[The mode of action of ATP on the isolated internal carotid artery (author's transl)].

Adenosine triphosphate (ATP) has been known to induce vasodilation in various vascular beds. Recently, we reported that ATP produced vasoconstrictions in isolated internal and external carotid arteries of dogs. In the present study, the mode of the ATP-induced vasoconstriction in the internal carotid artery was analysed from the physiological and pharmacological points of view. The results obtained were as follows: 1) ATP (5 X 10(-6) approximately 2 X 10(-4) M) caused dose-dependent vasoconstrictions in the internal carotid artery. 2) The ATP-induced vasoconstriction was not affected by pretreatment with phenoxybenzamine, propranolol, atropine, cyproheptadine, or tetrodotoxin. 3) Verapamil suppressed dose-dependently the contractile response. 4) ATP caused no vasoconstriction in a calcium-free Krebs solution containing Im M EGTA. 5) ATP produced no further vasoconstriction in the preparation which had been in a state of contracture in a high potassium Krebs solution. These results suggest that an increase of potential-dependent Ca++ influx into the arterial smooth muscle cells may play a major role in the ATP-induced vasoconstriction.