Evidence for permanent water channels in the basolateral membrane of an ADH-sensitive epithelium

Abstract

The transepithelial water permeability in frog urinary bladder is believed to be essentially dependent on the ADH-regulated apical water permeability. To get a better understanding of the transmural water movement, the diffusional water permeability (Pd) of the basolateral membrane of urinary bladder was studied. Access to this post-luminal barrier was made possible by "perforating" the apical membrane with amphotericin B. The addition of this antibiotic increased Pd from 1.12 +/- 0.10 x 10(-4) cm/sec (n = 7) to 4.08 +/- 0.33 x 10(-4) cm/sec (n = 7). The effect of mercuric sulfhydryl reagents, which are commonly used to characterize water channels, was tested on amphotericin B-treated bladders. HgCl2 (10(-3) M) decreased Pd by 52% and parachloromercuribenzoic acid (pCMB) (1.4 x 10(-4) M) by 34%. The activation energy for the diffusional water transport was found to increase from 4.52 +/- 0.23 kcal/mol (n = 3), in the control situation, to 9.99 +/- 0.91 kcal/mol (n = 4) in the presence of 1.4 x 10(-4) M pCMB. Our second approach was to measure the kinetics of water efflux, by stop-flow light scattering, on isolated epithelial cells from urinary bladders. pCMB (0.5 or 1.4 x 10(-4) M) was found to inhibit water exit by 91 +/- 2%. These data strongly support the existence of proteins responsible for water transport across the basolateral membrane, which are permanently present.

The hydroosmotic response of frog urinary bladder to serosal hypertonicity is dependent on adenylate cyclase for its maintenance and affected by [Cl−]ochanges

“…There is evidence for permanent water channels in the basolateral membrane of frog bladder epithelial cells; these channels are blocked by the presence of mercurials (HgCl 2 and P-chloromercuribenzene sulfonate) in the serosal bathing solution (58). Our functional studies with HgCl 2 (Fig.…”

Effect of mercuric chloride on electrical parameters and anion fluxes in the toad skin

“…A number of studies have been made describing the effects of Hg 2+ on transport processes in amphibian membranes, most of them related to blockade of apical water channels, and involving mainly exposure of the epidermal border of the skin to the cation (Ibarra et.al., 1989(Ibarra et.al., , 1990Van Der Goot et al, 1991;Grosso et al, 1993Grosso et al, , 1994.…”