Effect of extracellular calcium on vascular contraction induced by phorbol ester.
In rat thoracic aorta, 12-0-tetradecanoyl-phorbol-13-acetate (TPA) caused a slowly onset, sustained vascular contraction. The contraction was markedly reduced in the absence of extracellular Ca2+, although small tension development was still observed. The tension developed by TPA in the presence of Ca2+ was decreased by serial addition of a Ca2+-channel blocker, verapamil in a concentration-dependent manner. TPA could cause vascular contraction to almost maximum level at lower concentration of extracellular Ca2+, compared with KCl- or norepinephrine-induced contraction. These results suggest that extracellular Ca2+ which influxes through Ca2+-channels into cytoplasm is necessary for full tension development by TPA, and that TPA increases sensitivity of contractile mechanisms coupling with Ca2+.
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011921:Rats, Inbred WKY; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
D011189:Potassium Chloride; D014700:Verapamil; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D009638:Norepinephrine