Common channels for water and protons at apical and basolateral cell membranes of frog skin and urinary bladder epithelia. Effects of oxytocin, heavy metals, and inhibitors of H(+)-adenosine triphosphatase.

Abstract

We have compared the response of proton and water transport to oxytocin treatment in isolated frog skin and urinary bladder epithelia to provide further insights into the nature of water flow and H ÷ flux across individual apical and basolateral cell membrances. In isolated spontaneous sodium-transporting frog skin epithelia, lowering the pH of the apical solution from 7.4 to 6.4, 5.5, or 4.5 produced a fall in pH~ in principal cells which was completely blocked by amiloride (50 ~.M), indicating that apical Na ÷ channels are permeable to protons. When sodium transport was blocked by amiloride, the H ÷ permeability of the apical membranes of principal cells was negiligible but increased dramatically after treatment with antidiuretic hormone (ADH). In the latter condition, lowering the pH of the apical solution caused a voltage-dependent intracellular acidification, accompanied by membrane depolarization, and an increase in membrane conductance and transepithelial current. These effects were inhibited by adding Hg '÷ (100 o.M) or dicydohexylcarbodiimide (DCCD, to the apical bath. Net titratable H ÷ flux across frog skin was increased from 30 -+ 8 to 115 _ 18 neq-h-l-cm -~ (n = 8) after oxytocin treatment (at apical pH 5.5 and serosal pH 7.4) and was completely inhibited by DCCD (10 -5 M). The basolateral membranes of the principal cells in frog skin epithelium were found to be spontaneously permeable to H ÷ and passive electrogenic H ÷ transport across this membrane was not affected by oxytocin. Lowering the pH of the basolateral bathing solution (pHb) produced an intraceUular acidification and membrane depolarization (and an increase in conductance when the normal dominant K ÷ conductance of this membrane was abolished by Ba 2÷ 1 mM). These effects of low pH b were blocked by micromolar concentrations of heavy metals (Zn 2÷, Ni ~÷, Co 2÷, Cd ~+, and Hg~+). 750THE JOURNAL OF GENERAL PHYSIOLOGY • VOLUME 97. 1991 (50 mU/ml) produced a transepithelial current (3 p~A'cm -~ at pH b 5.5) which was blocked by 100 I~M of rig z+, Zn 2+, or Ni 2+ at the basolateral side, and by DCCD (10 -~' M) or Hg 2+ (100 p~M) from the apical side. The net hydroosmotic water flux (JH~o) induced by oxytocin in frog bladder sacs was blocked by inhibitors of H+-adenosine triphosphatase (ATPase). Diethylstilbestrol (DES 10 -5 M), oligomycin (10 -~ M), and DCCD (10 -~ M) preventedJH~o when present in the lumen. These effects cannot be attributed to inhibition of metabolism since cyanide (10 -4 M), or 2-deoxyglucose (10 -3 M) had no effect onJ~o. DCCD and oligomycin, which are known to interact with the F o proton channel of F~-F o H+-ATPase also appear to act directly on the apical water channel in glutaraldehyde-fixed bladders. The sulfhydryl group reagent n-ethylmaleimide (10 -4 M) which interacts with the F~-Fo-type H+-ATPase in renal epithelia as well as vacuolar H+-ATPase produced an 85% inibition of JH~o. Oxytocin failed to activate a net water flux when Zn 2÷ (100 ~M) or Hg z+ (100 ~M) were present in the serosal solution, ...

Cadmium and transport of ions and substances across cell membranes and epithelia

“…Voltage sensitive proton channels (DeCoursey and Cherny 2007) and epithelial proton and water channels (Harvey et al 1991) are sensitive to Cd 2? and other metals.…”

“…The cause can be impaired solute uptake, but possibly also a blockage of antidiuretic hormone sensitive water channels (see e.g. Harvey et al 1991). Effects on water channels and their role in fluid loss is a question that needs to be further explored.…”

Hydrogen ion currents in rat alveolar epithelial cells

“…There is strong indirect evidence for a H+ conductance in human neutrophils (Henderson et al, 1987(Henderson et al, , 1988; other examples are cited by Meech and Thomas (1987). Water channels of amphibian skin and urinary bladder appear to be permeable to protons and are blockable by heavy metals, but are not voltage-gated (Harvey et al, 1991). Renal epithelia apparently have H+ conductive pathways (Sabolic and Burckhardt, 1983).…”

Energization of sodium absorption by the H+-ATPase pump in mitochondria-rich cells of frog skin

“…Patch-clamp studies, as described here, of membrane conductance and capacitance of MR cells in situ in a polarized and functional epithelium offer unique opportunities to discover the mechanisms of ion transport regulation modulated by acid-base and hormonal challenges. This tool could also be used to probe further the analogy between proton channels and antidiuretic hormone water channels (Harris et al 1991;Harvey et al 1991).…”