ATP responses in the embryo chick ciliary ganglion cells

The ATP responses in ciliary neurons acutely dissociated from chick ciliary ganglia were investigated using the nystatin perforated patch recording mode. ATP induced a transient inward current at a holding potential of -50 mV in a concentration-dependent manner. The half-maximum effective concentration of ATP was 8.2 μM and the Hill coefficient was 0.9. The current-voltage relationship of the ATP response revealed a strong inward rectification at potentials more positive than -30 mV and the reversal potential was near 0 mV. The relative potencies of purinoceptor agonists were in the order of ATP > 2-methylthio-ATP > ADP. Neither adenosine, AMP nor α,β-methylene-ATP induced any response. The ATP-induced inward current was blocked by suramin, a selective P₂ purinoceptor antagonist, in a concentration-dependent manner. The half-maximum inhibitory concentration was 4.5 μM. The cytosolic Ca²⁺ concentration was increased by ATP and suramin inhibited the increase in a concentration-dependent manner. These results suggest that ATP operates non-selective cation channels by acting on P_2y purinoceptors and has a role in the excitation of ciliary neurons.