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PubMed2003

Inositol phosphate stimulation by LH requires the entire alpha Asn56 oligosaccharide.

Lentil lectin-bound, fucose-enriched hTSH was reported to stimulate both cAMP and inositol phosphate (IP) intracellular signalling pathways, whereas fucose-depleted hTSH stimulated only the cAMP pathway. Gonadotropins activate the cAMP pathway and in several studies higher concentrations activate the IP pathway. Since only the 10% of alpha subunit Asn(56) oligosaccharides (Asn(52) in humans) are fucosylated, the higher glycoprotein hormone concentrations required for IP pathway activation might be related to the abundance of competent hormone isoforms. Lentil lectin-fractionated equine (e)LHalpha and eFSHalpha preparations were combined with a truncated, des(121-149)eLHbeta preparation. All four hybrid hormone preparations induced IP accumulation in porcine theca cells, suggesting that activation of the IP pathway was not dependent on fucosylation at alpha subunit Asn(56). However, the presence of Asn(56) carbohydrate was necessary for increased IP accumulation. Intact, rather than Asn(56)-deglycosylated eLH preparations provoked a biphasic steroidogenic response by rat testis Leydig cells, suggesting that Galpha(i) stimulation was also sensitive to loss of Asn(56) carbohydrate. While rat granulosa cells responded to human FSH preparations in a biphasic manner, a classical sigmoidal response was obtained to eFSH and Asn(56)-deglycosylated eFSH, suggesting that the equine preparations did not activate Galpha(i). Purified oLHalpha Asn(56) oligosaccharides inhibited FSH-stimulated steroidogenesis in rat granulosa cell cultures indicating a direct role for carbohydrate in FSH action. The same carbohydrate preparation inhibited hCG-stimulated fluorescence energy transfer suggesting oligosaccharide involvement in activated LH receptor self-association.

Animals↗
PubMed1994

Mechanisms underlying AlCl3 inhibition of agonist-stimulated inositol phosphate accumulation. Role of calcium, G-proteins, phospholipase C and protein kinase C.

Possible mechanisms of AlCl3-induced inhibition of agonist-stimulated inositol phosphate (IP) accumulation were investigated using rat brain cortex slices, synaptosomes or homogenates. Under conditions in which AlCl3 inhibits carbachol (CARB)-stimulated IP accumulation (Gp-mediated), AlCl3 did not affect CARB (100 microM)-induced decreases (Gi-mediated) in 30 microM forskolin-stimulated cAMP accumulation, suggesting that AlCl3 may be specific for Gp-mediated signal transduction. To determine whether AlCl3 interfered with Gp function and/or phosphatidylinositol-specific phospholipase C (PiPLC) activity, effects of AlCl3 on CARB- and Ca(2+)-stimulated IP accumulation were examined in cortical synaptosomes. AlCl3 (500 microM) decreased CARB (1 mM)- and Ca2+ (20 microM ionomycin)-stimulated IP accumulation to 77 and 75% of control, respectively, suggesting that AlCl3 may not directly affect Gp activity, but does inhibit PiPLC activity. In cortical homogenates, AlCl3 (10-500 microM) inhibited hydrolysis of [3H]phosphatidylinositol 4,5-bisphosphate (PIP2) by PiPLC in a concentration-dependent manner with an estimated IC50 of 100 microM. The effects of AlCl3 on modulation of IP accumulation by extracellular Ca2+ and PKC were also examined as potential mechanisms. Decreasing the extracellular Ca2+ concentration ([Ca2+]e) from 1.0 to 0.1 mM decreased CARB-stimulated IP accumulation in slices. AlCl3 (500 microM) decreased significantly 1 mM CARB-stimulated IP accumulation in 1.0 and 0.1 mM Ca2+ solutions; however, the effect of AlCl3 on IP accumulation did not depend on [Ca2+]e. In cortical slices, inhibition of 1 mM CARB-stimulated IP accumulation by 500 microM AlCl3 was not altered by the PKC activator phorbol 12,13-dibutyrate (PdBu, 1 microM), or the PKC inhibitor H-7 (10 microM), suggesting that AlCl3 does not interfere with IP accumulation by activation of PKC. Other studies found that AlCl3 (10-100 microM) inhibited PKC activity in a concentration-dependent manner in both cytosolic and membrane fractions of cortical homogenates with an estimated IC50 of 60 microM. These results support the hypothesis that AlCl3 inhibition of agonist-stimulated IP accumulation may be mediated by inhibition of PiPLC activity, rather than disruption of G-protein function or modulation of the IP signalling system by Ca2+ or PKC.

Aluminum Chloride↗
PubMed1994

An inositol phosphate glycan derived from a Trypanosoma brucei glycosyl phosphatidylinositol promotes protein dephosphorylation in rat epididymal adipocytes.

Some of the acute actions of insulin may be mediated by an enzyme-modulating inositol phosphate glycan, produced by the insulin-sensitive hydrolysis of a glycosyl phosphatidylinositol that is structurally similar to a membrane protein anchor. An inositol glycan fragment from the structurally characterized Trypanosoma brucei variant surface glycoprotein glycosyl phosphatidylinositol anchor inhibits isoproterenol-stimulated lipolysis in intact rat epididymal adipocytes in a manner mechanistically similar to that of insulin. To explore these effects in more detail, we evaluated the effects of this glycan on protein phosphorylation. Isoproterenol stimulates the phosphorylation of a 70-kilodalton (kDa) protein in these cells. Like insulin, the glycan fragment specifically attenuates the phosphorylation state of the phosphoprotein. In purified adipocyte cytosol, the glycan stimulates the dephosphorylation on serine residues of a 70-kDa protein in a time- and dose-dependent fashion. The glycan-dependent dephosphorylation of the 70-kDa phosphoprotein is unaffected by addition of trifluoroperazine, an inhibitor of serine/threonine phosphatase-2B, but is blocked by the addition of okadaic acid, an inhibitor of serine/threonine phosphatase-1 and -2A. The differential sensitivities of this dephosphorylation reaction to polycations, which activate phosphatase-2A, and phosphorylated inhibitor 1, which blocks phosphatase-1, suggest that dephosphorylation of the 70-kDa protein results from the specific activation of a type 1 serine/threonine phosphatase in adipocytes, providing a mechanistic basis for the insulin-mimetic effects of the inositol glycan.

Adipocytes↗
PubMed1988

Phorbol ester modulates serotonin receptor-mediated increases in inositol phosphate production and calcium mobilization in cultured rat vascular smooth muscle cells.

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on serotonin-induced inositol phosphate (IP) accumulation and intracellular free Ca2+ concentrations [( Ca2+]i) was investigated in cultured rat vascular smooth muscle cells. Pretreatment with TPA had no effect on basal levels of both IP production and [Ca2+]i, whereas it significantly attenuated serotonin-induced increases in both IP production and [Ca2+]i. These data suggest that protein kinase C is involved in the negative feedback control of serotonin-induced rises in both IP production and [Ca2+]i.

Animals↗
PubMed1990

Effect of the kinase inhibitor, H-7, on stress, crossbridge phosphorylation, muscle shortening and inositol phosphate production in rabbit arteries.

Smooth muscle contractile agents cause large increases in crossbridge phosphorylation (Mp) and cycling rates resulting in the rapid development of stress (force/muscle cross-sectional area). Despite temporal declines in Mp and cycling during continued activation, stress is maintained at high levels. This observation led to several different hypotheses describing the regulation of steady-state stress. One proposal is that protein kinase C regulates stress maintenance, whereas another invokes a steady-state dependence on Ca+(+)-calmodulin-dependent myosin light chain kinase. The aim of this study was to investigate the mechanism of stress-maintenance by analyzing the inhibitory efficacy of a protein kinase C inhibitor, H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperizine], on steady-state values of stress, Mp and crossbridge cycling in rabbit renal and femoral arteries. H-7 effectively inhibited steady-state stress produced by KCl (IC50 = 3.7-4.4 microM) and phenylephrine (PhE) (IC50 = 10.6-15.2 microM). Likewise, increases in the level of Mp and the rate of crossbridge cycling induced by both KCl and PhE were significantly reduced by 10 microM H-7. H-7 did not reduce inositol phosphate production stimulated by PhE, but did reduce early stress development thought to be mediated by inositol phosphate-induced mobilization of intracellular calcium. Calcium-induced increases in stress and Mp produced in saponin-skinned artery strips were reduced by less than 50% by 320 microM H-7.(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Hydrolysis of inositol phosphates by plant cell extracts.

A gel-filtered soluble fraction prepared from suspension-cultured Nicotiana tabacum cells hydrolysed inositol mono-, bis- and tris-phosphates. At a concentration of 7.5 microM the rates of hydrolysis followed the sequence Ins(1,4,5)P3 greater than Ins(1,4)P2 greater than Ins(4)P congruent to Ins(1)P. The major products of Ins(1,4,5)P3 hydrolysis identified by h.p.l.c. were Ins(1,4)P2 and Ins(4,5)P2. Ins(1,4)P2 was hydrolysed exclusively to Ins(4)P. The inclusion of Ca2+ in the incubation buffer markedly stimulated the hydrolysis of all the inositol phosphate substrates. Under identical conditions, Ca2+ inhibited the hydrolysis of inositol phosphates by soluble extracts prepared from rat brain. Half-maximal stimulation of Ins(1,4)P2 hydrolysis was obtained at free [Ca2+] of 0.6 and 1.2 microM when the Mg2+ concentration in the incubations was 0.3 and 1.0 mM respectively. This effect of Ca2+ was exerted solely by increasing the Vmax. of hydrolysis without affecting the Km for Ins(1,4)P2. Again, in contrast with brain, the hydrolysis of inositol bis- or mono-phosphates was insensitive to high concentrations of Li+. We conclude that plants contain specific Li+-insensitive inositol phosphate phosphatases that are regulated by low concentrations of Ca2+ in a manner which is different from that observed in mammalian tissues.

Calcium↗
PubMed1987

The relationship between gonadotropin-releasing hormone-stimulated luteinizing hormone release and inositol phosphate production: studies with calcium antagonists and protein kinase C activators.

The coupling between GnRH-stimulated phosphoinositide (PI) turnover and LH release has been investigated in rat pituitary cell cultures. Accumulation of [3H]inositol phosphates ([3H]IPs) formed by hydrolysis of PIs was measured in cells that had been preloaded with [3H]myo-inositol. GnRH stimulated both LH release and incorporation of [3H]inositol into total [3H]IPs with similar dose and time dependencies. [3H] IP production in response to GnRH could be blocked by a GnRH antagonist, but was stimulated by a compound that provokes receptor microaggregation. GnRH-stimulated IP production persisted in the presence of either the Ca2+ channel blocker D600 or the calmodulin antagonist pimozide at concentrations that reduced LH release to 60% and 20% of control, respectively. Stimulated [3H]IP production was inhibited at higher concentrations of D600. In 1-h incubations, GnRH-stimulated [3H]IP production, but not LH release, was markedly inhibited by the protein kinase C activators phorbol myristate acetate and 1,2-dioctanoylglycerol. These findings indicate that in the gonadotrope, GnRH-stimulated LH release and [3H]IP production are closely coupled to receptor activation by an agonist; Ca2+ antagonists uncouple stimulated LH release from [3H]IP production; and protein kinase C activators uncouple stimulated PI turnover from LH release. Thus, GnRH-stimulated production of PI metabolites, as measured by [3H]IP accumulation, is apparently not sufficient to support LH release in the absence of Ca2+. In addition, GnRH-stimulated LH release is apparently not dependent on full expression of the PI response.

Animals↗
PubMed1990

A M3 muscarinic receptor coupled to inositol phosphate formation in the rat cochlea?

Various neuroactive substances, including excitatory and inhibitory amino acids, biogenic amines and neuropeptides, were tested for their ability to stimulate the inositol phosphate (IPs) cascade in the presence of lithium in the rat cochlea. Among them, only the muscarinic agonists (carbachol and oxotremorine M) were able to stimulate the IPs formation in 12-day-old rat cochleas. The carbachol-elicited IPs formation was inhibited by muscarinic antagonists with the following relative order of potency: atropine greater than 4-DAMP much greater than pirenzepine greater than methoctramine = AF-DX 116. This pharmacological profile suggests that the activation of the M3 muscarinic receptor subtype is responsible for the increase in IPs synthesis in the rat cochlea. However, an interaction with a m5 receptor subtype could not be completely excluded. The unusual link of only one receptor subtype with the phosphoinositide breakdown in the cochlea, as opposed to the usual existence of several receptors coupled to this transduction system in other organs such as the brain, suggest a unique role for muscarinic agonists in the cochlea.

Animals↗
PubMed1992

An inositol phosphate glycan derived from a Trypanosoma brucei glycosyl-phosphatidylinositol mimics some of the metabolic actions of insulin.

Some of the acute actions of insulin may be mediated by an enzyme-modulating inositol phosphate glycan, produced by the insulin-sensitive hydrolysis of glycosyl-phosphatidylinositol (GPI) that is structurally similar to a membrane protein anchor. An inositol glycan fragment from the structurally characterized Trypanosoma brucei variant surface glycoprotein GPI anchor is evaluated for insulin-mimetic antilipolytic activity. The fragment specifically and dose-dependently inhibits isoproterenol-stimulated lipolysis. Like the effect of insulin, glycan-induced antilipolysis is blocked by the low Km cAMP phosphodiesterase inhibitor imazodan (CI-914) and the serine/threonine phosphatase inhibitor, okadaic acid, suggesting that the activation of both cAMP phosphodiesterase and serine/threonine protein phosphatases are necessary. Moreover, this fragment causes a specific and dose-dependent inhibition of both microsomal glucose-6-phosphatase (EC 3.1.3.9) and cytosolic fructose-1,6-bisphosphatase (EC 3.1.3.11) activity. Additionally, direct addition of the glycan to hepatocytes caused marked inhibition of glucose production from pyruvate. These results suggest that the direct modification of the activities of these two gluconeogenic enzymes by an inositol glycan may play a role in the inhibition of glucose output by insulin and provide the first evidence for the insulin-mimetic properties of a chemically characterized inositol glycan.

Adipose Tissue↗
PubMed1986

Neomycin inhibits inositol phosphate formation in human platelets stimulated by thrombin but not other agonists.

Neomycin (0.1-1 mM) added to human platelet-rich plasma or washed platelets prelabeled with [3H]inositol inhibits aggregation, ATP secretion (ID50 0.2 mM) and formation of [3H]inositol mono-, bis- and trisphosphate (ID50 0.6-0.8 mM) in response to thrombin (0.25 U/ml). The production of inositol phosphates in response to other platelet agonists (vasopressin, platelet activating factor, prostaglandin endoperoxide analogs and collagen) is not inhibited by neomycin, even at a concentration of 2 mM. At this concentration neomycin reduces the secretion of ATP stimulated by these agents (by up to 50%). The results indicate that neomycin has multiple effects on platelets that are unrelated to a specific inhibition of inositol phospholipid degradation by phospholipase C. Low concentrations (0.1-1 mM) of neomycin might selectively inhibit the interaction of thrombin with the platelet surface, and high concentrations (greater than 2 mM) might unspecifically reduce platelet secretion in response to various platelet agonists.

Adenosine Triphosphate↗
PubMed1987

Further evidence for a phospholipase C-coupled G protein in hamster fibroblasts. Induction of inositol phosphate formation by fluoroaluminate and vanadate and inhibition by pertussis toxin.

We have previously reported that alpha-thrombin induces in resting hamster fibroblasts (CCL39) the formation of inositol phosphates (IP) by activating a GTP-binding protein (G protein) sensitive to pertussis toxin (Paris, S., and Pouysségur, J. (1986) EMBO J. 5, 55-60). Here we show that IP formation in CCL39 cells can also be induced by NaF with AlCl3 and by vanadate. In the presence of Li+, IP accumulation is linear over 30 min with no detectable lag and is concentration-dependent. NaF alone is slightly stimulatory, but a marked potentiation is observed in the presence of AlCl3, by itself without effect. Maximal stimulation is obtained with 10 mM NaF and 3 microM AlCl3, and with vanadate half-maximal effect is achieved at 0.3 mM. Both stimulations are markedly inhibited (up to 80%) by pertussis toxin (half-maximal inhibition at 1-2 ng/ml). We therefore conclude that phospholipase C is stimulated by NaF plus AlCl3 (presumably acting as AlF-4) and by vanadate by direct activation of the regulatory G protein. In addition, NaF inhibits the inositol-1-phosphatase, but this effect is not potentiated by AlCl3. Similarly, vanadate inhibits inositol trisphosphate degradation. Maximal stimulations of phospholipase C by AlF-4 and vanadate are not additive, whereas they are both additive with thrombin effects. Pretreatment of cells for 15 min with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate nearly completely abolishes induction of IP formation by AlF-4 and vanadate, suggesting that protein kinase C exerts a feedback negative control either on the G protein or on phospholipase C itself. An increase in cellular cyclic AMP similarly results in a marked attenuation of AlF-4-induced IP formation, indicating that activation of phospholipase C can be controlled also by cyclic AMP. However, the stimulatory effect of AlF-4 on phospholipase C is clearly dissociated from its effect on the adenylate cyclase system.

Adenylate Cyclase Toxin↗
PubMed2002

Effect of bremazocine, a kappa-opioid receptor agonist, on inositol phosphate formation in isolated iris-ciliary bodies.

The goal of the current study was to examine the effect of the kappa-opioid agonist, bremazocine (BRE), on inositol phosphate (IP) formation in the rabbit iris-ciliary body (ICB). Concentrations of BRE (10(-7) to 10(-5) M) augmented levels of IP. Incubation of ICBs with BRE (10(-6) M) produced a time-dependent increase in IP levels that peaked at 60 s and declined to basal levels by 5 min. The increase in IP levels produced by BRE (10(-6) M) was inhibited by the kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI, 10(-7) to 10(-5) M) and by activation of PKC with PDBu (10(-7) M). These results demonstrate that kappa-opioid receptor activation by BRE in the rabbit ICB is linked to IP production. Thus, opioid agonist-induced increases in IP activity could play a role in BRE-induced increases in atrial natriuretic peptide release and alterations in aqueous humor dynamics.

Animals↗
PubMed1993

Effects of excitatory amino acids on inositol phosphate accumulation in slices of the cerebral cortex of young and aged rats.

The effects of glutamate, NMDA and quisqualate on carbachol- and norepinephrine-elicited formation of inositol phosphate (IP) were evaluated in slices prepared from the cerebral cortex of 3- and 24-month Sprague-Dawley rats. Glutamate, NMDA, and quisqualate antagonized the IP response to carbachol in a concentration-dependent fashion. This antagonism was more pronounced in aged than in young rats, both for glutamate (IC5O 0.114 and 0.210 mM) and NMDA (IC5O 0.0029 and 0.127 mM), but not for quisqualate. Glutamate (but not NMDA) also antagonized in a concentration-dependent fashion the IP response to norepinephrine, IC50s were 0.061 and 0.126 mM for aged and young rats, respectively; quisqualate had an inhibitory effect only at 1 mM concentration in the two age-groups, while in aged rats some stimulatory effect was present at 0.1 mM concentration. Glutamate, NMDA and quisqualate (1 mM) did not affect basal IP accumulation in either young or aged rats; quisqualate, however, at 0.1 mM concentration had some stimulatory effect, more pronounced in aged rats. This effect was probably responsible for the biphasic effect of quisqualate in this age-group. The most important finding consists of the demonstration of an age-related increase in the inhibitory effects of NMDA on carbachol-induced IP accumulation. This implies an altered modulation of cholinergic post-receptor mechanisms by glutamatergic mechanisms.

Aging↗
PubMed1991

The role of the inositol phosphate cascade in visual excitation of invertebrate microvillar photoreceptors.

The identity of the transmitter(s) involved in visual transduction in invertebrate microvillar photoreceptors remains unresolved. In this study, the role of inositol 1,4,5-trisphosphate (IP3) was examined in Limulus ventral photoreceptors by studying the effects on the light response of heparin and neomycin, agents that inhibit the production or action of IP3. Both heparin and neomycin reduce responses to brief flashes of light and the transient component of responses to steps of light, and also inhibit IP3-induced calcium release, indicating that IP3 plays a direct role in invertebrate visual excitation. The effects of BAPTA, a calcium buffer, were also examined and shown to be consistent with a role for IP3-mediated calcium release in visual excitation. However, all three agents fail to block the plateau component of the response to a step of light, indicating that a single pathway involving IP3 and calcium cannot solely be responsible for visual excitation in invertebrates. We suggest that the inositol phosphate cascade and a second parallel process that is not dependent on IP3 are involved in the production of the light response.

Animals↗
PubMed1990

Is the adenosine receptor modulation of histamine-induced accumulation of inositol phosphates in cerebral cortical slices mediated by effects on calcium ion fluxes?

In this report, we show that under conditions designed to provide an initially uniform incorporation of [3H]inositol into mouse and guinea pig cerebral cortical slices prior to agonist stimulation, the accumulation of 3H-inositol phosphates (3H-InsPx, x = 1-4) induced by histamine in mouse and guinea pig cerebral cortical slices increased in a quasilinear manner with increasing added calcium. Raising the ambient calcium ion concentration failed to reduce the adenosine receptor-mediated inhibition of the histamine-induced 3H-InsPx response in mouse cerebral cortical slices. Similarly, the potentiation of the histamine response by adenosine receptor activation in guinea pig cerebral cortical slices was unaffected by lowering the added calcium ion concentration. The presence of the calcium ionophore A23187 (33 microM) produced 3H-InsPx responses in both mouse and guinea pig cerebral cortical slices, which were not affected by the presence of the stable adenosine analogue 2-chloroadenosine. A23187 also potentiated the accumulation of 3HInsPx induced by histamine in both species. Both the inhibitory and potentiatory modulations of the histamine response by 2-chloroadenosine in mouse and guinea pig, respectively, were still apparent in the presence of A23187. These results indicate that the histamine-induced 3H-InsPx accumulations in both mouse and guinea pig cerebral cortical slices are sensitive to variations in calcium ion concentrations. However, the adenosine receptor modulations of the histamine responses are relatively insensitive to fluctuations in either extra- or intracellular calcium ion concentrations, and thus cannot be mediated by effects on calcium ion movements.

2-Chloroadenosine↗
PubMed1995

Inositol phosphate release and metabolism in rat left atria.

The phosphatidylinositol (PtdIns) turnover pathway in intact heart tissue differs from that in most cell types in that products of the inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] kinase pathway are not detected in 3H-labeling studies. In contrast, Ins(1,4,5)P3 kinase products are detected in isolated neonatal cardiomyocytes. To understand the basis for the observed properties of the cardiac pathway, a detailed study of inositol phosphate (InsP) release has been undertaken by using isolated adult rat left atria. Addition of norepinephrine to 3H-labeled atria caused a slow increase in 3H-labeled Ins(1,4,5)P3 and a more rapid increase in 3H-labeled Ins(1,4)P2, its immediate dephosphorylation product. The mass of Ins(1,4,5)P3 was high in unstimulated atria (13.5 +/- 1.1 pmol/mg tissue, mean +/- SEM, n = 4) and did not change with stimulation. Measurements of the specific activities of Ins(1,4,5)P3 and PtdIns(4,5)P2 provided an estimate of the turnover rate of Ins(1,4,5)P3 that was 20- to 40-fold lower than the rate of accumulation of 3H label in InsP1 and InsP2. In agreement with this, specific activities of InsP1 and InsP2 were higher than the specific activity of InsP3 in both control and stimulated atria. Neomycin (5 mmol/L) did not inhibit the accumulation of 3H-labeled InsP1 and InsP2 in left atria, even though it reduced the accumulation of 3H label in Ins(1,4,5)P3, providing evidence that InsP1 and InsP2 do not derive primarily from Ins(1,4,5)P3. Stimulation with norepinephrine for 20 minutes resulted in a parallel decrease in 3H-labeled Ins(1,4,5)P3 and in Ins(1,4,5)P3 mass, demonstrating that atria do not contain two different pools of Ins(1,4,5)P3.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Bradykinin stimulation of inositol phosphate and calcium responses in insensitive to pertussis toxin in NG115-401L neuronal cells.

Stimulation of NG115-401L neuronal cells with bradykinin produces a dose-dependent increase in inositol phosphate production which is not blocked, rather slightly increased, after treatment with pertussis toxin. Nevertheless, pertussis toxin stimulates ADP-ribosylation of a 41K membrane protein, and blocks opioid receptor-mediated inhibition of stimulated cAMP production in these cells. These results suggest that bradykinin responses in the NG115-401L cells are pertussis-insensitive, unlike bradykinin responses reported in other neuronal cell lines.

Adenosine Diphosphate Ribose↗