title: Fluctuations in interbeat interval in rhythmic heart-cell clusters. Role of membrane voltage noise.
abstract: Small clusters of ventricular cells prepared from 7-d chick heart maintain spontaneous, stationary, rhythmic beating in culture for many hours. For clusters containing I-125 cells, mean interbeat interval (IBI) is 0.45 +/- 0.08 s and is independent of cell number (N), whereas, the coefficient of variation of IBI (C) is proportional to N-1/2. Because membrane voltage noise in such clusters would also be expected to vary as N-1/2, we propose a model relating fluctuation in IBI (sigma IBI) to voltage noise (sigma v). A simplified model consisting of random voltage fluctuations superimposed upon a linear pacemaker depolarization of slope a is used to analyze the N-dependent shape of the IBI histogram. Values of sigma v derived from the relation sigma IBI = sigma v/a, or calculated from the skewness of the measured IBI histograms, both agree well with those extrapolated from steady-state noise recorded from resting heart-cell aggregates.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D002642:Chick Embryo; D004594:Electrophysiology; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D008954:Models, Biological
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