There is evidence indicating co-release of ATP and GABA neurotransmitters [1] and co-expression of P2X ATP-gated channels and GABA-gated channels, suggesting that these two structurally distinct channels may functionally communicate with each other. In this study, we expressed in rat P2X4 and rat rho1 subunits in human embryonic kidney 293 cells individually or in combination, and measured whole-cell agonist-evoked currents by patch-clamp technique at a holding potential of -60 mV in intracellular and extracellular solutions, both of which contained Na⁺ and Cl^– as the major ion species. In cells co-expressing P2X4 and rho1 subunits, the mean ± SEM amplitude of peak currents evoked by co-application of ATP (100 μM) and GABA (10 μM) was 3066 ± 324 pA (n = 5), which was significantly reduced compared with that predicted from the sum of currents evoked by ATP and GABA separately (4554 ± 587 pA; p 0.1, paired Student’s t test). Similarly in cells expressing rho1 subunit only, the currents elicited by co-application of GABA and ATP (2649 ± 274 pA; n = 4) were similar to those by GABA alone (2704 ± 294 pA; p > 0.1, paired Student’s t test). In addition, there were no observable alterations in activation and deactivation of P2X4 receptor by GABA and of GABA_c receptor by ATP. In summary, our results indicate functional cross-inhibition between P2X4 and GABAc receptors and exclude the possibility that such cross-inhibition is due to functional modulation of P2X4 receptors by GABA or of GABA_c receptor by ATP [2].