Effect of calcium-entry blockers and divalent cations on noradrenaline-induced contractions of the rat anococcygeus muscle.
The effect of three calcium-entry blockers and two divalent cations known to inhibit Ca++ entry on noradrenaline (NA)--and potassium (K+)--induced contractions were studied. The organic calcium entry-blockers--diltiazem (2.5 X 10(-7)-2.5 X 10(-6) M), nifedipine (2.8 X 10(-7)-2.8 X 10(-6) M) and flunarizine (2.5 X 10(-7)-2.5 X 10(-6) M) did not significantly (P greater than 0.05) reduce NA (3.75 X 10(-7)-1.2 X 10(-5) M) contractions. However, these concentrations of the calcium entry-blockers significantly (P less than 0.05) reduced K+ (80 mM)-induced contractions of the anococcygeus muscle. Both NA- and K+-induced contractions of the anococcygeus muscle were concentration--dependently reduced by the divalent cations manganese (10(-4)-10(-3) M) and cobalt (10(-4)-10(-3) M). It is suggested that while NA-induced contractions are dependent on extracellular calcium, it is quite possible that the agonist NA and K+ activate different Ca++ channels or that the mechanism of activation of the Ca++ channels is different.
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002412:Cations / Q000494:pharmacology; D002936:Cinnarizine / Q000031:analogs & derivatives / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D005444:Flunarizine; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012445:Sacrococcygeal Region
D002121:Calcium Channel Blockers; D002412:Cations; D002936:Cinnarizine; D003035:Cobalt; D008345:Manganese; D004110:Diltiazem; D009543:Nifedipine; D005444:Flunarizine; D011188:Potassium; D009638:Norepinephrine