P-2-PURINOCEPTOR ANTAGONISTS .2. BLOCKADE OF P-2-PURINOCEPTOR SUBTYPES AND ECTO-NUCLEOTIDASES BY COMPOUNDS RELATED TO EVANS BLUE AND TRYPANBLUE

Effects of Evans blue and four derivatives as well as of trypan blue a nd four derivatives, mostly smaller fragments but two compounds with a n additional ethylene bridge in the center of the molecule, were studi ed on contractions of the rat vas deferens elicited by alpha,beta-meth ylene ATP (alpha,beta-MeATP; mediated by P-2X-purinoceptors), relaxati ons of the carbachol-precontracted guinea-pig taenia coli elicited by adenosine 5'-O-(2-thiodiphosphate) (ADP beta S; mediated by P-2Y-purin oceptors), and the degradation of ATP by rat vas deferens tissue. All compounds shifted the concentration-response curve of alpha,beta-MeATP in the rat vas deferens to the right, and most compounds increased th e maximum of the curve. Each member of the Evans blue series was simil ar in potency to the corresponding member of the trypan blue series. W here three concentrations were tested, the Arunlakshana-Schild regress ion was linear, and the slope did not differ from 1. The apparent K-d values were between 0.8 and 385 mu M. In the guinea-pig taenia coli, o nly the members of the trypan blue group were relatively potent, shift ing the concentration-response curve of ADP beta S to the right in a s urmountable manner. In 2 of 3 cases where three concentrations were te sted, the slope of the Arunlakshana-Schild regression was lower than 1 . Apparent K-d values in the trypan blue group were between 5.2 and 32 4 mu M. The removal of ATP from the medium by vas deferens tissue was decreased mainly by the members of the Evans blue group, with IC25% va lues between 13 and 158 (in 1 case > 1000) mu M. The results indicate that the position of the sulphonate residues at the terminal naphthale ne rings of these compounds hardly influences P-2X purinoceptor affini ty but greatly influences P-2Y affinity and ecto-nucleotidase blockade . Among active compounds, apparent purinoceptor affinity and ecto-nucl eotidase blockade increase with the size of the molecules up to Evans blue and trypan blue themselves; introduction of a central ethylene br idge does not result in a further gain in potency. NH01, the desmethyl derivative of Evans blue, seems to be interesting because it is the c ompound with the highest P-2X- versus P-2Y-selectivity presently avail able.