Effect of antidiuretic hormone on water and solute permeation, and the activation energies for these processes, in mammalian cortical collecting tubules: evidence for parallel ADH-sensitive pathways for water and solute diffusion in luminal plasma membranes.

Abstract

The present studies were designed to assess the ways in which antidiuretic hormone (ADH) alters water and solute permeation across isolated, rabbit cortical collecting tubules. In earlier work, it was observed: that ADH produced a tenfold increment inPf (cm per sec), the osmotic water permeability coefficient, and a fourfold increment inPDw (cm per sec), the diffusional water permeability coefficient; that small hydrophilic solutes such as urea, thiourea and acetamide (each having oil/water partition coefficients≦0.0008) had vanishingly low permeation coefficients and unity reflection coefficients, even in the presence of ADH; that lumen to bath osmosis involved a transcellular route; and, that the disparity betweenPf andPDw, either with or without ADH, could be rationalized in terms of cellular diffusion constraints, i.e., that water transport across luminal membranes was diffusional.