Hydrostatic pressure in epidermal cells is dependent on Ca-mediated contractions.

Volume/osmotic pressure relationships were compared in Xenopus epidermal cells treated with the calcium antagonist lanthanum and in control cells. In lanthanum-treated cells the volume was found to be proportional to the reciprocal of the osmotic pressure in the hypotonic range, but not in the control cells. This difference is interpreted as being caused by contractions of the actomyosin system in control cells, which require external calcium. On the basis of the different slopes of the measurements under these two conditions the contractile force of the cells in isotonic conditions was calculated to be 0.96 x 10(5)Nm-2. The observation that in hypotonic media the cell body is enlarged in the direction of movement provides evidence that the cell body/lamella transition region is the part of the cell that contracts most during locomotion. By analysing cell speed in media with varying osmotic pressures, the relationship between internal pressure and cell locomotion was revealed.