Degradation of rat brain cholinergic muscarinic receptors in vitro: enhancement by agonists and inhibition by antagonists

Conserved Expression of Nav1.7 and Nav1.8 Contribute to the Spontaneous and Thermally Evoked Excitability in IL-6 and NGF-Sensitized Adult Dorsal Root Ganglion Neurons In Vitro

Sensory neurons respond to noxious stimuli by relaying information from the periphery to the central nervous system via action potentials driven by voltage-gated sodium channels, specifically Nav1.7 and Nav1.8. These channels play a key role in the manifestation of inflammatory pain. The ability to screen compounds that modulate voltage-gated sodium channels using cell-based assays assumes that key channels present in vivo is maintained in vitro. Prior electrophysiological work in vitro utilized acutely dissociated tissues, however, maintaining this preparation for long periods is difficult. A potential alternative involves multi-electrode arrays which permit long-term measurements of neural spike activity and are well suited for assessing persistent sensitization consistent with chronic pain. Here, we demonstrate that the addition of two inflammatory mediators associated with chronic inflammatory pain, nerve growth factor (NGF) and interleukin-6 (IL-6), to adult DRG neurons increases their firing rates on multi-electrode arrays in vitro. Nav1.7 and Nav1.8 proteins are readily detected in cultured neurons and contribute to evoked activity. The blockade of both Nav1.7 and Nav1.8, has a profound impact on thermally evoked firing after treatment with IL-6 and NGF. This work underscores the utility of multi-electrode arrays for pharmacological studies of sensory neurons and may facilitate the discovery and mechanistic analyses of anti-nociceptive compounds.

Mucocutaneous cholinergic system is targeted in mustard-induced vesication

The purpose of this research is to elucidate the pharmacological mechanism mediating vesicating effects of sulfur mustard (HD) and identify an antidote to its action. HD causes blisters because epithelial cells lose their attachments. Epithelial cell adhesion is under control of the local cytotransmitter acetylcholine (ACh) working through the muscarinic and nicotinic receptor, mAChR and nAChR, classes expressed by epithelial cells. In this study, nitrogen mustard (NM)-a structural analog of HD-was used to elucidate the mechanism of vesicating effects of mustards in mucocutaneous tissues. NM caused cell detachment and cholinergic agents antagonized its effect. Radioligand binding inhibition experiments showed that NM binds to the ligand-binding site of ACh receptors (AChRs) of both classes. Ligation of AChRs on the cell membrane of keratinocytes (KC) and bronchial epithelial cells (BEC) with NM increased total esterolytic activity of serine proteinases (TEASP). Antagonists of both classes of AChRs, atropine and mecamylamine, diminished NM-induced changes, suggesting that the pathobiological effects of NM on KC and BEC result from an agonist-like degradation of ligated AChRs, predominantly of the muscarinic class. Thus, biological effects of NM on cell adhesion were antagonist-like, whereas its pharmacological effect on TEASP was agonist-like. These findings support a hypothesis that pharmacologic protection from the vesicating action of HD can be achieved by using cholinergic drugs.

In vitro pharmacological effects of S 12370 (2-[4-benzhydryloxypiperidinoethyl]isoxindole; an antibronchoconstrictor agent) in normal and sensitized tissue

The effects of S 12370 (2-[4-benzhydryloxypiperidinoethyl]isoxindole), were studied in vitro. In guinea pig isolated tracheal rings, S 12370 induced a similar competitive inhibition of the contractile responses produced by acetylcholine, histamine and serotonin. However, it did not affect the contractions induced by leukotriene D4 (LTD4), substance P and U 46619, a stable analogue of thromboxane A2. S 12370 induced a concentration dependent inhibition of the cholinergic component of the contraction induced by electrical field stimulation, whereas it did not influence the sustained nonadrenergic noncholinergic (NANC) excitatory response observed in guinea pig isolated bronchi. S 12370 did not influence the relaxations induced by prostaglandin E2, isoprenaline and salbutamol, and did not modify the nonadrenergic noncholinergic inhibitory response induced by electrical field stimulation. In isolated left atria, the negative inotropic effect of acetylcholine was competitively inhibited by S 12370. In binding experiments, S 12370 exhibited similar affinity for M1, M2, M3, M4 muscarinic receptors and also recognized 5-HT2 serotonin and H1 histamine receptor subtypes. In ovalbumin-sensitized animals, the contractile response of isolated tracheal rings produced by exposure to the allergen was not influenced by S 12370. Tracheal rings from sensitized animals preexposed in vitro to the allergen developed a hyporesponsiveness to beta-adrenoceptor stimulation. S 12370 prevented the inhibitory effect caused by ovalbumin immune sensitization in the relaxation to isoprenaline. In rat polymorphonuclear neutrophil (PMN) cells, S 12370 up to 10(-5) M did not inhibit the arachidonic acid metabolism. These results suggest that in guinea pig tracheal smooth muscle, S 12370 is a competitive inhibitor of muscarinic, serotonin and histamine receptors and can modulate the beta-adrenergic dysfunction induced by immune sensitization. S 12370 may present some therapeutic interest in inflammatory airway diseases.

A water-soluble, stable dipeptide NK1 receptor-selective neurokinin receptor antagonist with potent in vivo pharmacological effects: S18523

The potassium salt of a chemically stabilized dipeptide, {1-[4-(1 H-tetrazol-5-yl)butyl]indol-3-yl}carbonyl-Hyp-Nal-N(methyl)-Bzl , (Hyp = (R)-4-hydroxy-L-proline; Nal = 3-L-(beta-naphthyl)-alanine), S18523, is described as a new water-soluble, potent and selective NK1 receptor antagonist. The low molecular weight antagonist (M(r) = 736) displays nanomolar potency (pA2 = 9.6) in the rabbit vena cava (NK1) bioassay and nanomolar affinity (pKi = 9.1) on the human NK1 receptor expressed by lymphoblastoma cells. It is devoid of mu-opiate affinity (Ki > 10(-4) M with respect to tritiated Tyr-DAla-Gly-MePhe-Gly-ol), has negligible calcium-channel affinity (estimated Ki = 2.6 x 10(-5) M, with respect to isradipine) and does not cause peritoneal mast-cell degranulation. S18523 has strong antinociceptive effects in three classical pain tests in vivo both by i.v. and p.o. routes. The dipeptide potently antagonizes bronchoconstriction provoked by exogenous substance P in the guinea-pig and acts longer than the non-peptide antagonist CP99994, when administered as aerosol. Finally, S18523 displays antiinflammatory properties, since it dose-dependently inhibits substance P-induced plasma extravasation both in the bladder (ID50 = 0.18 mg/kg i.v.) and bronchi (ID50 = 0.14 mg/kg i.v.) of the guinea-pig.

Potentiation by 2,2'-pyridylisatogen tosylate of ATP-responses at a recombinant P2Y1 purinoceptor

1. 2,2'-Pyridylisatogen tosylate (PIT) has been reported to be an irreversible antagonist of responses to adenosine 5'-triphosphate (ATP) at metabotropic purinoceptors (of the P2Y family) in some smooth muscles. When a recombinant P2Y1 purinoceptor (derived from chick brain) is expressed in Xenopus oocytes, ATP and 2-methylthioATP (2-MeSATP) evoke calcium-activated chloride currents (ICl,Ca) in a concentration-dependent manner. The effects of PIT on these agonist responses were examined at this cloned P2Y purinoceptor. 2. PIT (0.1-100 microM) failed to stimulate P2Y1 purinoceptors directly but, over a narrow concentration range (0.1-3 microM), caused a time-dependent potentiation (2-5 fold) of responses to ATP. The potentiation of ATP-responses by PIT was not caused by inhibition of oocyte ecto-ATPase. At high concentrations (3-100 microM), PIT irreversibly inhibited responses to ATP with a IC50 value of 13 +/- 9 microM (pKB = 4.88 +/- 0.22; n = 3). PIT failed to potentiate inward currents evoked by 2-MeSATP and only inhibited the responses to this agonist in an irreversible manner. 3. Known P2 purinoceptor antagonists were tested for their ability to potentiate ATP-responses at the chick P2Y1 purinoceptor. Suramin (IC50 = 230 +/- 80 nM; n = 5) and Reactive blue-2 (IC50 = 580 +/- 130 nM; n = 6) reversibly inhibited but did not potentiate ATP-responses. Coomassie brilliant blue-G (0.1-3 microM) potentiated ATP-responses in three experiments, while higher concentrations (3-100 microM) irreversibly inhibited ATP-responses. The results indicated that potentiation and receptor antagonism were dissociable and not a feature common to all known P2 purinoceptor antagonists. 4. In radioligand binding assays, PIT showed a low affinity (pKi < 5) for a range of membrane receptors, including: alpha 1, alpha 2-adrenoceptors, 5-HT1A, 5-HT1B, 5-HT2, 5-HT3, D1, D2, muscarinic, central benzodiazepine, H1, mu-opioid, dihydropyridine and batrachotoxin receptors. PIT showed some affinity (pKi = 5.3) for an adenosine (A1) receptor. 5. In guinea-pig isolated taenia caeci, PIT (12.5-50 microM) irreversibly antagonized relaxations to ATP (3-1000 microM); PIT also directly relaxed the smooth muscle and histamine was used to restore tone. Relaxations to nicotine (10-100 microM), evoked by stimulating intrinsic NANC nerves of taenia caeci preparations in the presence of hyoscine (0.3 microM) and guanethidine (17 microM), were not affected by PIT (50 microM, for 25-60 min). 6. These experiments indicate that PIT causes an irreversible antagonism of ATP receptors but, for recombinant chick P2Y1 purinoceptors, this effect is preceded by potentiation of ATP agonism. The initial potentiation by PIT (and by Coomassie brilliant blue-G) of ATP-responses raises the possibility of designing a new class of modulatory drugs to enhance purinergic transmission at metabotropic purinoceptors.