Clonidine-induced rhythmic activity in rabbit anococcygeus muscle.
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.
Radjaee-Behbahani
N
N
Department of Physiology, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran.
Dehpour
A R
AR
Tajkhorshid
E
E
Kheirollahi
K
K
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
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