EFFECTS OF α-ADRENOCEPTOR ANTAGONISTS AND α,β-METHYLENE ATP ON ELECTRICAL RESPONSES PRODUCED BY NEUROTRANSMITTERS IN SMOOTH MUSCLE CELLS OF THE RAT TAIL ARTERY

Abstract

Effects of α-adrenoceptor antagonists and α,β-methylene ATP (mATP) on electrical responses elicited by perivascular nerve stimulation were studied in smooth muscle cells of the rat tail artery, and the results were compared with those of exogenously applied noradrenaline (NA) or ATP. Nerve stimulation elicited an excitatory junction potential (e.j.p.) and slow depolarization. The latter component and NA-induced depolarization were blocked by α-adrenoceptor antagonists; prazosin and phentolamine were more potent than yohimbine. The membrane resistance was increased during the slow depolarization and the NA-induced depolarization. mATP depolarized the membrane, decreased the membrane resistance, reduced the time constant of the falling phase of the e.j.p., inhibited the amplitude of the e.j.p. and the ATP-induced depolarization to a similar extent, and enhanced amplitude of the slow depolarization and the NA-induced depolarization. The results provided evidence that in this artery, both α₁- and α₂-adrenoceptors are involved in the NA-induced depolarization. Inhibition by mATP of the e.j.p. cannot be concluded solely due to desensitization of the postjunctional ATP-receptor.