Adenosine activates the potassium channel via a P2 purinoceptor but not via an adenosine receptor in cultured rat superior colliculus neurons.

The effect of adenosine on superior colliculus neurons was examined by whole-cell patch clamp recording. Adenosine elicited whole-cell potassium currents. A selective A1 or A2a adenosine receptor agonist induced no current and furthermore, adenosine-evoked currents were not inhibited by selective A1 or A2a adenosine receptor antagonists or a non-selective adenosine receptor (P1 purinoceptor) antagonist, indicating that the currents are not mediated by adenosine receptors. In contrast, P2 purinoceptor agonists, such as 2-methylthio ATP (2-MeSATP), ATP, ADP, and AMP, produced similar potassium currents, whereas alpha,beta-methylene ATP, beta,gamma-metylene ATP, or UTP had no response. The order of their potencies for the current amplitudes was 2-MeSATP > ADP > adenosine > ATP >> AMP and this order corresponds to that for the P2Y purinoceptor. These results, thus, suggest that adenosine exerts an inhibitory effect at the postsynaptic site by activating the potassium channel via a P2Y purinoceptor in superior colliculus neurons.