Kinetics of water transport in eel intestinal vesicles

Brush border membrane vesicles, BBMV, from eel intestinal cells or kidney p roximal tubule cells were prepared in a low osmolarity cellobiose buffer. T he osmotic water permeability coefficient PS for eel vesicles was not affec ted by pCMBS and was measured at 1.6 x 10(-3) cm sec(-1) at 23 degrees C, a value lower than 3.6 x 10(-3) cm sec(-1) exhibited by the kidney vesicles and similar to published values for Lipid bilayers. An activation energy E- a of 14.7 Kcal mol(-1) for water transport was obtained for eel intestine, contrasting with 4.8 Kcal mol(-1) determined for rabbit kidney proximal tub ule vesicles using the same method of analysis. The high value of E-a, as w ell as the low P-f for the eel intestine is compatible with the absence of water channels in these membrane vesicles and is consistent with the view t hat water permeates by dissolution and diffusion in the membrane. Further, the initial transient observed in the osmotic response of kidney vesicles, which is presumed to reflect the inhibition of water channels by membrane s tress, could not be observed in the eel intestinal vesicles. The Pf depende nce on the tonicity of the osmotic shock, described for kidney vesicles and related to the dissipation of pressure and stress at low tonicity shocks, was not seen with eel vesicles. These results indicate that the membranes f rom two volume transporter epithelia have different mechanisms of water per meation. Presumably the functional water channels observed in kidney vesicl es are not present in eel intestine vesicles. The elastic modulus of the me mbrane was estimated by analysis of swelling kinetics of eel vesicles follo wing hypotonic shock. The value obtained, 0.79 x 10(-3) N cm(-1), compares favorably with the corresponding value, 0.87 x 10(-3) N cm(-1), estimated f rom measurements at osmotic equilibrium.