IDENTIFICATION OF ADENOSINE RECEPTORS IN HUMAN SPERMATOZOA

1. The effects of adenosine receptor agonists and antagonists on human sperm motility have been studied. Specific binding sites for adenosin e and its analogues on human sperm were also investigated. 2. Agonists stimulated human sperm motility in a dose-dependent manner with a pot ency order of 5'-N-ethylcarboxamidoadenosine (NECA, EC50 = 0.3 mumol/L ) >2-[p-(carboxyethyl) phenylethylamino]-5'-N-ethylcarboxamidoadenosin e (CGS-21680, EC50 = 10 mumol/L) > adenosine (EC50 = 100 mumol/ L). 3. NECA-stimulated motility was competitively inhibited by various adeno sine receptor antagonists. The potency order was 3,7-dimethy-1-proparg ylxanthine>8-(p-sulfophenyl) theophylline>xanthine amino congener. 4. The radioligand [H-3]-NECA bound to sperm membrane in a saturable mann er with a B(max) of 21.3 pmol/mg protein and equilibrium K(d) of 4 mum ol/L. Adenosine agonists and antagonists competed for [H-3]-NECA bindi ng with the same rank order of potency as for the stimulation of human sperm motility. 5. GTP-gammas inhibited 63% of specific [H-3]-NECA bi nding with IC50 value of 11 nmol/L. This suggests that the [H-3]-NECA binding sites may be coupled to one or more G proteins. 6. These resul ts indicate the presence of adenosine A2 receptors on human sperm whic h are responsible for adenosine-mediated enhancement of sperm motility .