was required to maintain channel activity, which was inhibited by KT5823 (10 microM), but it was not increased by cGMP (100 microM) alone. The channel activity was increased by the coapplication of PKG (500 U/ml) and cGMP (100 microM). These results suggest that cGMP activates the inwardly rectifying K+ channel in OKP cells through PKG-mediated phosphorylation processes independent of PKA-mediated processes, and that ANP is an agonist which stimulates PKG-mediated processes in the proximal tubule cell. Furthermore, it is suggested that the ATP-dependent channel activity in inside-out patches is maintained at least in part by PKG, which is the membrane-bound catalytic domain.

Influence of nitric oxide on transepithelial transport in toad skin: effects of cholinergic agents and morphine

The effects induced by l-arginine ( l-Arg) on the short-circuit current and potential difference of Pleurodema thaul skin were investigated. l-Arg, but not d-Arg significantly increased the short-circuit current and potential difference when applied to the serosal surface. The effects of l-Arg were antagonized by amiloride, N G-nitro-methyl- l-arginine ( l-NAME) and by methylene blue. Carbachol and acetylcholine induced significant increases of both electrical parameters of the toad skin. These effects of the muscarinic cholinergic drugs were potentiated by a low concentration of l-Arg and antagonized by l-NAME or methylene blue. Carbachol and acetylcholine induced significant increases of both electrical parameters of the toad skin. These effects of the muscarinic cholinergic drugs were potentiated by a low concentration of l-Arg and antagonized by l-NAME or methylene blue. Addition of dibutyryl cyclic guanosyl monophosphate (db cGMP) or dibutyryl cyclic adenosine monophosphate (db cAMP) increased short-circuit current and potential difference. The effects of db cGMP, but not those of db cAMP were antagonized by l-NAME. The consecutive application of db cGMP and db cAMP induced additive effects. These results suggest that l-Arg increases transport in toad skin presumably acting through the formation of nitric oxide, which then stimulates cytoplasmic guanylate cyclase and leads to increased Na + and K + transport. The effects of l-Arg and carbachol were antagonized by acute application of morphine; however, a rebound response was observed when carbachol or noradrenaline were given after prolonged exposure of the skin to morphine, which suggests an adaptive response of the skin involving both cGMP and cAMP. Responses to both nucleotides were unchanged by morphine.

Antidiuretic effects of dibutyryl-cyclic GMP by micro-injecting into the supraoptic and paraventricular nuclei in the rat hypothalamus

We have reported antidiuretic effects of various neurotransmitters, such as noradrenaline(NA) and acetylcholine(ACh), and cyclic AMP and dibutyryl-cyclic AMP(db-cAMP) on urine outflow by microinjecting into the vasopressinergic supraoptic(SON) and paraventricular(PVN) nuclei. In this study, the effects of cyclic GMP(cGMP) and dibutyryl-cyclic GMP(db-cGMP) were investigated. The microinjections of cGMP into PVN only and of db-cGMP into both nuclei elicited dose-dependent antidiuretic effects. The median effective doses(ED50) for db-cGMP injected into SON and PVN were approx. 150 and 200 nmol, respectively. The effect of db-cGMP in SON was more potent than that of cGMP and was approx. equal to that of db-cAMP, which was almost completely blocked by the pretreatment of atropine. The effect of db-cGMP in PVN was slightly more potent than that of cGMP and less potent than that of db-cAMP, which was almost perfectly blocked by both atropine and phenoxybenzamine. A repeated microinjection of db-cGMP into these nuclei reduced the effect markedly. These results suggest that cGMP may have a role as a second messenger in the release of ACh in both nuclei and in the release of NA in PVN.

Dibutyryl cyclic GMP, morphine and Met-enkephalin: Lack of common actions on neuronal firing

The effects of microiontophoretically administered dibutyryl cyclic GMP (dbcGMP), morphine and Met-enkephalin on neuronal firing in the mesencephalic reticular formation of the rat were examined. DbcGMP did not mimic the ability of either opioid to block neuronal firing evoked by a nociceptive stimulus. Furthermore, dbcGMP did not potentiate the ability of the opioid to block evoked neuronal firing. The only effect of dbcGMP was an occasional enhancement of both evoked and spontaneous neuronal firing. These data may indicate that the effects of morphine and Met-enkephalin in the mesencephalic reticular formation of the rat are not linked to cyclic GMP.

Rheological studies of the contractile force within platelet-fibrin clots: Effects of prostaglandin E 1, dibutyryl-cAMP and dibutyryl-cGMP

Platelet-fibrin contractile force and the rate and extent of platelet-fibrin clot relaxation were measured in a Weissenberg rheogoniometer following recalcification of platelet-rich plasma (PRP). Following recalcification of PRP, there was a rapid increase in platelet-fibrin contractile force. Maximum platelet-fibrin contractile force was reduced by 40–80% in recalcified normal PRP following 50 minute pre-incubation with DBcAMP (5×10 −4 and 4×10 −3M). In the presence of PGE 1 (1.4×10 −4M), maximum platelet-fibrin contractile force was reduced by 50% in recalcified factor VIII-deficient PRP (in which less thrombin is generated). Rapid relaxation of contracted platelet-fibrin clots occurred in the presence of either PGE 1 or DBcAMP. No effect of DBcGMP was detected on platelet-fibrin interaction, contraction or relaxation in the rheogoniometer. These data on dynamic platelet-fibrin viscoelastic properties indicate that compounds which increase platelet cAMP levels inhibit platelet contractility.

A promoting action of cyclic GMP on contractions of guinea-pig vas deferens

The effect of dbc-GMP has been studied in ductus deferens of the guinea-pig. The nucleotide potentiated the contractions induced by electrical field stimulation and by adrenergic agonists. The site of action was probably in the smooth muscle cell, since the release of excitatory transmittor was not influenced.

Effect of cyclic 3',5'-guanosine monophosphate on human platelet function.

The relation of cyclic 3',5'-guanosine monophosphate (cGMP) to platelet function was studied by investigating the influence of this compound and its N2,O2'-dibutyryl derivative (DBcGMP) on platelet aggregation and the release reaction. Both cGMP and dibutyryl cGMP enhanced to an equal extent platelet aggregation induced by epinephrine or by chick skin collagen alpha1 chain. The platelet release reaction, as measured by the release of [14C]-labeled 5-hydroxytryptamine (serotonin) was also enhanced by the cyclic nucleotides. Both compounds were also able to partially overcome the inhibitory effect of N6,O2'-dibutyryl 3',5'-adenosine monophosphate (DBcAMP), prostaglandin E1, and theophylline. The effect of DBcGMP did not result from contamination with 5'-GMP. Butyric acid and 5'-GMP, either alone or in combination, had no detectable effect on platelet function. The in vitro effect of DBcGMP and cGMP was not dependent on preincubation of platelets with the compounds. This suggests that their effect is mediated by direct action on the platelet membranes. These data are consistent with previous observations that the platelet aggregating agents (epinephrine, ADP, collagen, and chick collagen alpha1 chains) cause an increase in the content of GMP, and support the hypothesis that platelet aggregation is favored by an increase in cGMP.