Distribution patterns of different P2x receptor phenotypes in acutely dissociated dorsal root ganglion neurons of adult rats

P2x receptors may be used to detect ATP release from tissues during physiol ogical and pathological conditions. We used whole-cell patch clamp recordin gs to study the expression of P2x receptor phenotypes, their distribution p atterns, and their sensitivity to alpha beta mATP and suramin in dorsal roo t ganglion (DRG) neurons acutely dissociated from adult rats. Based on the onset and decay rates of 10 mu M ATP-evoked currents, we showed three types of P2x currents: fast, slow, and mixed. Each of these P2x receptor phenoty pes had a distinct distribution pattern among DRG neurons. The fast P2x cur rents were predominantly expressed in small-diameter, isolectin-B4 (IB4)-po sitive, and capsaicin-sensitive DRG neurons. The slow P2x currents were exp ressed in both small and medium DRG neurons, and about half of them were IB 4 positive. The mixed P2x currents were also expressed in both small and me dium-sized DRG neurons, and most of these neurons were IB4-positive neurons . The slow and mixed P2x current groups had both capsaicin-sensitive and -i nsensitive DRG neurons. All phenotypes revealed with 10 mu M ATP could be i nhibited by 30 mu M suramin. All DRG neurons with fast or mixed P2x current s were also sensitive to 10 mu M alpha beta mATP, and alpha beta mATP evoke d currents similar to those induced by ATP. The group expressing slow P2x c urrents could be further divided into alpha beta mATP-sensitive and -insens itive groups. Thus, the relationships among P2x receptor phenotypes, cell s izes, IB4 positivity, and capsaicin sensitivity are more complicated than p reviously thought, and different P2x receptors may be involved in both noci ceptive and non-nociceptive functions.