A Method to Characterize Calcium Activity in Stimulated Cultures of Cardiac Myocytes

Abstract

Cardiac function and disease constitutes a complex physiological process involving several biophysical scales, from the stochastic dynamics of a single calcium release channel to the calcium signal of a single myocyte and the activation of contraction across a cardiac tissue. Integration of signals from several of these scales requires specific tools to study their interdependence.We present a method for automatic detection of calcium signals in cultured cardiomyocytes subjected to external field stimulation. The method is applied to a sequence of confocal fluorescence images, and provides information on both the calcium activity in individual myocytes, the global calcium signal of the imaged field, as well as the propagation of the calcium signal across the cell culture.The approach first segments each cell in the culture and computes its average calcium activity. An automatic classification method then identifies the response of each cell among six different dynamical regimes a) uniform response, b) alternating response, c) irregular response, d) calcium waves, e) phase-lock (conduction block) or f) inactive. The system computes the area, the full duration at half maximum (FDHM), the resting value and the peak of the calcium transient of each cell. Subsequently, it maps the distribution of cells from each group within the imaged field.Finally, the method generates an isochronal map of the activation of each cell in the culture as the calcium front propagates across the culture, computing the linear and angular velocities as well as the propagation direction.The resulting data can be used to quantify how abnormal calcium regulation at the single-cell level affects the propagation of the calcium signal in a myocyte culture. The method is also suitable for a quantitative comparison of the effects of pharmacological or genetic treatments of cell cultures.