Cardiac BIN1 folds T-tubule membrane, controlling ion flux and limiting arrhythmia

Nat Med. 2014 Jun;20(6):624-32. doi: 10.1038/nm.3543. Epub 2014 May 18.

Abstract

Cardiomyocyte T tubules are important for regulating ion flux. Bridging integrator 1 (BIN1) is a T-tubule protein associated with calcium channel trafficking that is downregulated in failing hearts. Here we find that cardiac T tubules normally contain dense protective inner membrane folds that are formed by a cardiac isoform of BIN1. In mice with cardiac Bin1 deletion, T-tubule folding is decreased, which does not change overall cardiomyocyte morphology but leads to free diffusion of local extracellular calcium and potassium ions, prolonging action-potential duration and increasing susceptibility to ventricular arrhythmias. We also found that T-tubule inner folds are rescued by expression of the BIN1 isoform BIN1+13+17, which promotes N-WASP-dependent actin polymerization to stabilize the T-tubule membrane at cardiac Z discs. BIN1+13+17 recruits actin to fold the T-tubule membrane, creating a 'fuzzy space' that protectively restricts ion flux. When the amount of the BIN1+13+17 isoform is decreased, as occurs in acquired cardiomyopathy, T-tubule morphology is altered, and arrhythmia can result.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Analysis of Variance
  • Animals
  • Arrhythmias, Cardiac / metabolism*
  • Base Sequence
  • Calcium / metabolism
  • Cloning, Molecular
  • DNA Primers / genetics
  • DNA Probes / genetics
  • Mice
  • Microscopy, Electron, Transmission
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Myocytes, Cardiac / metabolism*
  • Myocytes, Cardiac / ultrastructure
  • Nerve Tissue Proteins / metabolism*
  • Real-Time Polymerase Chain Reaction
  • Sarcolemma / metabolism*
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Adaptor Proteins, Signal Transducing
  • Bin1 protein, mouse
  • DNA Primers
  • DNA Probes
  • Nerve Tissue Proteins
  • Tumor Suppressor Proteins
  • Calcium