Potentiating effect of Bay K 8644 on the noradrenaline-induced contraction in rabbit renal and femoral arteries.
1. In rabbit renal and femoral arteries, Bay K 8644 produced a contraction and nifedipine inhibited it. 2. Bay K 8644 potentiated the responses to noradrenaline (NA) and potassium (K+). In the presence of nifedipine, Bay K 8644 potentiated NA. 3. In a Ca2+-free medium with EGTA, NA produced a transient contraction which was not affected by Bay K 8644 or nifedipine. Bay K 8644 enhanced the Ca2+-induced contraction in a Ca2+-free medium containing EGTA, nifedipine and NA. 4. The combined treatment with nimodipine and nifedipine further inhibited the Bay K 8644 induced potentiation of Ca2+ responses in the presence of NA as compared to nifedipine alone. 5. In the presence of but not absence of Bay K 8644, Ca2+ caused contractions in a Ca2+-free medium containing EGTA, nifedipine and KCl. 6. Vanadate further enhanced the Bay K 8644 induced potentiation of the Ca2+ responses in the presence of K+ but not NA. 7. These results suggest that, in rabbit renal and femoral arteries, Bay K 8644 does not affect the intracellular translocation of Ca2+ but increases Ca2+-influx activated by K+ or NA. Bay K 8644-induced potentiation of NA responses is likely due to an increase in Ca2+-influx through voltage operated channels (VOC) activated by NA. Also, K+ activated VOC may be coupled to Ca2+-extrusion pumps more than NA activated VOC.
Hashimoto
M
M
Department of Pharmacology, School of Medicine, University of Hawaii, Honolulu 96822.
Satake
N
N
Ito
M
M
Masumura
S
S
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; D004357:Drug Synergism; D004533:Egtazic Acid / Q000494:pharmacology; D005263:Femoral Artery / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012077:Renal Artery / Q000187:drug effects; D014638:Vanadates / Q000494:pharmacology
D014638:Vanadates; D004533:Egtazic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D011188:Potassium; D009638:Norepinephrine