Mechanism of action of γ-aminobutyric acid on frog melanotrophs

1995 ◽  
Vol 14 (1) ◽  
pp. 1-12 ◽  
Author(s):  
L Desrues ◽  
H Vaudry ◽  
M Lamacz ◽  
M C Tonon
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Inhibitory Effect ◽  
Aminobutyric Acid ◽  
Calcium Stores ◽  
Camp Production ◽  
Biphasic Effect ◽  
Camp Levels ◽  
Camp Formation ◽  
Stimulation Of

ABSTRACT We have previously demonstrated that γ-aminobutyric acid (GABA) is a potent regulator of secretory and electrical activity in melanotrophs of the frog pituitary. The aim of the present study was to investigate the intracellular events which mediate the response of melanotrophs to GABA. We first observed that GABA (1–100 μm inhibited both basal and forskolin-stimulated cyclic AMP (cAMP) formation. The inhibitory effect of GABA on cAMP levels was mimicked by the GABAB receptor agonist baclofen (100 μm) and totally abolished by a 4-h pretreatment with pertussis toxin (01 μg/ml). In contrast, the specific GABAA agonist 3-aminopropane sulphonic acid (3APS) did not affect cAMP production. Both GABA and 3APS (100 μm each) induced a biphasic effect on α-MSH release from perifused frog neurointermediate lobes, i.e. a transient stimulation followed by an inhibition of α-MSH secretion. Administration of forskolin (10 μm) prolonged the stimulatory phase and attenuated the inhibitory phase evoked by GABA and 3APS, indicating that cAMP modulates the response of melanotrophs to GABAA agonists. Ejection of 3APS (1 μm) in the vicinity of cultured melanotrophs caused a massive increase in intracellular calcium concentration ([Ca2+]i). The stimulatory effect of 3APS on [Ca2+]i was abolished when the cells were incubated in a chloride-free medium. The formation of inositol trisphosphate was not affected by 3APS, suggesting that the increase in [Ca2+]i cannot be ascribed to mobilization of intracellular calcium stores. ω-Conotoxin did not alter the secretory response of frog neurointermediate lobes to 3APS, while nifedipine blocked the stimulation of α-MSH secretion induced by 3APS. In conclusion, the present data indicate that, in frog pituitary melanotrophs, (i) the stimulatory phase evoked by GABAA agonists can be accounted for by an influx of calcium through L-type calcium channels, (ii) the inhibitory effect evoked by GABAB agonists can be ascribed to inhibition of adenylate cyclase activity and (iii) cAMP attenuates the inhibitory phase evoked by GABAA agonists. Taken together, these data suggest that activation of GABAB receptors may modulate GABAA receptor function.

Prostaglandin E2-histamine in interactions on cAMP, cGMP, and acid production in isolated fundic glands

1982 ◽  
Vol 242 (1) ◽  
pp. G21-G26 ◽  
Author(s):  
R. A. Levine ◽  
K. R. Kohen ◽  
E. H. Schwartzel ◽  
C. E. Ramsay
Keyword(s):  
Prostaglandin E2 ◽  
Acid Secretion ◽  
Acid Production ◽  
Camp Production ◽  
Histamine Stimulation ◽  
Fundic Mucosa ◽  
Biochemical Responses ◽  
Camp Levels ◽  
Camp And Cgmp ◽  
Stimulation Of

Relations among cAMP, cGMP, acid production [measured by the intraglandular accumulation of [14C]aminopyrine (AP)], and prostaglandin E2 (PGE2) activity were studied in isolated glands from rabbit fundic mucosa. AP, cAMP, and cGMP responses to histamine, PGE2, and 3-isobutyl-1-methylxanthine (IMX) were compared with controls. Histamine and PGE2 significantly increased glandular cAMP levels twofold, and histamine and IMX stimulated AP uptake two- to fourfold. PGE2 significantly inhibited both histamine- and IMX-stimulated AP accumulation, but it did not alter basal AP uptake. PGE2 also decreased histamine-stimulated cAMP production but only at a low concentration (10(-7) M). This dose of PGE2 was near to the endogenous PGE2 content found in unstimulated glands (10(-8) M). Intraglandular cGMP levels in unstimulated glands (10(-8) M). Intraglandular cGMP levels were increased by IMX but not by PGE2 or histamine. It is concluded that histamine stimulation of acid secretion is mediated by cAMP, that secretory and biochemical responses to histamine are modulated by PGE2 because PGE2 antagonized histamine-stimulated cAMP and AP uptake, and that the rise in cAMP induced solely by PGE2 appears to be localized within nonparietal cells because PGE2 alone did not stimulate AP accumulation.

Changes In Triphosphatidylinositol Metabolism During PGE1- Induced Shape Change Of Washed Rabbit Platelets

1981 ◽  
Author(s):  
J D Vickers ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Phosphatidic Acid ◽  
Shape Change ◽  
Specific Radioactivity ◽  
Inositol Phospholipids ◽  
Rabbit Platelets ◽  
Turn Over ◽  
Camp Levels ◽  
Camp Formation ◽  
Platelet Shape ◽  
Stimulation Of

Since the inositol phospholipids are present in small amounts in platelets and turn over rapidly during platelet shape change, aggregation and release, they are thought to have a functional rather than structural role in platelets. We have previously reported that within 10 sec of stimulation of prelabeled, washed rabbit platelets with ADP, the amount of triphosphatidylinositol (TPI) is significantly reduced while the specific radioactivity of its [32p]phosphate is increased. One explanation of this result is that ADP- stimulation may divert ATP required for phosphorylation of diphosphatidylinositol (DPI) to TPI, leading to a decrease in the amount of TPI. PGE1 (10 μM) causes conversion of ATP to cAMP and induces a transient platelet shape change. The shape change may be due to the reduction in ATP with a concomitant fall in TPI. We have therefore studied whether PGE1-stimulation of washed rabbit platelets prelabeled with [32P] causes a change in TPI. Within 10 sec the amount of TPI in PGE1-treated platelets was reduced from 2.22 nmoles/ 109 platelets to 1.98 nmoles/109 platelets (p<0.05) although neither the [32P] labeling (51.1 × 103 dpm/109 platelets) nor specific radioactivity (24.1 × 103 dpm/nmole) were significantly changed. These results are compatible with the theory that diversion of ATP by PGE1-stimulation of cAMP formation from ATP, may reduce the amount of TPI. A similar effect was observed previously with ADP-stimulation. PGE1 caused no change in the [32p] labeling of phosphatidic acid (PA) (ADP caused a 290% increase) and caused only a small increase in its specific radioactivity (16% compared to 270% with ADP). If the rates of turnover of TPI and PA which are reflected in their specific radioactivities are Ca2+- dependent, Ca2+ sequestration due to increased cAMP levels induced by PGE1 would, after the initial effects, terminate these changes. The results further support the suggestion that reduction in the amount of TPI may be involved in platelet shape change and initiation of aggregation.

Increased prostacyclin and PGE2 stimulated cAMP production by macrophages from endotoxin-tolerant rats

1998 ◽  
Vol 274 (5) ◽  
pp. C1238-C1244 ◽  
Author(s):  
Michel A. Makhlouf ◽  
Lawrence P. Fernando ◽  
Thomas W. Gettys ◽  
Perry V. Halushka ◽  
James A. Cook
Keyword(s):  
Inflammatory Mediator ◽  
Phosphodiesterase Inhibitors ◽  
Mrna Levels ◽  
Cytokine Release ◽  
Camp Production ◽  
Receptor Mrna ◽  
Ep4 Receptor ◽  
Ip Receptor ◽  
Camp Levels ◽  
Camp Formation

Sublethal administration of lipopolysaccharide (LPS) renders rats tolerant to multiple lethal stimuli. Tolerant macrophages exhibit differential alterations in LPS-stimulated cytokine and inflammatory mediator release. Increased cAMP levels stimulated by PGE2 or prostacyclin (PGI2) result in differential effects on LPS-induced cytokine release and protect against the pathophysiological changes of endotoxemia. In the present studies, we sought to determine whether PGE2- and PGI2-stimulated cAMP levels are altered in tolerant macrophages. Incubation of macrophages with cicaprost or 11-deoxy-PGE1 in the presence of phosphodiesterase inhibitors resulted in significantly higher (2.5- to 6.5-fold) cAMP concentrations in tolerant macrophages compared with control. In contrast, isoproterenol-stimulated cAMP levels were not significantly different between control and tolerant cells. Also, incubation of tolerant macrophages with LPS did not result in significantly elevated cAMP levels. Prostacyclin (IP) receptor mRNA levels were significantly increased in tolerant cells compared with controls, whereas [3H]PGE2binding and PGE2 EP4 receptor mRNA levels were not significantly changed. These studies suggest that LPS tolerance induces selective alterations in eicosanoid regulation of cAMP formation.

scholarly journals Alteration of Platelet Cyclic AMP (cAMP) by Ethanol

1977 ◽  
Author(s):  
D.H. Cowan ◽  
M. Kikta ◽  
D. Baunach
Keyword(s):  
Cyclic Amp ◽  
Platelet Function ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Platelet Dysfunction ◽  
Camp Metabolism ◽  
Subnormal Level ◽  
Camp Levels ◽  
Stimulation Of

Studies of cAMP in human platelets exposed to ethanol were done to assess one possible mechanism for ethanol-related platelet dysfunction. Ingestion of ethanol by 3 subjects produced blood ethanol levels from 65-76 mM. Thrombocytopenia occurred in 1 subject and impaired platelet function occurred in all. Platelet cAMP decreased 36,51, and 59% below control levels. Infusion of ethanol to 2 normals produced blood ethanol levels of 43 mM and decreased platelet cAMP by 15% and 22%. Incubation of normal platelets with 86 mM ethanol in vitro decreased cAMP from 13.8 ± 2.9 (1 SD) to 9.4 ± 3.5 (p<0.02). By contrast, ethanol did not impair the increase in cAMP that occurred with 1.3 μM PGE1. Further, ethanol enhanced the increase in cAMP produced by 2.0 mM papaverine (Pap) by 160-220% and that produced by Pap + PGE1 by 58%. Dopamine, 0.1 mM, caused a 23% decrease in the basal level of cAMP, a 31% decrease below the subnormal level of cAMP seen with ethanol alone, and a 41% reduction in the increased level of cAMP produced by Pap + ethanol. The effect of ethanol on platelet cAMP metabolism is complex. Ethanol reduces basal levels of cAMP, does not decrease elevated levels that result from PGE1 stimulation of adenylate cyclase, and augments the inhibitory effect of Pap on platelet phosphodiesterase (PDE). Despite causing a decrease in basal cAMP levels, ethanol may impair platelet function by potentiating the effect of agents or other conditions which increase cAMP. The effect of ethanol on Pap-stimulated PDE activity may be blocked by dopamine, a neuropharmacologic agent that is actively accumulated by platelets.

scholarly journals Inhibitory Effect of Somatostatin-14 on L-Type Voltage-Gated Calcium Channels in Cultured Cone Photoreceptors Requires Intracellular Calcium

2009 ◽  
Vol 102 (3) ◽  
pp. 1801-1810 ◽  
Author(s):  
Kuihuan Jian ◽  
Rola Barhoumi ◽  
Michael L. Ko ◽  
Gladys Y.-P. Ko
Keyword(s):  
Calcium Channels ◽  
Intracellular Calcium ◽  
G Protein ◽  
Inhibitory Effect ◽  
Calcium Stores ◽  
Dependent Effect ◽  
Voltage Gated ◽  
Circadian Phase ◽  
Voltage Gated Calcium Channels ◽  
Somatostatin 14

The inhibitory effects of somatostatin have been well documented for many physiological processes. The action of somatostatin is through G-protein-coupled receptor-mediated second-messenger signaling, which in turn affects other downstream targets including ion channels. In the retina, somatostatin is released from a specific class of amacrine cells. Here we report that there was a circadian phase-dependent effect of somatostatin-14 (SS14) on the L-type voltage-gated calcium channels (L-VGCCs) in cultured chicken cone photoreceptors, and our study reveals that this process is dependent on intracellular calcium stores. Application of 500 nM SS14 for 2 h caused a decrease in L-VGCC currents only during the subjective night but not the subjective day. We then explored the cellular mechanisms underlying the circadian phase-dependent effect of SS14. The inhibitory effect of SS14 on L-VGCCs was mediated through the pertussis-toxin-sensitive G-protein-dependent somatostatin receptor 2 (sst2). Activation of sst2 by SS14 further activated downstream signaling involving phospholipase C and intracellular calcium stores. Mobilization of intracellular Ca2+ was required for somatostatin induced inhibition of photoreceptor L-VGCCs, suggesting that somatostatin plays an important role in the modulation of photoreceptor physiology.

Regulation of PI hydrolysis and cAMP formation by muscarinic M3 receptor in guinea pig gallbladder

1994 ◽  
Vol 267 (4) ◽  
pp. G523-G528
Author(s):  
T. Takahashi ◽  
S. Kurosawa ◽  
C. Owyang
Keyword(s):  
Guinea Pig ◽  
Inhibitory Effect ◽  
Dependent Manner ◽  
Biochemical Responses ◽  
Muscarinic Receptor Antagonists ◽  
M3 Receptor ◽  
Pi Hydrolysis ◽  
Dose Dependent ◽  
Camp Formation ◽  
Stimulation Of

Carbachol (10(-8)-10(-3) M) produced two distinct biochemical responses in the guinea pig gallbladder smooth muscle: simulation of phosphoinositide (PI) hydrolysis and inhibition of forskolin-mediated adenosine 3',5'-cyclic monophosphate (cAMP) formation in a dose-dependent manner. The mean effective dose (ED50) concentration (1.6 x 10(-5) M) of carbachol-mediated stimulation of PI hydrolysis was 145 times greater than the ED50 concentration (1.1 x 10(-7) M) of carbachol mediated inhibition of cAMP formation. The inhibitory effect of carbachol on cAMP formation was antagonized by the pretreatment of pertussis toxin. To determine whether these two biochemical responses were mediated by the same or different subtypes of muscarinic receptors, the relative potencies of muscarinic receptor antagonists were calculated by Schild analysis. The M3 muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) exhibited inhibitory constant (Ki) values at 0.3 and 1.2 nM in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. The corresponding Ki values for pirenzepine, a muscarinic M1 antagonist, were 11 and 130 nM. The corresponding Ki values for AF-DX 116, a muscarinic M2 antagonist, were 34 and 450 nM. Thus 4-DAMP was 37x and 108x more potent than pirenzepine in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. In addition, compared with AF-DX 116, 4-DAMP was 113x and 375x more potent in reducing stimulation of PI hydrolysis and inhibition of cAMP formation. Cholecystokinin (CCK) octapeptide (10(-10)-(10-6) M) caused a significant increase of PI hydrolysis but had no inhibitory effects on cAMP formation evoked by forskolin (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Elucidation of a TRPC6-TRPC5 Channel Cascade That Restricts Endothelial Cell Movement

2008 ◽  
Vol 19 (8) ◽  
pp. 3203-3211 ◽  
Author(s):  
Pinaki Chaudhuri ◽  
Scott M. Colles ◽  
Manjunatha Bhat ◽  
David R. Van Wagoner ◽  
Lutz Birnbaumer ◽  
...  
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Transient Receptor Potential ◽  
Calcium Influx ◽  
Cell Movement ◽  
Receptor Potential ◽  
Receptor Activation ◽  
Calcium Stores ◽  
Trpc Channels ◽  
Transient Receptor

Canonical transient receptor potential (TRPC) channels are opened by classical signal transduction events initiated by receptor activation or depletion of intracellular calcium stores. Here, we report a novel mechanism for opening TRPC channels in which TRPC6 activation initiates a cascade resulting in TRPC5 translocation. When endothelial cells (ECs) are incubated in lysophosphatidylcholine (lysoPC), rapid translocation of TRPC6 initiates calcium influx that results in externalization of TRPC5. Activation of this TRPC6–5 cascade causes a prolonged increase in intracellular calcium concentration ([Ca2+]i) that inhibits EC movement. When TRPC5 is down-regulated with siRNA, the lysoPC-induced rise in [Ca2+]i is shortened and the inhibition of EC migration is lessened. When TRPC6 is down-regulated or EC from TRPC6−/− mice are studied, lysoPC has minimal effect on [Ca2+]i and EC migration. In addition, TRPC5 is not externalized in response to lysoPC, supporting the dependence of TRPC5 translocation on the opening of TRPC6 channels. Activation of this novel TRPC channel cascade by lysoPC, resulting in the inhibition of EC migration, could adversely impact on EC healing in atherosclerotic arteries where lysoPC is abundant.

Forskolin perturbs cGMP as well as cAMP levels in human thyroid cells

1984 ◽  
Vol 107 (2) ◽  
pp. 225-229 ◽  
Author(s):  
Maria Luisa Brandi ◽  
Carlo M. Rotella ◽  
Andrea Lopponi ◽  
Leonard D. Kohn ◽  
Salvatore M. Aloj ◽  
...  
Keyword(s):  
Guanylate Cyclase ◽  
Cyclase Activity ◽  
Human Thyroid ◽  
Thyroid Cell ◽  
Camp Production ◽  
Thyroid Cells ◽  
Guanylate Cyclase Activity ◽  
Low Concentrations ◽  
Camp Levels ◽  
Stimulation Of

Abstract. Forskolin, at 10−11 m, stimulates guanylate cyclase activity in primary human thyroid cell cultures, but does not modify cAMP accumulation. At a 10-fold higher concentration it still stimulates guanylate cyclase activity and becomes an inhibitor of cAMP production. Above 10−9 m, forskolin stimulation of cGMP decreases, while it also becomes a stimulator of cAMP production. There is an additive effect of TSH and forskolin on cAMP production at concentrations of the diterpene which are stimulatory. Concentrations of forskolin which are inhibitory for cAMP, but stimulatory for cGMP, are inhibitory for TSH stimulation of cAMP. The addition of 8-bromo-cGMP duplicates the forskolin effect at low concentrations.

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