Characterization of three types of ATP-activated current in relation to P2X subunits in rat trigeminal ganglion neurons

In the present study, ATP-activated currents (IATPs) recorded from rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique are classified into three types (F, I and S) based on the characteristics of their activation and desensitization. The time of rising phase (R10–90) of types F, I and S of IATP is measured to be 33.6 ± 4.5, 62.2 ± 9.9 and 302.1 ± 62.0 ms respectively, and positively correlated to cell size. The time of decaying phases (D10–90) of types F and S is 399.4 ± 58.2 and > 1500 ms, respectively. The dose–response curves for the three types of IATP show that their EC50 values are close (3.44 × 10− 5, 4.89 × 10− 5 and 4.14 × 10− 5 M for types F, I and S respectively, P > 0.05). Their reversal potentials are basically the same, varying from + 4 to + 10 mV. In addition, using whole-cell patch clamp technique in combination with single cell immunohistochemical staining for P2X receptor subunits, our results suggest that the type distinction of ATP-activated current was associated with cell size and P2X receptor subunits: small-sized cells with type F of IATP express only P2X1 and/or P2X3 subunits, while cells with types S and I of IATP express P2X2 or P2X4 in addition to P2X1 and P2X3.