Power-law behavior of beat-rate variability in monolayer cultures of neonatal rat ventricular myocytes

It is known that extracardiac factors (nervous, humoral, and hemodynamic) p articipate in the power-law behavior of heart-rate variability. To assess w hether intrinsic properties of cardiac tissue might also be involved, beat- rate variability was studied in spontaneously beating cell cultures devoid of extracardiac influences. Extracellular electrograms were recorded from m onolayer cultures of neonatal rat ventricular myocytes under stable incubat ing conditions for up to 9 hours. The beat-rate time series of these record ings were examined in terms of their Fourier spectra and their Hurst scalin g exponents. A non-0 Hurst exponent was found in 21 of 22 preparations (0.3 9+/-0.09; range, 0.11 to 0.45), indicating the presence of fractal self-sim ilarity in the beat-rate time series. The same preparations exhibited power -law behavior of the power spectra with a power-law exponent of - 1.36+/-0. 24 (range, - 1.04 to -1.96) in the frequency range of 0.001 to 1 Hz. Furthe rmore, it was found that the power-law exponent was nonstationary over time . These results indicate that the power-law behavior of heart-rate variabil ity is determined not only by extracardiac influences but also by component s intrinsic to cardiac tissue. Furthermore, the presence of power-law behav ior in monolayer cultures of cardiomyocytes suggests that beat-rate variabi lity might be determined by the complex nonlinear dynamics of processes occ urring at the level of the cellular network, eg, interactions among a large number of cell oscillators or metabolic regulatory systems.