Cytochalasin-B and phloretin depress contraction and relaxation of aortic smooth muscle.
Cytochalasin-B (20 microM) and phloretin (100 microM) blocked by more than 80% the contractile responses to calcium ions in partially depolarized rabbit aortic strips. Both also blocked, but only by approximately 50%, the responses to noradrenaline and histamine in normal calcium medium. The responses to these agonists in calcium-free EGTA medium were also blocked partially. Cytochalasin-B partially blocked the acetylcholine-induced relaxation of aortic strips precontracted with phenylephrine but not the relaxation due to nitroglycerine or compound A 23187. The relaxation due to isoprenaline was potentiated by cytochalasin B. Since both compounds are known to block hexose transport but share no other known effects, it is suggested that a glycolytic intermediate could be required for the contraction in response to calcium. However, the concentrations of cytochalasin-B required for these effects were somewhat greater than those usually required to block hexose transport.
Department of Pharmacology, Dalhousie University, Halifax, Canada.
P E
PE
Dresel
L
L
Knickle
D000109:Acetylcholine / Q000037:antagonists & inhibitors; D000818:Animals; D001011:Aorta / Q000187:drug effects; D002121:Calcium Channel Blockers; D003571:Cytochalasin B / Q000494:pharmacology*; D005260:Female; D006633:Histamine Antagonists; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D010656:Phenylephrine / Q000037:antagonists & inhibitors; D010693:Phloretin / Q000494:pharmacology*; D011817:Rabbits
D002121:Calcium Channel Blockers; D006633:Histamine Antagonists; D010656:Phenylephrine; D003571:Cytochalasin B; D000109:Acetylcholine; D010693:Phloretin; D009638:Norepinephrine