Length dependence of passive stiffness in single cardiac myocytes

Passive elastic properties have been studied in detergent-skinned isolated single cardiac myocytes of rat, guinea pig, and rabbit in an attempt to determine whether a measurable difference exists in passive cellular elastic characteristics of these mammalian species. Although the cross-sectional area of isolated cardiac myocytes is complex, a small but statistical difference appears to exist in the elastic modulus of detergent-skinned mammalian cardiac myocytes at 2.2 microns sarcomere length (SL) in the order rat is greater than rabbit, which is greater than guinea pig. The stiffness of rat cells increases least rapidly with increases in SL, and that of the rabbit cells increases most rapidly. In comparison with intact cardiac tissue in the literature, the proportion of stress contributed by skinned myocytes may be as much as half that of the trabeculae at 2.2 microns SL and approximately 10% of that of papillary muscles. Below 2.2 microns SL, the relative cellular proportion increases such that cellular elements may be a major contributor at 1.9 microns SL. Above 2.2 microns SL, the relative cellular contribution declines such that by 2.4 microns SL the cellular contribution is insignificant. It is concluded that at functional SLs intracellular elastic elements may contribute measurably to total cardiac passive elasticity, but at extended lengths the extracellular structures constitute the major limitation to extension.