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.
Grégoire Courtine, Jocelyne Bloch, Jordan Squair
Yves Perriard, Yoan René Cyrille Civet, Stefania Maria Aliki Konstantinidi, Amine Benouhiba, Quentin Philippe Mario De Menech, Sloan Zammouri