Temperature-dependent increase in the calcium sensitivity and acceleration of activation of ANO6 chloride channel variants

Sci Rep. 2019 Apr 30;9(1):6706. doi: 10.1038/s41598-019-43162-1.

Abstract

Anoctamin-6 (ANO6) belongs to a family of calcium (Ca2+)-activated chloride channels (CaCCs), with three splicing variants (V1, V2, and V5) showing plasma membrane expression. Unlike other CaCCs, ANO6 requires a non-physiological intracellular free calcium concentration ([Ca2+]i > 1 μM) and several minutes for full activation under a whole-cell patch clamp. Therefore, its physiological role as an ion channel is uncertain and it is more commonly considered a Ca2+-dependent phospholipid scramblase. Here, we demonstrate that physiological temperature (37 °C) increases ANO6 Ca2+ sensitivity under a whole-cell patch clamp; V1 was activated by 1 μM [Ca2+]i, whereas V2 and V5 were activated by 300 nM [Ca2+]i. Increasing the temperature to 42 °C led to activation of all ANO6 variants by 100 nM [Ca2+]i. The delay time for activation of the three variants was significantly shortened at 37 °C. Notably, the temperature-dependent Ca2+-sensitisation of ANO6 became insignificant under inside-out patch clamp, suggesting critical roles of unknown cytosolic factors. Unlike channel activity, 27 °C but not 37 °C (physiological temperature) induced the scramblase activity of ANO6 at submicromolar [Ca2+]i (300 nM), irrespective of variant type. Our results reveal a physiological ion conducting property of ANO6 at 37 °C and suggest that ANO6 channel function acts separately from its scramblase activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anoctamins / genetics
  • Anoctamins / metabolism*
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • HEK293 Cells
  • Humans
  • Patch-Clamp Techniques
  • Phospholipases A2 / metabolism
  • Phospholipid Transfer Proteins / genetics
  • Phospholipid Transfer Proteins / metabolism*
  • Temperature

Substances

  • ANO6 protein, human
  • Anoctamins
  • Phospholipid Transfer Proteins
  • Phospholipases A2
  • Calcium