Article

Inhibitory effects of lappaconitine on the neuronal isoforms of voltage-gated sodium channels

Authors: Yan-fen Li1,2, Yue-ming Zheng2,3, Yong Yu4, Yong Gan2,3, Zhao-bing Gao2,3
1 Shanghai Key Laboratory of Bio-Energy Crops, School of Life Sciences, Shanghai University, Shanghai 200444, China
2 CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
3 University of Chinese Academy of Sciences, Beijing 100049, China
4 Department of Neurosurgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China
Correspondence to: Yong Gan: ygan@simm.ac.cn, Zhao-bing Gao: zbgao@simm.ac.cn,
DOI: 10.1038/s41401-018-0067-x
Received: 10 March 2018
Accepted: 17 May 2018
Advance online: 10 July 2018

Abstract

Lappaconitine (LA) has been widely used for postoperative and cancer pain control. LA exhibits excellent analgesic activity with a longer effective time than common local anesthetics such as tetracaine and bupivacaine. However, the mechanisms underlying the featured analgesic activity of LA remain largely unknown. Here, we report that LA is an inhibitor of voltage-gated sodium channel 1.7 (Nav1.7) stably expressed in human embryonic kidney (HEK293) cells. LA inhibited Nav1.7 in a voltage-dependent manner with an IC50 value (with 95% confidence limits) of 27.67 (15.68–39.66) µmol/L when the cell was clamped at −70 mV. In comparison with the quick and reversible inhibition of Nav1.7 by tetracaine and bupivacaine, the inhibitory effect of LA was rather slow and irreversible. It took more than 10 min to achieve steady-state inhibition when LA (300 µmol/L) was administered. Unlike tetracaine and bupivacaine, LA affected neither the voltage-dependent activation nor the inactivation of the channels. Five residues in domain III and domain IV have been reported to be critical for the effects of the two local anesthetics on Nav channels. But our mutant study revealed that only two residues (F1737, N1742) located in domain IV were necessary for the inhibitory activity of LA. The slow onset, irreversibility, and lack of influence on channel activation and inactivation accompanied with the different molecular determinants suggest that LA may inhibit Nav1.7 channels in a manner different from local anesthetics. These results may help to understand the featured analgesic activity of LA, thus benefiting its application in the clinic and future drug development.
Keywords: voltage-gated sodium channel 1.7; analgesics; lappaconitine; tetracaine; bupivacaine

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