Decoupling of heart muscle cells: Correlation with increased cytoplasmic calcium activity and with changes of nexus ultrastructure

Gerhard Dahl, Gerrit Isenberg

Research output: Contribution to journalArticle

121 Scopus citations

Abstract

Purkinje fibers of the sheep heart were exposed to (a) 0.1 mm dihydro-ouabain (DHO), followed by (b) 0.1 mm DHO in Na-free solution or to (c) 1 mm dinitrophenol (DNP). The degree of electrical decoupling was characterized in terms of the inside longitudinal resistance ri as measured with a 3-microelectrode voltage-clamp technique. Procedure a increased ri by a factor of 3.7±1.1 (mean±sd), b by a factor of 9.8±2.2, whereas in c incomplete voltage control indicated nearly complete uncoupling. Intracellular calcium activity (aCai) was monitored with a microelectrode system. At control conditions aCai was below 0.1 μm. The procedures listed above increased aCai to (a) 4±1.5 μm, (b) 8±2 μm, and (c) 36±12 μm. The increase of aCai was in good correlation with the changes in core resistance. Effects on nexus ultrastructure, investigated with freeze-fracture techniques, are shown in histograms. At control conditions, the particle diameter distributed around a single peak (8.3±0.5 nm). Procedures b and c induced a second population at 10.8 nm; increased decoupling reduced the control population in favor of the 10.8 nm population. Decoupling enlarged the width of the nexus gap by a factor of 1.6; again, the control population decreased in favor of a new population. In the decoupled state the height of the particle was smaller. Pits on the E-face displayed a more regular array and a nearly unchanged center-to-center spacing. Separation into several peaks was not possible due to scatter of the data. We interpret the findings to mean that elevated aCai induces a conformational change of the nexus subunits which corresponds to a transition from an open to a closed state. The conformational change can be formally described by a particle contraction which disrupts the continuity with the particle of the adjacent membrane. Purkinje fibers exposed to DNP for 1 hr showed thinned (7.7±0.5 mm) and elongated particles. We suggest that this is a secondary event and not a precursor of functional uncoupling.

Original languageEnglish (US)
Pages (from-to)63-75
Number of pages13
JournalThe Journal of Membrane Biology
Volume53
Issue number1
DOIs
StatePublished - Feb 1 1980
Externally publishedYes

Keywords

  • freeze fracture EM
  • heart
  • intracellular calcium
  • Nexus
  • uncoupling

ASJC Scopus subject areas

  • Physiology
  • Cell Biology
  • Biophysics

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