title: Involvement of calcium-activated potassium channels in the inhibitory prejunctional effect of morphine on peripheral sensory nerves.
abstract: We examined the contribution of potassium channels to the inhibitory effect of morphine on the increase in substance P release and cutaneous blood flow evoked by antidromic stimulation of the sectioned sciatic nerve. Cutaneous blood flow in the instep of the rat hind paw was measured by the non-invasive technique of laser Doppler flowmetry. Antidromic stimulation of the sectioned sciatic nerve caused a biphasic flow response, an initial transient decrease followed by an increase and an increase in substance P release into the subcutaneous perfusate of the instep of the rat hind paw. Both the increases of substance P release and cutaneous blood flow evoked by antidromic stimulation of the sectioned sciatic nerve were significantly inhibited by intra-arterial (i.a.) infusion of morphine (30 mumol/kg). This inhibitory effect of morphine was antagonized by pretreatment with naloxone (2 mg/kg, i.p.) or potassium channels blockers such as tetraethylammonium (40 mg/kg, i.v.). apamin (0.5 mg/kg, i.v.) and charybdotoxin (0.12 mg/kg. i.v.) but not with cesium chloride (85 mg/kg, i.v.) and glibenclamide (25 mg/kg, i.v.). These results suggest that the calcium-activated potassium channels may be involved in the prejunctional inhibitory effects of morphine in the hind instep of rats.
authors.affiliation: Department of Pharmacology, Osaka University Faculty of Dentistry, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Yonehara
authors.forename: S
authors.initials: S
authors.lastname: Takiuchi
mesh_terms: D000818:Animals; D001030:Apamin / Q000008:administration & dosage / Q000494:pharmacology; D018999:Charybdotoxin / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism; D009475:Neurons, Afferent / Q000187:drug effects*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D012867:Skin / Q000098:blood supply; D013373:Substance P / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D009294:Narcotics; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D001030:Apamin; D013373:Substance P; D019789:Tetraethylammonium; D009020:Morphine