FUNCTIONAL EXPRESSION OF P-2U RECEPTORS IN RAT SPERMATOGENIC CELLS - DUAL MODULATION OF A CA2-ACTIVATED K+ CHANNEL()

Previous study has demonstrated functional expression of a sperm Ca2+- activated K+ channel in Xenopus oocytes injected with RNAs from the ra t testes. Using the same expression system, the present study investig ated the specific purinoceptor subtype involved in mediating the effec t of extracellular ATP. The effect of ATP on an outwardly rectifying c urrent, previously demonstrated to be mediated by a ''Maxi'' Ca2+-acti vated K+ channel, was compared to the current responses to different n ucleotides using the two-electrode voltage-clamp technique. An order o f relative effectiveness appeared to be UTP > ATP > ADP > adenosine, c onsistent with the pharmacological classification of P-2U receptors. A TP was also found to exert an inhibitory effect on the Ca2+-activated K+ current, elicited by the Ca2+ ionophore ionomycin. A similar inhibi tory effect was observed with UTP, again suggesting the involvement of P-2U receptor. RT-PCR study also confirmed the expression of P-2U rec eptor mRNA in isolated spermatogenic cells. The present results demons trate the expression of P-2U receptor and its dual role, both stimulat ory and inhibitory, in the modulation of the Ca2+-activated K+ channel in spermatogenic cells. The present finding lends support to an impor tant role of extracellular ATP in sperm functions. (C) 1998 Academic P ress.