Sodium current properties of primary skeletal myocytes and cardiomyocytes derived from different mouse strains

Abstract

The mouse has become the preferred animal for genetic manipulations. Because of the diverse genetic backgrounds of various mouse strains, these can manifest strikingly different characteristics. Here, we studied the functional properties of currents through voltage-gated sodium channels in primary cultures of skeletal myocytes and cardiomyocytes derived from the three commonly used mouse strains BL6, 129/Sv, and FVB, by using the whole-cell patch-clamp technique. We found strain-specific sodium current function in skeletal myocytes, which could partly be explained by differences in sodium channel isoform expression. In addition, we found significant effects of cell source (neonatal or adult animal-derived) and variation of the differentiation time period. In contrast to skeletal myocytes, sodium current function in cardiomyocytes was similar in all strains. Our findings are relevant for the design and proper interpretation of electrophysiological studies, which use excitable cells in primary culture as a model system.

Fig. 1

Comparison of the current decay kinetics in skeletal myocytes derived from different mouse strains. Typical examples of current decay at I_max are displayed in the top left image. The arrows indicate the time points at which current decay half-times were measured. These represent the time periods between the current peak and the time point at which the current had decayed to 50%. In the graphs, current decay half-times were plotted against the membrane voltage (steps between −30 and +10 mV from a holding potential of −120 mV) for myocytes derived from neonatal (early and late differentiation window) and adult mice. The lines connect single data points. Data are expressed as means±SE. *p<0.05 and **p<0.01 indicate a significant difference between the three strains at certain potentials revealed by ANOVA

Fig. 2

Sequential program and original traces of a typical TTX experiment. The currents were elicited by depolarizing voltage steps between −90 and +50 mV from a holding potential of −120 mV and were recorded from a skeletal myocyte in the early differentiation window derived from a neonatal BL6 mouse in 140 mM sodium bath solution. This ensured adequate current amplitudes also in the presence of 1 μM TTX. Currents during superfusion with bath solution containing 1 μM TTX were recorded 60 s after TTX application was begun

Fig. 3

Typical examples of original current traces with the corresponding IV relationships (upper panel) and steady-state slow inactivation curves (lower panel) of cardiomyocytes (a) and skeletal myocytes (b) of the 129 strain. The experiments were performed on cardiomyocytes derived from neonatal mice and from skeletal myocytes derived from neonatal mice in the early differentiation window. The pulse protocols used to elicit the currents are given in the text of the “Results”, and the fitting procedures (function F1 for IV relationships and function F3 for steady-state slow inactivation curves, solid lines) are described in the “Materials and methods”