Changes in permeability of the plasma membrane of myoblasts to fluorescent dyes with different molecular masses under sustained uniaxial stretching.

Deep tissue injury (DTI) is a serious pressure ulcer which onsets in skeletal muscle tissues adjacent to weight-bearing bony prominences. Recent literature points at sustained large deformations in muscle tissue, which translate to static stretching of the plasma membrane (PM) at the cell-scale, as the primary cause of accumulated cell death in DTI. It has been specifically suggested that prolonged exposure to large tensional PM strains interferes with normal cellular homeostasis, primarily by affecting transport through the PM which could become more permeable when stretched. In this context, using confocal imaging and fluorescence-activated cell sorter (FACS), we visualized and quantified here the uptake of fluorescent Dextran dye by myoblasts that were statically stretched uniaxially, up to physiological strains of 3%, 6% and 9%, using two different molecular masses for the Dextran (4kDa and 20kDa). The confocal and FACS studies provided consistent evidence that the permeability of the PM increased at large static deformations. Furthermore, the FACS data indicated that the kinetics of the PM permeability very likely depends on the size of the biomolecular marker. Both results were consistent with reports published in the neurotrauma literature on the kinetics of uptake of fluorescent biomolecules by dynamically stretched neurons; hence there are some analogues in the biomechanical pathways of cellular-level injury between DTI and impact insults. The present work provides additional empirical support to the theory of cell-scale deformation-diffusion damage in the etiology of DTI, and may lead to better understanding of time courses for onset of cellular damage in DTI, by exploring mass transport processes across the PM of the involved cells.