• KSBNS 2024


Original Article

Exp Neurobiol 2023; 32(3): 133-146

Published online June 30, 2023

© The Korean Society for Brain and Neural Sciences

Intracellular Loop in the Brain Isoforms of Anoctamin 2 Channels Regulates Calcium-dependent Activation

Dongsu Lee1†, Hocheol Lim1,2†, Jungryun Lee1, Go Eun Ha1, Kyoung Tai No1,2 and Eunji Cheong1*

1Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seoul 03722, 2The Interdisciplinary Graduate Program in Integrative Biotechnology & Translational Medicine, Yonsei University, Incheon 21983, Korea

Correspondence to: *To whom correspondence should be addressed.
TEL: 82-2-2123-5885, FAX: 82-2-2123-8284
These authors contributed equally to this article.

Received: December 27, 2022; Revised: May 12, 2023; Accepted: June 1, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Anoctamin 2 (ANO2 or TMEM16B), a calcium-activated chloride channel (CaCC), performs diverse roles in neurons throughout the central nervous system. In hippocampal neurons, ANO2 narrows action potential width and reduces postsynaptic depolarization with high sensitivity to Ca2+ at relatively fast kinetics. In other brain regions, including the thalamus, ANO2 mediates activity-dependent spike frequency adaptations with low sensitivity to Ca2+ at relatively slow kinetics. How this same channel can respond to a wide range of Ca2+ levels remains unclear. We hypothesized that splice variants of ANO2 may contribute to its distinct Ca2+ sensitivity, and thus its diverse neuronal functions. We identified two ANO2 isoforms expressed in mouse brains and examined their electrophysiological properties: isoform 1 (encoded by splice variants with exons 1a, 2, 4, and 14) was expressed in the hippocampus, while isoform 2 (encoded by splice variants with exons 1a, 2, and 4) was broadly expressed throughout the brain, including in the cortex and thalamus, and had a slower calcium-dependent activation current than isoform 1. Computational modeling revealed that the secondary structure of the first intracellular loop of isoform 1 forms an entrance cavity to the calcium-binding site from the cytosol that is relatively larger than that in isoform 2. This difference provides structural evidence that isoform 2 is involved in accommodating spike frequency, while isoform 1 is involved in shaping the duration of an action potential and decreasing postsynaptic depolarization. Our study highlights the roles and molecular mechanisms of specific ANO2 splice variants in modulating neuronal functions.

Graphical Abstract

Keywords: Anoctamin 2, Calcium-activated chloride channels, Splice variants, Calcium, Secondary protein structure, Molecular modeling