[Determination, using a piezo-impulse method, of iso-osmotic permeability of the apical membrane of epithelium]. / Détermination par une méthode piézoimpulsionnelle de la "perméabilité isoosmotique" de la membrane apicale d'un épithélium.

A frog skin, mechanically held on the mucosal side separates two Ringer solutions. It is submitted to an hydrostatic pressure difference delta P varying between 2 and 120 mb. Water permeability P (delta P) delta pi = 0 is determined with a piezo-impulse method. The rapid variation of permeability within the 2-25 mb range indicates a reversible closing of the junctions. The limiting value Pisol for high delta P is the isoosmotic permeability of the apical membrane.

Osmotic effects of tubulin (brain contractile protein) polymerization. A possible role in cell salt and water regulation.

Polymerization changes of tubulin (a contractile protein of brain) induced by temperature increase from 4 degrees C to 25 degrees C caused a large (85%) decrease in measured osmotic pressure of the tubulin. This indicates that contractile proteins within cells may be expected to play a significant role in cell osmotic equilibria.