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NEUROPHARMACOLOGY

Effects of -Dendrotoxin on K⁺ Currents and Action Potentials in Tetrodotoxin-Resistant Adult Rat Trigeminal Ganglion Neurons

Department of Physiology, Nippon Dental University, School of Dentistry at Tokyo, Fujimi-cho, Chiyoda-ku, Tokyo, Japan

To determine whether the -dendrotoxin (-DTX)-sensitive current [D current, slow inactivating transient current (I_D)] contributes to the modification of neuronal function in small-diameter adult rat trigeminal ganglion (TG) neurons insensitive to 1 µM tetrodotoxin (TTX), we performed two different types of experiments. In the voltage-clamp mode, two distinct K⁺ current components, a fast inactivating transient current (I_A) and a dominant sustained current (I_K), were identified. -DTX (0.1 µM), ranging from 0.001 to 1 µM, maximally decreased I_A by approximately 20% and I_K by approximately 16.1% at a +50-mV step pulse, and 0.1 µM -DTX application increased the number of action potentials without changing the resting membrane potential. Irrespective of the absence and presence of 0.1 µM -DTX, applications of 4-aminopyridine (4-AP; 0.5 mM) and tetraethylammonium (TEA; 2 mM) inhibited approximately 50% inhibition of I_A and I_K, respectively. 4-AP (0.5 mM) depolarized the resting membrane potential and increased the number of action potentials in the absence or presence of 0.1 µM -DTX. TEA prolonged the duration of action potentials in the absence or presence of 0.1 µM -DTX. These results suggest that I_D contributes to the modification of neuronal function in adult rat TTX-resistant TG neurons, but after the loss of I_D due to 0.1 µM -DTX application, 4-AP (0.5 mM) and TEA (2 mM) still regulate the intrinsic firing properties of action potential number and shape.

Address correspondence to: Shinki Yoshida, Department of Physiology, Nippon Dental University, School of Dentistry at Tokyo, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan. E-mail: shinki{at}tokyo.ndu.ac.jp

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