WATER PERMEABILITY OF BRUSH-BORDER MEMBRANE-VESICLES FROM KIDNEY PROXIMAL TUBULE

Brush border membrane vesicles (BBMV) maintain an initial hydrostatic pressure difference between the intra- and extravesicular medium, whic h causes membrane strain and surface area expansion (Several, Macey & Moura, 1997). This has not been taken into account in prior osmotic wa ter permeability P-f-evaluations. In this paper, we find further evide nce for the pressure in the variation of stopped-flow light scattering traces with different vesicle preparations. Response to osmotic shock is used to estimate water permeability in BBMV prepared with buffers of different osmolarities (18 and 85 mosM). Data analysis includes the dissipation of both osmotic and hydrostatic pressure gradients. P-f v alues were of the order of 4 x 10(-3) cm sec(-1) independent of the os molarity of the preparation buffer. Arrhenius plots of P-f vs. 1/T wer e linear, showing a single activation energy of 4.6 kcal mol(-1). The initial osmotic response which is significantly retarded is correlated with the period of elevated hydrostatic pressure. We interpret this a s an inhibition of P-f caused by membrane strain and suggest how this inhibition may play a role in cell volume regulation in the proximal t ubule.