Effects of Ca Antagonists on the Norepinephrine Release and Contractile Responses of Isolated Canine Saphenous Veins to High KCl

摘要: Effects of verapamil, diltiazem and nicardipine on tritium overflow contraction evoked by 40 mM KCl were evaluated using canine saphenous vein strips preloaded with [3H]norepinephrine. Phentolamine, 10(-6) M, almost completely inhibited the induced KCl, while it significantly enhanced overflow. These responses to dependent external Ca2+. All Ca antagonists tested increased spontaneous in a concentration-dependent manner without any changes basal tension. Verapamil at M no significant effect overflow; concentrations above 10(-5) much more strongly than Diltiazem 3 X both KCl. A correlation between inhibitions three was observed, although y-intercept slope regression line for verapamil obtained plotting inhibition KCl-evoked as function greater those other two antagonists. The inhibitory effects not related their local anesthetic activities. Neither increase nor its phosphodiesterase inhibiting activity. results suggest that may inhibit mainly Ca2+-dependent transmitter release from nerve endings, acting postsynaptic sites relatively higher used, further release.