Local shears, e.g. during catheterization or local ischemia, are known to induce extra systoles or arrhythmias. How exogenous shear force is distributed inside the cell is largely unknown and will be studied here.

Isolated myocytes were attached to cover-slips and deformed by displacing a cell attached stylus of calibra-ted stiffness in three directions. 3D confocal microscopy of membranes (ANEPPS stained) quantified bending of stylus to calculate applied force and outer cell contours, alignment and length of sarcomeres. - The shear properties were non-linear and anisotropic, i.e. the myocyte was least resistant to displacements imposed in the axis of the myofilaments. Deformation remained restricted to <12% of cell volume, it dissipated with distance from stylus along gradients that were steepest vertically and flattest axially. Vertical or lateral displacement of stylus by 5 or 10 mm displaced cytoplasm and mitochondria from indentation towards cell border, without effect on length and alignment of sarcomeres. Axial stretch or compression by 5 or 10 mm sheared the upper cell part versus the attached cell bottom and bended transversal tubules towards the stylus, thereby changing alignment and length of sarcomeres. Based on immunostaining, misaligning of sarcomeres and collagen in transversal tubules is discussed to pull and to activate integrin thereby triggering further signalling cascades that may modulate mechano-sensitive ion channels.