A purinergic component of the excitatory postsynaptic current mediated by P2X receptors in the CA1 neurons of the rat hippocampus

The pyramidal neurons in the CA1 area of hippocampal slices from 17- to Ig- day-old rats have been investigated by means of patch clamp. Excitatory pos tsynaptic currents (EPSCs) were elicited by stimulating the Schaffer collat eral at a frequency below 0.2 Hz. It was found that inhibition of glutamate rgic transmission by 20 mu M 6-cyan0-7-nitroquinoxaline-2,3-dione (CNQX) an d 100 mu M 2-amino-5-phosphonovaleric acid (D-APV) left a small component o f the EPSC uninhibited. The amplitude of this residual EPSC (rEPSC) compris ed 25 +/- 11% of the total EPSC when measured at a holding potential of -50 mV. The rEPSC was blocked by selective P2 blocker pyridoxal phosphate-6-az ophenyl-2'-4'-disulphonic acid (PPADS) 10 mu M and bath incubation with non hydrolysable ATP analogues, ATP-gamma-S and alpha,beta-methylene-ATP at 50 and 20 mu M, respectively. The rEPSC was dramatically potentiated by extern al Zn2+ (10 mu M). In another series of experiments exogenous ATP was appli ed to the CA1 neurons in situ. An inward current evoked by ATP was inhibite d by PPADS to the same extent as the rEPSC. It is concluded that, depending on membrane voltage, about one-fifth to one-quarter of the EPSC generated by the excitatory synaptic input to the hippocampal CA1 neurons of rat is d ue to the activity of P2X receptors.