| Repairing and regeneration are very complex after nerve injury. Recent studies found that P2X receptor acts as an important role in the pathophysiology of peripheral nerve injury. Morphological changes of P2X receptor of DRG neurons have been studied recently after sciatic nerve injury in rats, but the results were not consistent because of different model, animal and standard. It has not been reported about electrophysiological changes of P2X receptor of DRG neurons after sciatic nerve injury in rats. In order to study the roles of P2X receptor of DRG neurons in the pathophysiology of peripheral nerve injury, the electrophysiological and immunoreactive changes of P2X receptor of rat DRG neurons were investigated using whole-cell patch clamp techniques and immunohistochemical staining after sciatic nerve injury at different times. The results were as follows:1. Morphology of DRG neurons with distinct soma diameter of 13~29μm, 30~40μm, 41~60μm and single or double dendrite were readily distinguished, and were not changed after sciatic nerve injury.2. Resting membrane potential of DRG neurons of control group, operation group (2d) and operation group (7d) were (-54.29±4.89) mV (n=38), (-53.72±4.95) mV (n=32) and (-56.70±5.43) mV (n=43); series resistance were (11.37±3.96) MΩ, (10.37±2.64) MΩ and (11.85±2.07) MΩ; membrane capacity were (12.63±2.27) pF, (11.45±2.98) pF and (13.05±2.54) pF, using whole-cell patch clamp, respectively. Passive membrane electrophysiological characters of DRG neurons were not markedly changed after sciatic nerve injury ( p>0.05).Action potential (AP) was recorded when DRG neurons were stimulated by a series of current from hyperpolarization to depolarization (-60pA～140pA, step=20pA, time=200ms). The threshold and time of AP were markedly changed after sciatic nerve injury at 7 days ( p<0.01). However, the threshold and time of AP were not markedly changed after sciatic nerve injury at 2 days ( p>0.05).3. Membrane potential of DRG neurons fluctuates spontaneously under current clamp. Membrane potential of neurons of control and operation (2d) group were under threshold potential, and all recorded neurons have not action potential. However, 11.63% (5/43) of neurons showed spontaneous action potential at membrane potential after sciatic nerve injury at 7 days.4. Rapid application of ATP to DRG neurons evoked action potential under current clamp. The response to ATP was blocked by suramin. Depolarization amplitudes of action potential of control group evoked by 0.1μM, 1μM, 10μM and 100μM ATP were 2.00mV, 13.14mV, 25.73 mV and 42.50mV respectively; and depolarization amplitudes of operation group (7d) were 4.00mV, 21.56mV, 31.00mV and 47.67mV respectively. It was significantly different from each group (p<0.01). Median effective concentration (EC50) of ATP of control and operation (7d) group were 4.26 ±0.69μM and 1.08±0.90μM respectively ( p<0.01).5. Rapid application of ATP to DRG neurons evoked a fast-activating inward current under voltage clamp holding DRG neurons potential about -60mV. Amplitudes of inward current of control group evoked by 0.1μM, 1μM, 10μM and 100μM ATP were 2.34pA, 5.00pA, 9.67pA and 29.10pA respectively; and amplitudes of inward current of operation group (7d) were 4.60pA, 9.00pA, 16.29pA and 34.55pA respectively. It was significantly different from each group (p<0.01). EC50 of ATP of control and operation (7d) group were 3.87±1.40μM and 1.15±0.86μM respectively ( p<0.01).In control and operation (7d) group, 30.43% (7/23) and 36.36% (8/22) of neurons tested responded to ATP with a transient current, and 52.17% (12/23) and 36.36% (8/22) of neurons with a sustained current, respectively. Percentage of transient current and sustained current were not markedly different after sciatic nerve injury ( p>0.05). 6. Immunohistochemistry showed that 31.73%, 35.26% and 42.93% of DRG neurons were P2X3 receptor-positive neurons in control, operation (2d) and operation (7d) group, respectively. It was significantly different from co...
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