Uniform action potential repolarization within the sarcolemma of in situ ventricular cardiomyocytes.
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.
Bu
Guixue
G
Department of Biomedical Engineering, Purdue School of Engineering and Technology, Indianapolis, Indiana 46202, USA.
Adams
Heather
H
Berbari
Edward J
EJ
Rubart
Michael
M
D000200:Action Potentials; D000704:Analysis of Variance; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002911:Chrysenes; D005453:Fluorescence; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D008839:Microelectrodes; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000648:ultrastructure; D000644:Quaternary Ammonium Compounds; D012508:Sarcolemma / Q000502:physiology*
C530581:ANNINE-6plus; D002911:Chrysenes; D005456:Fluorescent Dyes; D000644:Quaternary Ammonium Compounds