Adenosine A1receptors in cultured cerebellar granule cells: Role of endogenous adenosine

Adenosine A1receptors as well as other components of the adenylate cyclase system have been studied in cultured cerebellar granule cells. No significant changes in adenosine A1receptor number, assayed by radioligand binding in intact cells, were detected from 2 days in vitro (DIV) until 7 DIV. Nevertheless, a decline in this parameter was detected at 9 DIV. The steady-state levels of α-G(s) and α-G(i), detected by immunoblotting, showed similar profiles, increasing from 2 to 5 DIV and decreasing afterward. Forskolin-stimulated adenylate cyclase levels also showed an increase until 5 DIV, decreasing at 7 and 9 DIV. The adenosine A1receptor analogue cyclopentyladenosine (CPA) was able to inhibit cyclic AMP accumulation at 2, 5, and 7 DIV but failed to do so at 9 DIV. This inhibition was prevented by the specific adenosine A1receptor antagonist 8-cyclopentyl-1,3- dipropylxanthine. The presence of adenosine deaminase in the culture increased adenosine A1receptor number during the period studied and induced recovery of the inhibitory effect of CPA, lost after 7 DIV. These data suggest that functional expression of adenosine A1receptors and the other components of the adenylate cyclase system is subjected to regulation during the maturation of cultured cerebellar granule cells and demonstrates a key role for endogenous adenosine in the process.