1 The effects of the P2-purinoceptor agonists, adenosine 5'-triphosphate (ATP), a,fl-methylene ATP (a,f,-MeATP), fl,y-methylene ATP (fi,y-MeATP), L-fi,y-methylene ATP (L-fi,y-MeATP), adenosine-5'-O-(2-thiodiphosphate) (ADPfS), and 2-methylthio ATP (2-MeSATP) were investigated on the isometric tension of the rat anococcygeus muscle.2 Non-cumulative additions of ATP (100-1500MM), a,f,-MeATP (1-300yM), 13,'y-MeATP (10-300 pM), L-fy-MeATP (3-100 pM) and ADPfS (1-100 gM) produced concentration-dependent contractions, whereas 2-MeSATP (1-100pM) had no effect. The rank order of potency was a,,f- 6 The findings suggest that in the rat anococcygeus, smooth muscle cells are endowed with two distinct P2-purinoceptors which subserve contractions: a P2x-purinoceptor activated by ATP and its analogues, and another type of P2-purinoceptor activated by ADPfiS.

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