Membrane polarization at the excitation threshold induced by external electric fields in cardiomyocytes of rats at...

External electric fields (E), used for cardiac pacing and defibrillation/cardioversion, induce a spatially variable change in cardiomyocyte transmembrane potential (ΔV_m) that depends on cell geometry and E orientation. This study investigates E-induced ΔV_m in cardiomyocytes from rats at different ages, which show marked size/geometry variation. Using a tridimensional numerical electromagnetic model recently proposed (NM3D), it was possible: (a) to evaluate the suitability of the simpler, prolate spheroid analytical model (PSAM) to calculate amplitude and location of ΔV_m maximum (ΔV_max) for E = 1 V.cm^-1; and (b) to estimate the ΔV_max required for excitation (ΔV_T) from experimentally determined threshold E values (E_T). Ventricular myocytes were isolated from neonatal, weaning, adult, and aging Wistar rats. NM3D was constructed as the extruded 2D microscopy cell image, while measured minor and major cell dimensions were used for PSAM. Acceptable ΔV_m estimates can be obtained with PSAM from paralelepidal cells for small θ. E_T, but not ΔV_T, was higher for neonate cells. ΔV_T was significantly greater in the cell from older animals, which indicate lower responsiveness to E associated with aging, rather than with altered cell geometry/dimensions. ΔV_T might be used as a non-invasive indicator of cell excitability as it is little affected by cell geometry/size.