The effects of phorbol-12,13-dibuterate (PDBu) on total sodium current (INa-total), tet-rodotoxin-resistant sodium current (INa-TTXr), 4-AP-sensitive potassium current (IA) and TEA-sensitive potassium current (IK) in trigeminal ganglion (TG) neurons were investigated. Whole-cell patch clamp techniques were used to record ion currents in cultured TG neurons of rats. Results revealed that 0.5 μmol/L PDBu reduced the amplitude of INa-total by (38.3±4.5)% (n=6, P<0.05), but neither the G-V curve (control: V0.5 =-17.1±4.3 mV, k=7.4±1.3; PDBu: V0.5=-15.9±5.9 mV, k=5.9±1.4; n=6, P>0.05) nor the inactivation rate constant (control: 3.6±0.9 ms; PDBu: 3.6±0.8 ms; n=6, P>0.05) was altered. 0.5 μmol/L PDBu could significantly increase the amplitude of INa-TTXr by (37.2± 3.2)% (n=9, P<0.05) without affecting the G-V curve (control: V0.5=-14.7±6.0 mV, k=6.9± 1.4; PDBu: V0.5=-11.1±5.3 mV, k=8.1±1.5; n=5, P>0.05) or the inactivation rate constant (control: 4.6±0.6 ms; PDBu: 4.2±0.5 ms; n=5, P>0.05). 0.5 μmol/L PDBu inhibited IK by (15.6±5.0) % (n=16, P<0.05), and V0.5 was significantly altered from - 4.7±1.4 mV to -7.9 ±1.8 mV (n=16, P<0.05). IA was not significantly affected by PDBu, 0.5 μmol/L PDBu decreased IA by only (0.3±3.2)% (n=5, P>0.05). It was concluded that PDBu inhibited INa-total but enhanced INa-TTXr, and inhibited IK without affecting IA. These data suggested that the activation of PKC pathway could exert the actions.
This study investigated the modulatory effect of synthetic cannabinoids WIN55,212-2 on 5-HT3 receptor-activated currents (I5-HT3) in cultured rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique. The results showed that: (1) The majority of examined neurons (78.70%) were sensitive to 5-HT (3-300 μmol/L). 5-HT induced inward currents in a concentration-dependent manner and the currents were blocked by ICS 205-930 (1 μmol/L), a selective antagonist of the 5-HT3 receptor; (2) Pre-application of WIN55,212-2 (0.01-1 μmol/L) significantly inhibited I5-HT3 reversibly in concentration-dependent and voltage-independent manners. The concentra-tion-response curve of 5-HT3 receptor was shifted downward by WIN55,212-2 without any change of the threshold value. The EC50 values of two curves were very close (17.5±4.5) mmol/L vs. (15.2±4.5) mmol/L and WIN55,212-2 decreased the maximal amplitude of I5-HT3 by (48.65±4.15)%; (3) Neither AM281, a selective CB1 receptor antagonist, nor AM630, a selective CB2 receptor antagonist re-versed the inhibition of I5-HT3 by WIN55,212-2; (4) When WIN55,212-2 was given from 15 to 120 s before 5-HT application, inhibitory effect was gradually increased and the maximal inhibition took place at 90 s, and the inhibition remained at the same level after 90 s. We are led to concluded that-WIN55,212-2 inhibited I5-HT3 significantly and neither CB1 receptor antagonist nor CB2 receptor an-tagonist could reverse the inhibition of I5-HT3 by WIN55,212-2. Moreover, WIN55,212-2 is not an open channel blocker (OCB) of 5-HT3 receptor. WIN55,212-2 significantly inhibited 5-HT-activated currents in a non-competitive manner. The inhibition of I5-HT3 by WIN55,212-2 is probably new one of peripheral analgesic mechanisms of WIN55,212-2, but the mechanism by which WIN55,212-2 in-hibits I5-HT3 warrants further investigation.
The different effects of capsaicin on I_ A and I_ K currents in pain-conduct neurons of trigeminal ganglia (TG) were investigated. In cultured TG neurons of rats, whole-cell patch clamp techniques were used to record the I_ A and I_ K before and after capsaicin perfused. Results revealed that 1 μmol/L capsaicin could inhibit the amplitude of I_ A by 48.2 % (n=10, P<0.05), but had no inhibitory effect on I_ K (n=7, P>0.05). Ten μmol/L capsaicin could significantly inhibit the amplitude of I_ A by 93.2 % (n=8, P<0.01), but only slightly inhibit the amplitude of I_ K by 13.2 % (n=7, P<0.05). Neither 1 μmol/L nor 10 μmol/L capsaicin had effects on the active curve of I_ A and I_ K. It was concluded that capsaicin could selectively inhibit the I_ A current, and this effect might involve in the analgesic mechanisms of capsaicin.
