Heterogeneous effects of Ca2+ entry blockers on biphasic constriction of the rabbit ear artery

In the rabbit ear artery, nifedipine, verapamil, diltiazem and bepridil were found to be more potent in inhibiting the tonic than the phasic response to norepinephrine, while KB-944 and W-7 blocked these two responses equally. Since in the ear artery norepinephrine utilizes intracellular and extracellular Ca2+ for its phasic and tonic responses, respectively, the non-selective inhibitory effect of KB-944 suggests that Ca2+ entry blockade may not account solely for its vasodilator effect.