TMEM16F is a component of a Ca2+-activated Cl channel but not a volume-sensitive outwardly rectifying Cl channel

Takahiro Shimizu, Takahiro Iehara, Kaori Sato, Takuto Fujii, Hideki Sakai, Yasunobu Okada


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 Ca2+ ionophore, ionomycin, or by an increase in the intracellular free Ca2+ concentration. The free Ca2+ 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 Ca2+ level, in contrast to TMEM16A/B currents. The Ca2+-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 Ca2+-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 Ca2+-activated Cl channel with a Ca2+ sensitivity that is distinct from that of TMEM16A/B and that it is not related to VSOR activity.

  • anoctamin 6
  • anoctamin 10
  • Ca2+-activated Cl channel
  • volume-sensitive Cl channel
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