Cellular constraints to diffusion

Abstract

A B S T R A C T These experiments were intended to evaluate the effects of antidiuretic hormone (ADH) on dissipative water transport in cortical collecting tubules isolated from rabbit kidney. In the absence of ADH, the osmotic (Pf, cm sec-') and diffusional (PDW cm sec') water permeability coefficients were, respectively, 6±6 and 4.7±1.3 (SD). When ADH was added to the bathing solutions, Pf and PDw rose to, respectively, 186±38 and 14.2±1.6 (SD). In the absence of ADH, the tubular cells were flat and the lateral intercellular spaces were closed when the perfusing and bathing solutions were, respectively, hypotonic and isotonic; in the presence of ADH, the cells swelled and the intercellular spaces dilated. These data suggest that ADH increased the water permeability of the luminal membranes of the tubules.It was possible that the ADH-dependent Pf/PD, ratio was referable to the resistance of the epithelial cell layer (exclusive of luminal membranes) to water diffusion (RDW, sec cm-1). RDI was referable to cellular constraints to diffusion; for these solutes, the latter were 12-25 times greater than in water. Accordingly, it is possible that the ADHdependent Pf/PDW ratio was also due to cellular constraints to diffusion. INTRODUCTIONCertain biological tissues, such as the skin and urinary bladder of amphibians and the collecting tubule of the mammalian kidney, have a primary role in the regulation of water homeostasis. The purpose of this paper is to examine the mode of dissipative water transport across isolated collecting tubule segments from mammalian kidney, and the way in which antidiuretic hormone (ADH)' modifies these transport processes.Ussing and his coworkers (1, 2) first proposed that water traversed aqueous channels in anuran skin, and that ADH increased the size of such pores. The rate of osmotic water flow across anuran skin was considerably greater than might be expected for a diffusion process (1), i.e., the osmotic water permeability coefficient (Pf, cm sec-1) was greater than the diffusional water permeability coefficient (PDW, cm sec') ; and, ADH increased the Pf/PDW ratio. Koefoed-Johnsen and Ussing rationalized the difference between Pt and

The effects of antidiuretic hormone (ADH) on solute and water transport in the mammalian nephron

“…Table 1 lists PI and Po~ values measured in this nephron segment at 23 ~ PI is more than fourfold higher than Pew in the absence of ADH, and more than 13-fold higher in the presence of the hormone (Grantham & Burg, 1966;Schafer & Andreoli, 1972a).…”

“…where C* is the integrated average luminal tracer concentration (Grantham & Burg, 1966;Schafer & Andreoli, 1972a). Alternatively, water permeability may be measured by imposing a transepithelial osmolality difference (Arc, atm) and measuring the resulting net volume flow d~ (cm/sec).…”

“…2). Furthermore, within 10min after adding A D H to the bathing solution, the cells swell and bulge apically, and the cell margins become sharply outlined (Schafer & Andreoli, 1972a). Ganote et al (1968) and Grantham et al (1969), using transmission electron micrographs of tubules fixed at various stages in the A D H response, showed that, in the presence of lumen-to-bath osmotic flow, there was an increase in the apex-to-base cell height, intracellular vacuolation, and distension of lateral intercellular spaces.…”

“…Interval between small divisions in photomicrograph scale is 2.13 gm. (Adapted from Andreoli and 1966; Ganote et al 1968;Grantham et al, 1969;Schafer & Andreoli, 1972a).…”

“…In the case of cortical collecting tubules, the ADHdependent P:/PDw ratio of approximately 13 (Table 1) requires, in terms of large pore theory, an effective pore radius of ~13/k (Schafer & Andreoli, 1972a). Yet as indicated above (Table 1), cortical collecting tubules are virtually impermeable to small hydrophilic solutes such as urea (effective hydrodynamic radius ---2.2 •), both in the presence and absence of ADH.…”