A minimal isoform of the TMEM16A protein associated with chloride channel activity

https://doi.org/10.1016/j.bbamem.2011.05.017Get rights and content
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Abstract

TMEM16A protein, also known as anoctamin-1, has been recently identified as an essential component of Ca2+-activated Cl channels. We previously reported the existence of different TMEM16A isoforms generated by alternative splicing. In the present study, we have determined the functional properties of a minimal TMEM16A protein. This isoform, called TMEM16A(0), has a significantly shortened amino-terminus and lacks three alternative segments localized in the intracellular regions of the protein (total length: 840 amino acids). TMEM16A(0) expression is associated with Ca2+-activated Cl channel activity as measured by three different functional assays based on the halide-sensitive yellow fluorescent protein, short-circuit current recordings, and patch-clamp technique. However, compared to a longer isoform, TMEM16(abc) (total length: 982 amino acids), TMEM16A(0) completely lacks voltage-dependent activation. Furthermore, TMEM16A(0) and TMEM16A(abc) have similar but not identical responses to extracellular anion replacement, thus suggesting a difference in ion selectivity and conductance. Our results indicate that TMEM16A(0) has the basic domains required for anion transport and Ca2+-sensitivity. However, the absence of alternative segments, which are present in more complex isoforms of TMEM16A, modifies the channel gating and ion transport ability.

Highlights

Two isoforms of the TMEM16A chloride channel were analyzed by functional assays. Both isoforms are activated by calcium and transport anions. The shorter isoform, TMEM16A(0), is devoid of voltage-dependence. Alternative splicing modifies the properties of TMEM16A-associated ion channels.

Abbreviations

CaCC
Ca2+-activated Cl channel
YFP
yellow fluorescent protein

Keywords

Chloride channel
Alternative splicing
Intracellular calcium
Patch-clamp

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1

Present address: Dip. Psichiatria e Neurobiologia, Universita` di Pisa, via Bonanno 6, 56126 Pisa, Italy.