Gestational changes in mechanical properties of skinned muscle tissues of human myometrium

We developed a technique to obtain very thin myometrial muscle strips that allowed comparison of characteristic features of contraction from the same strip under intact and membrane-permeable ("skinned") conditions. Absolute tension development per unit of cross-sectional area induced by high potassium and oxytocin concentrations in the intact condition, or by Ca2+ in the skinned condition, markedly increased in human myometrium at term compared with the nonpregnant state. The maximum tension in skinned strips was 8.3 mN/mm2 in nonpregnant strips and 47.5 mN/mm2 at term (both obtained at 10 mumol/L Ca2+). The Ca2+ sensitivity of the contractile proteins in skinned strips also increased at term compared with the nonpregnant state; the half-maximal response of Ca2+ sensitivity was 0.7 mumol/L in the nonpregnant state and 0.3 mumol/L at term. These results suggest that in human myometrium both the amount of contractile proteins and their sensitivity to Ca2+ may increase at term compared with the nonpregnant state.