Abstract
TMEM16A and TMEM16B are calcium-activated chloride channels (CaCCs) with important functions in mammalian physiology. Whether distant relatives of the vertebrate TMEM16 families also form CaCCs is an intriguing open question. Here we report that a TMEM16 family member from Drosophila melanogaster, Subdued (CG16718), is a CaCC. Amino acid substitutions of Subdued alter the ion selectivity and kinetic properties of the CaCC channels heterologously expressed in HEK 293T cells. This Drosophila channel displays characteristics of classic CaCCs, thereby providing evidence for evolutionarily conserved biophysical properties in the TMEM16 family. Additionally, we show that knockout flies lacking subdued gene activity more readily succumb to death caused by ingesting the pathogenic bacteria Serratia marcescens, suggesting that subdued has novel functions in Drosophila host defense. DOI: http://dx.doi.org/10.7554/eLife.00862.001.
Highlights
TMEM16A (Caputo et al, 2008; Schroeder et al, 2008; Yang et al, 2008) and, a different family member, TMEM16B (Pifferi et al, 2009) encode the classic calcium-activated chloride channels (CaCCs) in various mammalian tissues
Subdued was expressed in human embryonic kidney (HEK) 293T cells, a common heterologous expression system for electrophysiological studies of CaCCs (Caputo et al, 2008; Schroeder et al, 2008; Yang et al, 2008)
In these experiments with calcium infused from the whole-cell patch clamp pipette into the cytosol, rectification decreased over time as current amplitude increased
Summary
TMEM16A (Caputo et al, 2008; Schroeder et al, 2008; Yang et al, 2008) and, a different family member, TMEM16B (Pifferi et al, 2009) encode the classic calcium-activated chloride channels (CaCCs) in various mammalian tissues. TMEM16A regulates fluid secretion in submandibular glands, (Yang et al, 2008; Romanenko et al, 2010) as well as on the epithelia of airway surfaces (Rock et al, 2009) This channel modulates arterial (Manoury et al, 2010; Bulley et al, 2012), tracheal (Huang et al, 2012a), and gastrointestinal smooth muscle tone (Hwang et al, 2009), and has been observed to play a role in noxious heat sensing in the peripheral nervous system (Cho et al, 2012). TMEM16B is expressed in photoreceptor terminals (Stohr et al, 2009), where CaCCs are hypothesized to stabilize presynaptic membrane potential (Lalonde et al, 2008) This channel gives rise to the majority of recorded CaCC current in hippocampal pyramidal neurons (Huang et al, 2012b) and olfactory sensory neurons (Billig et al, 2011)
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