Contractile Responses of Isolated Canine Blood Vessels to ATP and ADP

Abstract

Effects of ATP and ADP on helically cut strips of canine different blood vessels were studied, in comparison with those of K+ and norepinephrine (NE). ATP and ADP were equally effective in causing transient contractions in contrast to sustained contractions induced by K+ and NE. The mesenteric, renal arteries and portal veins were sensitive to both nucleotides. The response to the nucleotides and K+ was more dependent on Ca++ and Mg++ concentrations in bathing media than that to NE. Treatment of the strips with EGTA [ethylene glycol bis (.beta.-aminoethyl ether N,N,N'',N'' tetraacetic acid] in Ca++-free media quickly abolished the contractile responses to ATP, ADP and K+. Application of 0.1 mM Cd++ attenuated the contractile responses to K+ more markedly than those to NE, but did not affect ATP action. Verapamil at 0.5 .mu.M inhibited the K+-induced contraction alone, and 2 mM procaine inhibited the response to NE alone, but rather intensified the ATP-induced contraction. ATP and ADP produce a transient contraction of isolated canine blood vessels by a mechanism relating to an increased mobilization of loosely bound Ca++ in cell membranes.