HIGH EXPRESSION OF NITROBENZYLTHIOINOSINE-INSENSITIVE DIPYRIDAMOLE BINDING-SITES IN POSTMORTEM HUMAN EPENDYMAL TISSUE

The presence of both nitrobenzylthioinosine-sensitive and nitrobenzylt hioinosine-insensitive dipyridamole binding sites in postmortem human ependymal tissue is reported. Displacement studies using 15 nM [H-3]di pyridamole revealed 50-60% of the sites were sensitive to nitrobenzylt hioinosine. Non-linear analysis of binding isotherms to estimate the d ensity of nitrobenzylthioinosine-sensitive and -insensitive sites reve aled a maximum number of nitrobenzylthioinosine-sensitive binding site s (B-max) of 395 +/- 19 fmol/mg protein and a nitrobenzylthioinosine-i nsensitive B-max of 3910 +/- 700 fmol/mg protein (corresponding K-d va lues of 0.1 nM and 114 nM respectively). Thus there are approximately 10 times as many nitrobenzylthioinosine-insensitive sites as nitrobenz ylthioinosine-sensitive [H-3]dipyridamole binding sites in human epend ymal membranes.