• Michiko Nakamura, Do-Yeon Kim, and Il-Sung Jang.
• Department of Pharmacology, School of Dentistry, Kyungpook National University, Daegu 700-412, Republic of Korea; Brain Science & Engineering Institute, Kyungpook National University, Daegu 700-412, Republic of Korea.
• Brain Res. 2016 Nov 15; 1651: 44-52.

AbstractVoltage-gated Na+ channels in primary afferent neurons can be divided into tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na+ channels. Although previous studies have shown the acid modulation of TTX-R Na+ channels, the effect of acidic pH on tetrodotoxin-sensitive (TTX-S) Na+ channels is still unknown. Here we report the effect of acidic pH on TTX-S Na+ channels expressed in large-sized trigeminal ganglion (TG) neurons using a whole-cell patch clamp technique. The application of acidic extracellular solution decreased the peak amplitude of TTX-S currents (INa) in a pH-dependent manner, but weak acid (≥pH 6.0) had no inhibitory effect on TTX-S INa. Acidic pH (pH 6.0) shifted both the activation and steady-state fast inactivation relationships of TTX-S Na+ channels toward depolarized potentials. However, acidic pH (pH 6.0) had no effect on use-dependent inhibition in response to high-frequency stimuli, development of inactivation, and accelerated the recovery from inactivation of TTX-S Na+ channels, suggesting that TTX-S Na+ channels in large-sized TG neurons are less sensitive to acidic pH. Given that voltage-gated Na+ channels play a pivotal role in the generation and conduction of action potentials in neural tissues, the insensitivity of TTX-S Na+ channels expressed in large-sized TG neurons to acidic pH would ensure transmission of innocuous tactile sensation from orofacial regions at acidic pH conditions.Copyright © 2016. Published by Elsevier B.V.

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