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J Christophe

Publications and source records attributed to J Christophe.

At least 163 records · Page 9Linked to original sources
PubMed1984

Multiple effects of short-chain alcohols on binding to rat heart muscarinic receptors.

Short-chain alcohols inhibited the equilibrium binding of agonists and antagonists to rat heart muscarinic receptors. Methanol, ethanol, propan-2-ol and propan-1-ol, when used at low concentrations, behaved as pseudo-competitive antagonists. Their rank order of potency paralleled their relative partition coefficients, suggesting that this inhibition was simply due to the interaction of the alcohols with a hydrophobic part of the receptor or with membrane lipids. The four alcohols increased the dissociation rate constant of [3H]oxotremorine M from the high-affinity agonist receptors and decreased the stability of this receptor state. These effects might reflect increased membrane fluidity and/or decreased hydrophobic interactions (see below). By contrast, the effects of alcohols on the association and dissociation rates of N-[3H]- methscopolamine (an antagonist) were not correlated to their relative octanol/water partition coefficient (a measure of their affinity for biophases ). Alcohols, at the relatively high concentrations necessary for increased membrane 'fluidity', are known to affect the relative stability of various protein conformations. We believe that the effects of alcohols on antagonist binding to rat heart muscarinic receptors reflected changes in the activation energy of association and dissociation reactions, the inhibition of equilibrium binding being mainly due to decreased 'hydrophobic interactions'.

1-Propanol↗
PubMed1984

Purification of a novel pancreatic secretory factor (PSF) and a novel peptide with VIP- and secretin-like properties (helodermin) from Gila monster venom.

A combination of three HPLC procedures applied to the venom of Gila monster (Heloderma suspectum) has led to the purification to homogeneity of two bioactive components: (i) a 17.5 kDa protein, isolated on the basis of its potent secretory effect on dispersed rat pancreatic acini, was accordingly designated PSF (pancreatic secretory factor); (ii) a 5.9-kDa peptide, designated helodermin, was purified on the basis of its ability to stimulate adenylate cyclase in rat pancreatic membranes. PSF was unable to activate adenylate cyclase and, conversely, helodermin was devoid of secretory action.

Adenylyl Cyclases↗
PubMed1984

Evidence that helodermin, a newly extracted peptide from Gila monster venom, is a member of the secretin/VIP/PHI family of peptides with an original pattern of biological properties.

Helodermin, a newly isolated peptide from the venom of Gila monster (Heloderma suspectum) was shown to stimulate the adenylate cyclase activity of rat pancreatic membranes as efficiently as secretin and VIP. It also increased cyclic AMP levels and inhibited [125I]VIP binding in rat pancreatic acini. Finally, helodermin activated adenylate cyclase in membranes from rat heart, rat brain, and human heart, showing properties analogous yet distinct from those of secretin, VIP and PHI.

Adenylyl Cyclases↗
PubMed1984

Pancreatic secretory factor (PSF), a protein from Gila monster venom stimulating enzyme secretion from rat pancreatic acini.

Pancreatic secretory factor (PSF), a 17.5-kDa protein purified from the venom of Gila monster (Heloderma suspectum), stimulated amylase secretion from dispersed rat pancreatic acini more efficiently than CCK-8, bombesin, carbachol and secretin, and without increasing 45Ca2+ efflux and cyclic AMP levels. The secretory action was dependent on the presence of extracellular calcium and was additive to the secretion induced by agents acting via cyclic AMP or via Ca2+ efflux.

Amylases↗
PubMed1984

Characterization of muscarinic cholinergic receptors on rat pancreatic acini by N-[3H]methylscopolamine binding. Their relationship with calcium 45 efflux and amylase secretion.

N-[3H]Methylscopolamine (NMS) binding, amylase secretion, and 45Ca efflux from dispersed rat pancreatic acini were investigated in parallel, in the presence or absence of 4 muscarinic agonists and 3 muscarinic antagonists. Scatchard analysis of [3H]NMS saturation isotherms gave a KD of 0.9 nM and an average binding capacity of 24,000 sites per cell. Binding competition curves with the antagonists atropine, dexetimide, and NMS gave KD values of 3.5, 3.5, and 0.5 nM, respectively. With the 3 full agonists oxotremorine, muscarine, and carbamylcholine, the receptor population could be divided into two classes of binding sites: a minor one (15%) with high affinity (KD = 20-35 nM) and a major one (85%) with low affinity (KD = 3-65 microM). There was a receptor reserve of about 50% with respect to carbamylcholine-stimulated amylase secretion. Further analysis of dose-effect curves suggests that low affinity binding sites were involved in the secretory response to muscarinic stimulation. Pilocarpine, like muscarinic antagonists, recognized all binding sites with the same affinity but acted as a partial agonist on amylase secretion and 45Ca efflux.

Amylases↗
PubMed1984

A comparison between muscarinic receptor occupancy, adenylate cyclase inhibition, and inotropic response in human heart.

Binding to muscarinic receptors was compared with adenylate cyclase inhibition in membranes derived from human heart auricles, and with inhibition of the contraction of auricular muscle fibers. In the absence of GTP, agonists recognized two classes of receptors both of which bound antagonists with the same affinity. In the presence of GTP, both classes of receptors for agonists were converted into a single low affinity state. Carbachol and oxotremorine inhibited adenylate cyclase activity by 43%, pilocarpine being less efficient (-28%). The 3 agonists exerted similar inhibitory effects on the inotropic response, in 7 out of 9 preparations of electrically- and norepinephrine-stimulated fibers. Dose-effect curves suggested that spareness (or an amplification mechanism) was implicated in the occupancy of low affinity binding sites by carbachol and oxotremorine (but not by the partial agonist pilocarpine) and the resulting inhibition of both adenylate cyclase activity and contractile force.

Adenylyl Cyclase Inhibitors↗
PubMed1984

Secretin-induced changes in rate, contractility and adenylate cyclase activity in rat heart atria.

Secretin stimulated adenylate cyclase activity in crude membrane preparations from right and left rat atria, when tested in the presence of the potentiating activator forskolin. Its maximal effect on adenylate cyclase activity was greater in the right atrium than in the left atrium but the peptide efficiency was lower, in both atria, than that of D,L-isoproterenol. Secretin stimulated the rate of contraction of the spontaneously beating right atrium, but less efficiently than D,L-isoproterenol. Although this positive chronotropic action of secretin was inhibited by D,L-propranolol, it was probably not mediated by the release of endogenous catecholamines as: a) the inhibitory effects of D- and L-propranolol were similar and b) the efficiency of secretin on the in vitro beating of right atrium was the same in control and reserpinized rats. Secretin stimulated the force of contraction of spontaneously beating right atrium, even in the presence of propranolol, i.e. when the chronotropic effect of secretin was abolished. The hormone exerted also a positive inotropic effect on the electrically stimulated rat atrium. This effect was blocked neither by tetrodotoxin nor by propranolol. When comparing the dose-effect curves of secretin and D,L-isoproterenol on adenylate cyclase activation on the one hand, and on the stimulation of rate and contractility on the other hand, it is tempting to suggest that cyclic AMP might be involved in the modulation by secretin of the mechanical properties of rat atria.

Adenylyl Cyclases↗
PubMed1984

The in vitro chronotropic and inotropic effects of vasoactive intestinal peptide (VIP) on the atria and ventricular papillary muscle from Cynomolgus monkey heart.

The in vitro chronotropic and inotropic effects of vasoactive intestinal peptide (VIP) and of isoproterenol, two agents known to stimulate cardiac adenylate cyclase were compared on the heart from Cynomolgus monkey using the spontaneously beating right atrium, the electrically stimulated left atrium, and the electrically-stimulated ventricular papillary muscle. VIP increased concentration-dependently the rate of beating of the right atrium as well as the contractility of both atria but its efficiency was lower than that of D,L-isoproterenol. VIP also stimulated concentration-dependently, and this time as efficiently as D,L-isoproterenol, the contractility of papillary muscle. These VIP effects were unaltered by the neuronal blocker tetrodotoxin. In addition, the moderate inhibition exerted by the beta-adrenergic blocker D,L-propranolol on VIP effects argued against the implication of beta-adrenergic receptors in VIP effects. These results indicate that VIP exerts a direct stimulatory influence on the rate and contractility of Cynomolgus monkey heart.

Animals↗
PubMed1983

Effect of pH on binding of agonists and antagonists to rat heart muscarinic receptors.

The pH-dependence of antagonist and agonist binding to rat heart muscarinic receptors was investigated at 25 degrees C, in the absence and in the presence of GTP. The small inhibitory effect observed at the lowest pH investigated (pH 6.0) on [N-methyl-3H]methscopolamine chloride and [methyl-3H]oxotremorine-M acetate binding indicated that one or more amino acid residues of the receptor had to be deprotonated for optimal binding affinity. The low pK value of these residues (between 5 and 6) prevented their identification. The binding of scopolamine (pK 7.6) was favoured by a positive charge in the titratable amine, but binding with a lower affinity remained possible charge in the titratable amine, but binding with a lower affinity remained possible without this charge. GTP did not affect antagonist binding at any pH, but converted more than 90% of agonist binding sites into a low affinity conformation. In the absence of GTP, we observed a time- and pH-dependent conversion of the super-high- and high-affinity receptors to a low-affinity GTP-insensitive state. This conversion was markedly accelerated at high pH (above pH 8.0). In the presence of GTP, a positive charge on the titratable amine of pilocarpine (pK 7.05) and oxotremorine (pK 8.60) was required for binding. These results support the view that antagonist (e.g. methscopolamine) binding to receptors was largely facilitated by hydrophobic interactions, whereas agonist binding to low-affinity sites was mainly driven by ionic interactions.

Animals↗
PubMed1983

The adenylate cyclase activity in heart membranes from normotensive and spontaneously hypertensive rats, after chemical sympathectomy, suggests the presence of presynaptic secretin receptors.

Normotensive (WKY) and spontaneously hypertensive (SHR) male adult rats were sacrificed 2 and 3 weeks after 6-hydroxydopamine treatment. Untreated WKY and SHR rats served as controls. In rat heart membranes from WKY rats, 6-hydroxydopamine treatment increased guanosine 5'-O-(2-3-imido)-triphosphate (Gpp(NH)p)-, NaF-, D,L-isoproterenol- and glucagon-stimulated adenylate cyclase activities by 18-38% while secretin stimulation was unaffected. In heart membranes from SHR rats, Gpp(NH)p, NaF, D,L-isoproterenol, or glucagon stimulation of the enzyme was similarly increased by 14-38% whilst the low secretin responsiveness which is characteristic of these animals decreased even further (by 24-47%). These results are consistent with: (1) an up regulation of postsynaptic beta-adrenergic receptors coupled to adenylate cyclase after degeneration of adrenergic nerves, and (2) a differential response of secretin receptors coupled to adenylate cyclase in the two strains of rats: there was no change in WKY rats and a decreased response in SHR rats. The possible presence and contribution of presynaptic secretin cardiac receptors is considered.

Adenylyl Cyclases↗
PubMed1983

Inhibitory effects of pirenzepine on muscarinic stimulation of rat pancreas.

The binding properties and pharmacological effects of pirenzepine were compared to those of atropine in isolated pancreatic acini and pancreatic membranes of rats. In the first preparation, pirenzepine and atropine blocked [N-methyl-3H]scopolamine ([3H]NMS) binding, pirenzepine being 110 times less potent than atropine (KD for pirenzepine 0.38 microM and for atropine 3.5 microM). A similar difference in potency was observed with respect to carbamylcholine stimulation of amylase secretion (IC50 for pirenzepine 4.5 microM and for atropine 30 nM) and calcium efflux (IC50 for pirenzepine 2.8 microM and for atropine 4 nM). Correspondingly, in rat pancreatic membranes, the KD values for pirenzepine and atropine were 250 and 1.5 nM, respectively. These data are compatible with the hypothesis that the in vitro antimuscarinic effect of pirenzepine on the rat pancreas is linked to the occupancy of a single homogeneous class of receptors with a low affinity for the antagonist.

Animals↗
PubMed1983

Conversion of orally administered 2-n.pentylaminoacetamide into glycinamide and glycine in the rat brain.

Male Sprague Dawley albino rats were treated orally with 2-n.pentylaminoacetamide (10 to 100 mg/kg b.wt). This oral administration provoked a dose-related and time-dependent accumulation of glycinamide in forebrain, cerebellum, and medulla, and to increased levels of glycine in the three brain areas, and of serine in medulla. In kidney, liver and plasma, the accumulation of glycinamide was lower and there was no increase in glycine and serine levels. With a dose of 100 mg/kg b.wt, 28% of the drug were eliminated unchanged and 16% as glycinamide, in urines collected for 24 h. In all tissues examined, 2-n.pentylaminoacetamide and glycinamide levels peaked at 1 h and were nil again after 24 h, the ratio of 2-n.pentylaminoacetamide over glycinamide decreasing more rapidly in brain than in kidney and liver. Contrasting with the effects of 2-n.pentylaminoacetamide, the oral administration of glycinamide (66 mg/b.wt) led, 2 hours later, to similar low rises of glycinamide in plasma and brain. In another control experiment, the intraperitoneal injection of a large dose of glycine (450 mg/kg b.wt) provoked, 30 min later, modest rises of glycine levels in the central nervous system that merely reflected a contamination by plasma glycine.

Administration, Oral↗
PubMed1983

Increased number of high-affinity muscarinic receptors in rat heart after phenylhydrazine treatment.

The effect of phenylhydrazine-induced heart hypertrophy on muscarinic cholinergic binding sites was studied in heart membranes by determining total (with [3H]NMS) and high-affinity (with [3H]Oxo-M) binding sites and estimating low-affinity binding sites by difference. Phenylhydrazine induced an increased concentration of high-affinity binding sites without affecting the concentration of low-affinity binding sites. The KD values for the ligands were unaffected.

Animals↗
PubMed1983

Effects of full and partial beta-adrenergic agonists and antagonists on human lung adenylate cyclase.

The beta-adrenergic stimulation of adenylate cyclase in membranes from human lung was compared to that of adenylate cyclase in membranes with a majority of beta 2-adrenergic receptors (from rat lung) and in membranes with a homogeneous population of beta 2-adrenergic receptors (from rat erythrocytes and reticulocytes). In terms of adenylate cyclase stimulation, three full agonists (isoproterenol, epinephrine and norepinephrine), four partial agonists (procaterol, salbutamol, fenoterol and zinterol), and four antagonists (propranolol, metoprolol, atenolol and practolol) were tested. The potency (Kact or Ki) of the eleven beta-adrenergic agents, and the Hill coefficient (of 1) for the four antagonists tested indicated that the activation of human lung adenylate cyclase occurred through receptors of the beta 2-subtype only. Partial beta-adrenergic agonists were efficiently discriminated by the human lung preparation, as shown by distinct intrinsic activities. The mediocre efficacy and the relatively low potency of all beta-adrenergic agonists on adenylate cyclase suggested a relatively low density of beta 2-adrenergic receptors, as compared to the enzyme density.

Adenylyl Cyclase Inhibitors↗
PubMed1983

Purification and kinetic properties of two soluble forms of calmodulin-dependent cyclic nucleotide phosphodiesterase from rat pancreas.

The calmodulin-dependent cyclic AMP phosphodiesterase and cyclic GMP phosphodiesterase (EC 3.1.4.17) activity of rat pancreas was purified 280-fold by affinity chromatography on calmodulin-Sepharose 4B. It then accounted for 15% of the total cytosol cyclic GMP nucleotide phosphodiesterase activity, in the presence of Ca2+, and represented a minor component of proteins specifically adsorbed by the column. This activity was resolved on a DEAE-Sephacel column into two fractions, termed PI and PII, on the basis of their order of emergence. After this step, PI and PII were purified 5650- and 3700-fold respectively. The molecular weight of PI was 175 000 and that of PII was 116 000, by polyacrylamide-gradient-gel electrophoresis. Both forms of phosphodiesterase could hydrolyse cyclic AMP and cyclic GMP, although PII displayed a higher affinity toward cyclic GMP than toward cyclic AMP. PI and PII exhibited negative homotropic kinetics in the absence of calmodulin. Upon addition of calmodulin, both enzymes displayed Michaelis-Menten kinetics and a 5-9-fold increase in maximal velocity, at physiological concentrations of cyclic GMP and cyclic AMP. When a pancreatic extract freshly purified by affinity chromatography was immediately analysed by high-performance gel-permeation chromatography on a TSK gel G3000 SW column, PII represented as much as 78% of the eluted activity. This percentage decreased to 52% when the sample was stored at 0 degrees C for 20 h before analysis, suggesting that PII, possibly predominant in vivo, was converted into the heavier PI form upon storage.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Monomeric pituitary growth hormone and prolactin variants in man characterized by immunoperoxidase electrophoresis.

Immunoperoxidase electrophoresis, combining SDS--ME--PAGE and the 'double bridge' immunoperoxidase staining was applied to crude human pituitary homogenates. With anti-hGH and anti-hPL sera, 4 hGH-related monomers were characterized: a Mr 22 000 peptide corresponding to hGH; a Mr 20 000 peptide corresponding to the known hGH variant and two unknown hGH variants (Mr 65 000 and Mr 75 000). With anti-ovine, rat and human PRL sera, 4 PRL-related monomers were immunostained: one comigrated with purified hPRL (Mr 25 000), and 3 were unknown (Mr 29 000; Mr 45 000; Mr 16 000).

Aged↗