Contractile responses and calcium movements induced by alpha 1-adrenoceptor stimulant, norepinephrine, in rabbit iris dilator muscle.
1. The mechanisms involved in contraction of rabbit iris dilator muscle induced by norepinephrine (NE) were studied. 2. The concentration-response curve of NE was not influenced by Ca2+ blockers in the normal physiological saline solution (PSS) and removal of Ca2+ from PSS. 3. In 0.01 mM EGTA containing Ca(2+)-free PSS, the NE-induced contraction was phasic, which was suppressed by TMB-8, cyclopiazonic acid, ionomycin and A23187 but still partly remained. 4. In 2 mM EGTA containing Ca(2+)-free PSS, NE increased the intracellular Ca2+ ([Ca2+]i) and muscle tension. Ryanodine abolished the increase in [Ca2+]i induced by NE but slightly inhibited the tension. 5. These results suggest that the NE-induced contraction of rabbit iris dilator in normal PSS is mainly due to the increase in the release of intracellularly sequestered Ca2+ and partly due to the Ca(2+)-independent processes.
Kokubu
N
N
Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Satoh
M
M
Takayanagi
I
I
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D016257:Fura-2; D066298:In Vitro Techniques; D007498:Iris / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011817:Rabbits; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects*; D012433:Ryanodine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D018340:Receptors, Adrenergic, alpha-1; D012433:Ryanodine; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine