The Journal of pharmacology and experimental therapeutics
-
J. Pharmacol. Exp. Ther. · Jul 2003
Amide local anesthetics potently inhibit the human tandem pore domain background K+ channel TASK-2 (KCNK5).
Blockade of voltage-gated sodium (Na+) channels by local anesthetics represents the main mechanism for inhibition of impulse propagation. Local anesthetic-induced potassium (K+) channel inhibition is also known to influence transmission of sensory impulses and to potentiate inhibition. K+ channels involved in this mechanism may belong to the emerging family of background tandem pore domain K+ channels (2P K+ channels). ⋯ Local anesthetics [300 micro M R-(+)-bupivacaine] caused significantly greater depolarization of the resting membrane potential of TASK-2-expressing oocytes compared with water-injected control oocytes (15.8 +/- 2.5 mV versus 0.1 +/- 0.05 mV; p < 0.001). Chimeric TASK-1/TASK-2 2P K+ channel subunits that retained pH sensitivity demonstrated that the carboxy domain of TASK-2 mediates the greater local anesthetic sensitivity of TASK-2. These results show that clinically achievable concentrations of local anesthetics inhibit background K+ channel function and may thereby enhance conduction blockade.
-
J. Pharmacol. Exp. Ther. · Jul 2003
5-Hydroxytryptamine (5-HT)2 receptor involvement in acute 5-HT-evoked scratching but not in allergic pruritus induced by dinitrofluorobenzene in rats.
We investigated the role of serotonin (5-hydroxytryptamine; 5-HT)2 and 5-HT3 receptor subtypes in acute itch-associated scratching behavior as well as in an allergic pruritus model in rats. Intradermal 5-HT evoked hind limb scratching directed toward the injection site in naïve rats. Scratching behavior was significantly reduced by pretreatment with the 5-HT2 receptor antagonist ketanserin. ⋯ To produce a model of allergic pruritus, skin was sensitized by topical application of 5% dinitrofluorobenzene (DNFB). One month later, repeated challenge of the skin with 0.2% DNFB at weekly intervals elicited scratching as part of the immediate allergic response. Scratching was not affected by ketanserin or by the 5-HT3 receptor antagonist ondansetron, indicating that neither 5-HT2 nor 5-HT3 receptors is involved in itch-associated scratching behavior caused by allergic skin dermatitis in rats.
-
J. Pharmacol. Exp. Ther. · Jul 2003
N-(4-Tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropyrazine -1(2H)-carbox-amide (BCTC), a novel, orally effective vanilloid receptor 1 antagonist with analgesic properties: II. in vivo characterization in rat models of inflammatory and neuropathic pain.
The vanilloid receptor 1 (VR1) is a cation channel expressed predominantly by nociceptive sensory neurons and is activated by a wide array of pain-producing stimuli, including capsaicin, noxious heat, and low pH. Although the behavioral effects of injected capsaicin and the VR1 antagonist capsazepine have indicated a potential role for VR1 in the generation and maintenance of persistent pain states, species differences in the molecular pharmacology of VR1 and a limited number of selective ligands have made VR1 difficult to study in vivo. N-(4-Tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropryazine-1(2H)-carbox-amide (BCTC) is a recently described inhibitor of capsaicin- and acid-mediated currents at rat VR1. ⋯ BCTC also reduced mechanical hyperalgesia and tactile allodynia 2 weeks after partial sciatic nerve injury (10 and 30 mg/kg p.o.). BCTC did not affect motor performance on the rotarod after administration of doses up to 50 mg/kg p.o. These data suggest a role for VR1 in persistent and chronic pain arising from inflammation or nerve injury.
-
J. Pharmacol. Exp. Ther. · Jul 2003
SSR591813, a novel selective and partial alpha4beta2 nicotinic receptor agonist with potential as an aid to smoking cessation.
(5aS,8S,10aR)-5a,6,9,10-Tetrahydro,7H,11H-8,10a-methanopyrido[2',3':5,6]pyrano[2,3-d]azepine (SSR591813) is a novel compound that binds with high affinity to the rat and human alpha4beta2 nicotinic acetylcholine receptor (nAChR) subtypes (Ki = 107 and 36 nM, respectively) and displays selectivity for the alpha4beta2 nAChR (Ki, human alpha3beta4 > 1000, alpha3beta2 = 116; alpha1beta1deltagamma > 6000 nM and rat alpha7 > 6000 nM). Electrophysiological experiments indicate that SSR591813 is a partial agonist at the human alpha4beta2 nAChR subtype (EC50 = 1.3 micro M, IA =19% compared with the full agonist 1,1-dimethyl-4-phenyl-piperazinium). In vivo findings from microdialysis and drug discrimination studies confirm the partial intrinsic activity of SSR591813. ⋯ The compound (10 mg/kg i.p.) also prevents withdrawal signs precipitated by mecamylamine in nicotine-dependent rats and partially blocks the discriminative cue of an acute precipitated withdrawal. SSR591813 (20 mg/kg i.p.) reduces i.v. nicotine self-administration and antagonizes nicotine-induced behavioral sensitization in rats. The present results confirm important role for alpha4beta2 nAChRs in mediating nicotine dependence and suggest that SSR591813, a partial agonist at this particular nAChR subtype, may have therapeutic potential in the clinical management of smoking cessation.
-
J. Pharmacol. Exp. Ther. · May 2003
In vivo pain-inhibitory role of nociceptin/orphanin FQ in spinal cord.
Because nociceptin/orphanin FQ (N/OFQ) has both pronociceptive (hyperalgesia) and antinociceptive actions in pharmacological experiments, and there is no significant difference in the nociceptive responses between NOP(-/-) mice and their wild-type (NOP(+/+)) littermates, the physiological role of N/OFQ in pain regulation remains to be determined. Under the hypothesis that the use of molecularly distinct nociception test may reveal the pain modality-specific role of N/OFQ, we attempted to examine the physiological role of N/OFQ in pain transmission by using newly developed algogenic-induced nociceptive flexion test in NOP(-/-) and NOP(+/+) mice or NOP antagonist-treated mice. The nociceptive flexor responses upon intraplantar injection of bradykinin or substance P, which stimulates polymodal substance P-ergic fibers, were markedly potentiated in NOP(-/-) mice, compared with those in its NOP(+/+) mice. ⋯ On the other hand, there were no significant differences in NK1-like immunoreactivity, [(3)H]substance P binding, or NK1 gene expression in the dorsal horn of the spinal cord between NOP(-/-) and NOP(+/+) mice. In addition, NOP antagonists decreased the threshold in nociception tests driving spinal substance P neurotransmission. All these findings suggest that the N/OFQ-ergic neuron may play an in vivo inhibitory role on the second-order neurons for primary polymodal substance P-ergic fibers in the spinal cord.