Bay K 8644-induced potentiation of the contractile response of rabbit iliac artery to caffeine in a Ca2+-free medium.
1. In a Ca2+-free medium caffeine (10 mM) was still able to cause a phasic contraction in rabbit iliac arteries. 2. Bay K 8644 at 10(-6) but not at 10(-7) M potentiated the residual response to caffeine in a Ca2+-free medium. In a Ca2+-free medium with or without KCl (40 mM), Bay K 8644, however, caused no contraction. 3. Nifedipine (10(-6) M) did not affect the residual caffeine-response or the potentiating effect of Bay K 8644. Verapamil (10(-6) M), however, inhibited both the caffeine response and the potentiation. 4. Bay K 8644 (10(-6) M) potentiated the contractile response to Ca2+ (0.01-2.4 mM) in a Ca2+-free medium containing KCl. The potentiation was equally inhibited by nifedipine or verapamil. 5. La#+ (1 mM), EGTA (0.1 mM), or vanadate (10(-4) M) completely inhibited the Bay K 8644-induced potentiation without affecting the residual caffeine response. 6. These results suggest that the potentiating action of Bay K 8644 on the residual caffeine response in a Ca2+-deficient medium may not be related to voltage-dependent Ca2+ channels. In addition, the activity of Ca2+-ATPase in sarcolemmal membranes may be important in this potentiation.
Ito
M
M
Department of Pharmacology, School of Medicine, University of Hawaii, Honolulu 96822.
Satake
N
N
Morikawa
M
M
Shibata
S
S
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002122:Calcium Chloride / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007083:Iliac Artery / Q000187:drug effects; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D014638:Vanadates / Q000494:pharmacology
D002110:Caffeine; D014638:Vanadates; D004533:Egtazic Acid; D011189:Potassium Chloride; D007811:Lanthanum; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D002122:Calcium Chloride; D002118:Calcium