Fig. 2.

Effect of membrane tension on sperm cell motility. (A) Dot plots of the speed of whole cell translocation. Red: hypotonic medium (130 mOsm); blue: isotonic media (175 mOsm); green: 150 μm deoxycholate (DC); purple: hypertonic media (275 mOsm); black: strong hypertonic media (350 mOsm). Significant differences are marked with asterisks. (B) Dot plots of the spread area of crawling cells and their aspect ratio (lamellipodium long axis divided by cell body width) under different treatments with labels and color coding as in A. Significant differences are marked with asterisks. (C) The relation of tether force (+/− SEM) to cell treatment. Legend is as for A. Seven to 18 cells were measured per condition, and tether forces were recorded as soon as the force stabilized (10–30 s), before tube relaxation could set in. The difference between Iso and DC/Hyper/Hyper++ is significant (marked with an asterisk for DC only). (Left) A tube (arrowhead) extending between the bead (Top) and the lamellipodia of a pronase-activated sperm cell (Bottom). The sperm cell is out of focus. (D) Tube under flow experiment to evaluate effect of hypotonic treatment on short time scales. A tube was pulled at time zero and 10 s later, water began to be injected (red curve, arrowhead) or not (blue curve). Evolution of the tether force was recorded over time and reproducibly showed a spike after water injection (red curve, arrow) before relaxing, whereas tubes of control cells just relaxed (blue curve). In C, bar = 2 μm.