Nitroglycerin-Sensitive and -Resistant Contractions Mediated by Receptor-Operated Calcium Channels in Rabbit Ear Artery

Abstract

In isolated rabbit ear arteries incubated in a Ca²⁺-free medium with EGTA and nifedipine in the presence of norepinephrine, serotonin or histamine, an addition of Ca²⁺ induced a tonic contraction which is due to Ca²⁺ entry through receptor-operated Ca²⁺ channels (ROCs). Nitroglycerin (10^-4 M) significantly inhibited the ROCs-dependent contractions produced by serotonin or histamine, but failed to inhibit the ROCs-dependent contraction by norepinephrine. These results suggest the possible existence of two types of receptor-operated Ca²⁺ channels in rabbit ear artery.