Stimulation by N6-cyclopentyladenosine of A1 adenosine receptors, coupled to Gαi2 protein subunit, has a capacitative effect on human spermatozoa

The effects of selective A(t) receptor agonist on human spermatozoa were examined to verify physiological responses and to investigate the signal transduction pathway. N-6-Cyclopentyladenosine on uncapacitated spermatozoa did not induce spontaneous acrosome reaction after 5 h capacitation, whereas the number of capacitated spermatozoa, assessed by lysophosphatidylcholine-induced acrosome reaction with Pisum sativum agglutinin staining, was significantly increased. N-6-Cyclopentyladenosine was also added to capacitated human spermatozoa to find out whether the agonist could induce the acrosome reaction. Results, although statistically significant, could not be considered biologically significant. A(1)-Mediated capacitation was followed by the increase of tyrosine phosphorylation of a protein subset ranging between M-r = 200 000 and 30 000, Stimulation of A(1) receptor with the selective agonist elicited an agonist-induced inositol phospholipid hydrolysis leading to a transient rise of inositol triphosphate (IP3). This increase was not induced by A(1) receptor antagonist and was blocked by phospholipase C inhibitor. Coimmunoprecipitation experiments showed that the A(1) receptor is coupled to G alpha (i2) subunit suggesting that the activation of phospholipase C is mediated by beta gamma subunits. In conclusion, the A(1) adenosine receptor in human spermatozoa is coupled to G alpha (i2), signals via IP3, and affects the capacitative status of ejaculated spermatozoa.