title: TMEM16F is a component of a Ca2+-activated Cl- channel but not a volume-sensitive outwardly rectifying Cl- channel.
abstract: TMEM16 (transmembrane protein 16) proteins, which possess eight putative transmembrane domains with intracellular NH2- and COOH-terminal tails, are thought to comprise a Cl(-) channel family. The function of TMEM16F, a member of the TMEM16 family, has been greatly controversial. In the present study, we performed whole cell patch-clamp recordings to investigate the function of human TMEM16F. In TMEM16F-transfected HEK293T cells but not TMEM16K- and mock-transfected cells, activation of membrane currents with strong outward rectification was found to be induced by application of a Ca(2+) ionophore, ionomycin, or by an increase in the intracellular free Ca(2+) concentration. The free Ca(2+) concentration for half-maximal activation of TMEM16F currents was 9.6 μM, which is distinctly higher than that for TMEM16A/B currents. The outwardly rectifying current-voltage relationship for TMEM16F currents was not changed by an increase in the intracellular Ca(2+) level, in contrast to TMEM16A/B currents. The Ca(2+)-activated TMEM16F currents were anion selective, because replacing Cl(-) with aspartate(-) in the bathing solution without changing cation concentrations caused a positive shift of the reversal potential. The anion selectivity sequence of the TMEM16F channel was I(-) > Br(-) > Cl(-) > F(-) > aspartate(-). Niflumic acid, a Ca(2+)-activated Cl(-) channel blocker, inhibited the TMEM16F-dependent Cl(-) currents. Neither overexpression nor knockdown of TMEM16F affected volume-sensitive outwardly rectifying Cl(-) channel (VSOR) currents activated by osmotic swelling or apoptotic stimulation. These results demonstrate that human TMEM16F is an essential component of a Ca(2+)-activated Cl(-) channel with a Ca(2+) sensitivity that is distinct from that of TMEM16A/B and that it is not related to VSOR activity.
authors: Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. takshimi@pha.u-toyama.ac.jp
authors: Takahiro
authors: T
authors: Shimizu
authors: Takahiro
authors: T
authors: Iehara
authors: Kaori
authors: K
authors: Sato
authors: Takuto
authors: T
authors: Fujii
authors: Hideki
authors: H
authors: Sakai
authors: Yasunobu
authors: Y
authors: Okada
mesh_terms: D000075368:Anoctamins; D002118:Calcium / Q000378:metabolism*; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D049294:Phospholipid Transfer Proteins / Q000378:metabolism* / Q000502:physiology
chemical_list: C555078:ANO6 protein, human; D000075368:Anoctamins; D065101:Chloride Channel Agonists; D018118:Chloride Channels; D049294:Phospholipid Transfer Proteins; D002118:Calcium