Murine strain differences in contractile function are temperature- and frequency-dependent

Despite the widespread use of mice in the investigation of cardiac function, little is known as to what extent cardiac contractile function varies between different murine strains. We have investigated basic contractile function in isolated multicellular right ventricular trabeculae from three commonly used mouse strains (C57BL/6, SV129, and FVBN). Suitable trabeculae (1 mm long) occurred rather frequently in FVBN and SV129 mice (on average about 2 per heart), but only sporadically in C57BL/6 mice (on average only 1 per 3-4 mice). However, using similar sized preparations under experimental conditions closely mimicking those in vivo (37°C and frequencies between 8 and 12 Hz), contractile function was virtually identical. In addition, the magnitude of response to β-adrenergic stimulation was also indistinguishable between the strains. However, at subphysiological frequency, FVBN mice consistently displayed more developed force compared to C57/BL6 and SV129 mice. Furthermore, contractile performance at a subphysiological temperature and frequency, where studies on isolated myocardium often are performed, was also strain-dependent. We conclude that basic contractile function under near physiological conditions is preserved throughout various strains, but subphysiological conditions can have a profound effect on contractile performance. Hence, choice of strain can have important implications for cardiac contractile function under nonphysiological conditions.