title: Clonidine-induced rhythmic activity in rabbit anococcygeus muscle.
abstract: 1. Clonidine 0.5 mM induced an extremely regular rhythmic activity in isolated rabbit anococcygeus muscle. The movements were resistant to tetrodotoxin effect. 2. Prazosin (5 x 10(-8)M-5 x 10(-6)M) and yohimbine (1.5 x 10(-7)M-5 x 10(-4)M) showed no remarkable effect on clonidine-induced rhythmic activity. 3. The clonidine-induced contractions were dependent on extracellular calcium and could be inhibited by the omission of calcium from medium or the introduction of verapamil (IC50 = 1.3 x 10(-7)M) or nifedipine (IC50 = 7.5 x 10(-8)M). 4. Pretreatment of animals with reserpine made the preparations 2800-fold more sensitive to this action of clonidine. 5. It can be concluded from this study that clonidine is able to induce rhythmic activity in rabbit anococcygeus muscle through a mechanism that increases intracellular concentration of Ca++ via membrane calcium channels.
authors.affiliation: Department of Physiology, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: N
authors.initials: N
authors.lastname: Radjaee-Behbahani
authors.forename: A R
authors.initials: AR
authors.lastname: Dehpour
authors.forename: E
authors.initials: E
authors.lastname: Tajkhorshid
authors.forename: K
authors.initials: K
authors.lastname: Kheirollahi
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011817:Rabbits; D012110:Reserpine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D018759:Adrenergic Uptake Inhibitors; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D013779:Tetrodotoxin; D012110:Reserpine; D003000:Clonidine; D002118:Calcium