AJP - Renal Physiology, Vol 259, Issue 2 366-F371, Copyright © 1990 by American Physiological Society
High proton flux through membranes containing antidiuretic hormone water channels
H. W. Harris Jr, D. Kikeri, A. Janoshazi, A. K. Solomon and M. L. Zeidel
Renal Division, Brockton/West Roxbury Veterans Administration Medical Center, Massachusetts 02132.
Antidiuretic hormone (ADH) stimulation of toad urinary bladder granular
cells causes simultaneous increases in transepithelial water and H+
permeabilities (PF and PH+, respectively), suggesting that ADH-elicited
water channels inserted into granular cell apical membranes might be
permeable to both water and H+. We have previously used self-quenching
fluorophores entrapped within endocytic vesicles selectively retrieved from
water-permeable apical membranes to measure vesicle PF. The membranes of
these vesicles possess an extremely high PF such that our measurements
provide only minimum estimates of vesicle PF and have limited our ability
to quantitate the properties of ADH water channels. We therefore
quantitated vesicle PH+ using similar rapid mixing techniques. Vesicle PH+
was 5.1 +/- 0.5 x 10(-3) cm/s. Activation energy of this process was 3.6
+/- 0.6 kcal/mol, indicative of H+ flux through an aqueous channel. The
mercurial reagent, para-chloromercuribenzenesulfonate (PCMBS), which
inhibits ADH-stimulated transepithelial PF in intact bladders by 50-60%,
inhibited vesicle PH+ by 55%. N-Ethylmaleimide and phloretin, which do not
alter ADH-stimulated PF, did not affect vesicle PH+. We conclude that
membranes containing ADH water channels possess substantial PH+ that likely
reflects proton flux through water channels. The apparent high PH+ of the
ADH water channel may have important implications for intracellular
trafficking of these water channels in ADH-responsive epithelial cells.
