Mechanical properties of brush border membrane vesicles from kidney proximal tubule

The mechanical properties of brush border membrane vesicles, BBMV, from rabbit kidney proximal tubule cells, were studied by measuring the initial and final equilibrium volumes of vesicles subjected to different osmotic shocks, using cellobiose as the impermeant solute in the preparation buffer. An elevated intracellular hydrostatic pressure was inferred from osmotic balance requirements in dilute solutions. For vesicles prepared in 18 and 85 mosM solutions, these pressures are close to 17 mosM (290 mm Hg). The corresponding membrane surface tension is 6.0 x 10(-5) N cm-1 while the membrane surface area is expanded by at least 2.2%. When these vesicles are exposed to very dilute solutions the internal hydrostatic pressure rises to an estimated 84 mosM (1444 mm Hg) just prior to lysis. The corresponding maximal surface tension (pre-lysis) is 18.7 x 10(-5) N cm-1, and the maximal expansion of membrane area is 6.8%. The calculated area compressibility elastic modulus was 2.8 x 10(-3) N cm-1.