Diltiazem and verapamil inhibit norepinephrine-stimulated 45Ca uptake in rabbit aorta

The effects of two Ca antagonists, diltiazem (DZ) and verapamil (VP), on norepinephrine (NE)-stimulated 45Ca uptake in vascular smooth muscle from New Zealand White rabbit aortas were studied. Data were collected before, at 10, 30, and 60 min after drug addition, and during a simultaneous control period without drug addition. NE alone (6 X 10(-6) M) significantly increased 45Ca uptake from the extracellular space presumably by activating the receptor-operated Ca channel during excitation-contraction coupling. This effect was maximal by 10 min after NE addition and stable through the 60-min time point. Both VP (5 X 10(-5) M) and DZ (2.2 X 10(-7) M) inhibited the NE-stimulated 45Ca uptake at the 10- and 60-min time points, respectively. These data demonstrate that both DZ and VP inhibit 45Ca uptake from the extracellular space during activation of the receptor-operated Ca channel with NE. The effects of DZ and VP to inhibit NE-stimulated 45Ca uptake are demonstrated at concentrations which have been previously shown to cause dilation of vascular smooth muscle.