Ion channel and lipid scramblase activity associated with expression of TMEM16F/ANO6 isoforms

Paolo Scudieri, Emanuela Caci, Arianna Venturini, Elvira Sondo, Giulia Pianigiani, Carla Marchetti, Roberto Ravazzolo, Franco Pagani, Luis J V Galietta

Research output: Contribution to journalArticlepeer-review

Abstract

TMEM16F, also known as ANO6, is a membrane protein that has been associated with phospholipid scramblase and ion channel activity. However, the characteristics of TMEM16F-dependent channels, particularly the ion selectivity, are a matter of debate. Furthermore, the direct involvement of TMEM16F in phospholipid scrambling has been questioned. We studied the properties of different TMEM16F variants generated by alternative splicing. Using whole-cell patch-clamp recordings, we found that V1, V2 and V5 variants generated membrane currents activated by very high (micromolar) intracellular Ca2+ concentrations and positive membrane potentials. These variants showed different degrees of Ca2+ sensitivity and kinetics of activation but similar ion permeability, characterized by a slight selectivity for Cl- over Na+. A fourth variant (V3) showing a unique carboxy-terminus was devoid of activity, in agreement with its intracellular localization. We also measured scramblase activity using the binding of annexin V to detect phosphatidylserine on the cell surface. V1, V2 and V5 variants were associated with calcium-dependent phosphatidylserine externalization. Interestingly, introduction of an activating mutation, D409G, produced a marked increase in the apparent Ca2+ sensitivity of TMEM16F-dependent channels. In parallel, this mutation also enhanced the extent of phosphatidylserine externalization that occurred even under resting conditions. These results support the conclusion that TMEM16F proteins are directly involved in dual activity, as a phospholipid scramblase and as an ion channel. Journal compilation

Original languageEnglish
Pages (from-to)3829-3848
Number of pages20
JournalJournal of Physiology
Volume593
Issue number17
DOIs
Publication statusPublished - Sep 1 2015

ASJC Scopus subject areas

  • Physiology

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