Effects of suramin on hippocampal apyrase activity and inhibitory avoidance learning of rats

The action of suramin on apyrase activity in hippocampal synaptosomes and i ts effects on retention of inhibitory avoidance learning were evaluated. Su ramin, a P-2-purinoceptor antagonist, significantly inhibited in a noncompe titive manner the ATP and ADP hydrolysis promoted by apyrase in hippocampal synaptosomes of adult rats. The Ki values obtained were 72.8 and 109 mu M for ATP and ADP hydrolysis, respectively. Intrahippocampal infusion of sura min (0.01, 0.1, 1, and 10 mu g) immediately posttraining, in a dose-depende nt effect, significantly reduced the response latency during the retention test applied 24 h after the rats received step-down inhibitory avoidance tr aining. The amnesic effects promoted by suramin probably occur by its antag onist action on hippocampal P-2-purinoceptors and NMDA receptors. In view o f the fact that ATP-metabolizing enzymes and P-2-purinoceptors have similar binding domains, these results suggest that suramin can either alter ATP d egradation and/or block purinergic neurotransmission. (C) 1999 Elsevier Sci ence Inc.