Assessment ofg-dependent Cellular Gravitaxis: Determination of Cell Orientation from Locomotion Track

Movement of cells in the gravity field is principally affected in two ways: velocity and orientation. Experimental observation of gravitaxis in large cell populations can document the velocity and orientation of swimming tracks, but orientations of individual cells are not represented at low magnifications. Cell orientations may depart from track orientations due to superposition of sedimentation on cellular propulsion. Here, we show that determination of the sedimentation rate in addition to cell track parameters allows a reconstitution of cell orientation employing geometric principles. Published and original cellular data indicate that gravitactic orientation of cells swimming in the gravity field is superior to that suggested from the experimental tracks. Similar conclusions apply to cells which walk or glide along substrate surfaces. Calculation of cell orientation coefficients provides a basis for determinations of the acceleration-dependence of gravitaxis and for quantitative tests on physical and/or physiological principles of cellular gravitaxis.