Mechanical properties of normal andmdx mouse sarcolemma: Bearing on function of dystrophin

Abstract

The tensile strength of the muscle fibre surface membrane was estimated (1) from the suction required to burst membrane patches and (2) by aspiration of sarcolemmal vesicles into micropipettes of uniform bore. Each method gave an average value close to 60 μN cm⁻¹ for the maximum tension sustainable by normal mouse sarcolemma and only slightly lower values for sarcolemma frommdx mice which lack dystrophin. The elastic modulus of area expansion, as measurable by pipette aspiration of sarcolemmal vesicles, was found to have an average value of 3160 μN cm⁻¹ for normal and 2770 μN cm⁻¹ formdx mouse sarcolemma. The tensile strength of the sarcolemma is much too small for any differences in it to be the basis for the different osmotic behaviour of normal andmdx muscle fibres reported recently (Menke & Jockusch, 1991). By analogy with the better understood origin of the osmotic fragility of different types of red blood cells, the higher osmotic fragility ofmdx muscle fibres is suggested to be of morphological origin. We postulate that dystrophin functions as an element of the submembrane cytoskeleton so as to maintain the normal folding which safeguards the sarcolemma against mechanical damage.