ON MODE OF ACTION OF DIPYRIDAMOLE - INHIBITION BY DIPYRIDAMOLE OF UPTAKE OF ADENOSINE IN ERYTHROCYTES

10-9-10-6 M Dipyridamole, which is used for coronary dilation' lowers the permeability of erythrocytes of guinea pigs to adenosine and inosine. For inhibition of the adenosine deaminase, however, concentrations of 10-4 M are necessary. There is a difference of 103-105 between the concentration of dipyridamole which inhibits the adenosine deaminase and the concentration which decreases the permeability of erythrocytes to adenosine or inosine. Therefore the inhibition of uptake into the cells should be more important for the pharmacological effects than the inhibition of the adenosine deaminase. The unchanged deamination of adenosine by a concentration of 10-6 M Di-pyridamole, which inhibits the uptake of adenosine into the cells completely, indicates, that adenosine is deaminated on the outer surface of the cell membrane. © 1969 Springer-Verlag.