Heterogeneity of the functional expression of P2X3 and P2X2/3 receptors inthe primary nociceptive neurons of rat

The properties and functional expression of the purinergic receptors in sma ll (nociceptive) neurons acutely isolated from the DRG of rat were studied using whole-cell patch-clamp recording. The responses of small DRG neurons to ATP exhibited diverse kinetics and could be subdivided into three types: rapid, slow and mixed kinetics responses. Their affinities to agonists all owed to identify the responsible receptors as P2X3 ("fast") and heteromeric P2X2/3 ("slow") subtypes. The expression of different responses dramatical ly varied both on the neuron-to-neuron and animal-to-animal basis. Out of 7 44 neurons tested 24% of cells demonstrated predominance of functional P2X2 /3 receptors, 44% had mixed representation and in 32% of cells P2X3 recepto rs dominated. All the animals tested (110) could be subdivided into 3 group s: in 19% of animals the response of each cell to ATP was mediated by P2X2/ 3 receptors, both types of ATP-evoked currents were found in 58% of animals and only in 23% of the animals P2X3 receptors dominated. Our results argue with exclusive role of P2X3 receptors in purinergic signaling in primary n ociceptive neurons.