Osmotic equilibrium and elastic properties of eel intestinal vesicles

Changes in volume of intestinal brush border membrane vesicles of the Europ ean eel Anguilla anguilla were measured as vesicles were exposed to media w ith different osmotic pressures. Preparing the vesicles in media of low osm otic pressure allowed the effects of a small hydrostatic pressure to become a significant factor in the osmotic equilibration. By applying LaPlace's l aw to relate pressure and volume and assuming a linear relation between mem brane tension and area expansion, we estimate an initial membrane tension a t 4.02 x 10(-5) N cm(-1) and an area compressibility elastic modulus at 0.8 7 x 10(-3) N cm(-1). The elastic modulus estimate falls in the low range of values reported for membranes from other tissues in other species. This lo wer modulus quantitatively accounts for why eel intestinal vesicles show me asurable changes in volume in hypotonic media while rabbit kidney vesicles do not.