Uniform action potential repolarization within the sarcolemma of in situ ventricular cardiomyocytes

Biophys J. 2009 Mar 18;96(6):2532-46. doi: 10.1016/j.bpj.2008.12.3896.

Abstract

Previous studies have speculated, based on indirect evidence, that the action potential at the transverse (t)-tubules is longer than at the surface membrane in mammalian ventricular cardiomyocytes. To date, no technique has enabled recording of electrical activity selectively at the t-tubules to directly examine this hypothesis. We used confocal line-scan imaging in conjunction with the fast response voltage-sensitive dyes ANNINE-6 and ANNINE-6plus to resolve action potential-related changes in fractional dye fluorescence (DeltaF/F) at the t-tubule and surface membranes of in situ mouse ventricular cardiomyocytes. Peak DeltaF/F during action potential phase 0 depolarization averaged -21% for both dyes. The shape and time course of optical action potentials measured with the water-soluble ANNINE-6plus were indistinguishable from those of action potentials recorded with intracellular microelectrodes in the absence of the dye. In contrast, optical action potentials measured with the water-insoluble ANNINE-6 were significantly prolonged compared to the electrical recordings obtained from dye-free hearts, suggesting electrophysiological effects of ANNINE-6 and/or its solvents. With either dye, the kinetics of action potential-dependent changes in DeltaF/F during repolarization were found to be similar at the t-tubular and surface membranes. This study provides what to our knowledge are the first direct measurements of t-tubule electrical activity in ventricular cardiomyocytes, which support the concept that action potential duration is uniform throughout the sarcolemma of individual cells.

Publication types

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

MeSH terms

  • Action Potentials*
  • Analysis of Variance
  • Animals
  • Cell Membrane / physiology
  • Chrysenes
  • Fluorescence
  • Fluorescent Dyes
  • In Vitro Techniques
  • Kinetics
  • Mice
  • Microelectrodes
  • Microscopy, Confocal
  • Myocytes, Cardiac / physiology*
  • Myocytes, Cardiac / ultrastructure
  • Quaternary Ammonium Compounds
  • Sarcolemma / physiology*

Substances

  • ANNINE-6plus
  • Chrysenes
  • Fluorescent Dyes
  • Quaternary Ammonium Compounds