Role of proton pump of mitochondria‐rich cells for active transport of chloride ions in toad skin epithelium.

Abstract

SUMMARY1. Active Cl-currents were studied in short-circuited toad skin epithelium in which the passive voltage-activated Cl-current is zero. Under visual control doublebarrelled microelectrodes were used for impaling principal cells from the serosal side, or for measuring the pH profile in the solution bathing the apical border.2. The net inward (active) 36CP-flux of 27+8 pmol s-1 cm-2 (16) (mean + s.E.M (number of observations)) was abolished by 2 mM-CN-(6-3 ± 3-5 pmol s-1 cm-2 (8)). The active flux was maintained in the absence of active Na+ transport when the latter was eliminated by either 100 ,um-mucosal amiloride, replacement of mucosal Na+ with K+, or by 3 mM-serosal ouabain.3. In Ringer solution buffered by 24 mM-HCO3,-5 % CO2 mucosal amiloride reversed the short circuit current (ISC). The outward ISc was maintained when gluconate replaced mucosal Cl-, and it was reversibly reduced in C02-free 5 mM-Trisbuffered Ringer solution (pH = 7 40) or by the proton pump inhibitor oligomycin.These observations indicate that the source of the outward ISc is an apical proton pump.4. Amiloride caused principal cells to hyperpolarize from a basolateral membrane potential, Vb, of -73 + 3 (22) to -93 +1 mV (26), and superfusion with C02-free Trisbuffered Ringer solution induced a further hyperpolarization (Vb =-101 +1 mV (26)) which could be blocked by Ba2+. The C02-sensitive current changes were null at Vb = EK (potassium reversal potential, -106 + 2 mV (55)) implying that they are carried by K+ channels in the basolateral membrane. Such a response cannot account for the inhibition of the outward ISc which by default seems to be located to mitochondria-rich (MR) cells.5. In the absence of mucosal Cl-a pH gradient was built up above MR cells with pH = 7-02 + 0 04 (42) and pH increasing to 7X37 + 0X02 (10) above principal cells (pH = 7

Cyclic AMP‐and beta‐agonist‐activated chloride conductance of a toad skin epithelium.

“…Since the measured membrane potential of -100 mV was close to the potassium equilibrium potential, which in our preparation was -106 + 2 mV, n = 55 (Larsen, Willumsen & Christoffersen, 1992), our results indirectly indicate that a K+ conductance becomes activated by the increased intracellular [cyclic AMP]. To account for the increase in fRb such K+ conductance must be in the apical membrane.…”

Chloride currents of single mitochondria‐rich cells of toad skin epithelium.

“…For example, an efflux of protons is generated by an apical proton pump in MR cells (Page & Frazier, 1987;Ehrenfeld, Lacoste & Harvey, 1989;Harvey, 1992;Larsen, Willumsen & Christoffersen, 1992), and passive and active inward fluxes of Cl-have been localized to MR cells, with the active component energized by the apical proton pump (Vofute & Meyer, 1978;Larsen, 1991;. Finally, an apical amiloride-blockable Na+ influx mechanism and basolateral Na+-K+ pumps are present in MR cells, indicating that they also mediate active uptake of Na+ (Larsen, Ussing & Spring, 1987;Harvey, 1992;Rick, 1992).…”

Exposure of the gill epithelial cells of larval lampreys to an ion-deficient environment: a stereological study

“…We have previously suggested that the IMRCs in the ammocoete gills belong to the subtype A or C [11], which cannot be distinguished in the presence of H-ATPase and rod-shaped particles in their apical membrane alone. The view that many of the IMRCs in the ammocoete gill epithelium belong to the subtype C is supported by the observation of Reis-Santos and co-workers [7] that many of these cells show a strong cytoplasmic immunoreactivity for H + -ATPase, which is typical for this subtype [13,34]. Thus, an active H + secretion through the subtype A and C cells would not only provide the driving force for the uptake of Na + but also favour the uptake of Cl − through subtype C cells as the actively secreted H + can bind to the HCO 3 − as it leaves the cell through the apical membrane and thereby establish an HCO 3 − gradient across this membrane which would drive the uptake of Cl − [13].…”

“…On the basis of their ultrastructure and the presence of H + -ATPase and carbonic anhydrase, the lamprey IMRC is a type of epithelial cell that also occurs, for example, in the amphibian epidermis, the toad and turtle urinary bladders and renal collecting duct [7,11,13,30,31]. This cell type comprises three subtypes: one (A) containing the H + -ATPase in its apical membrane and an HCO 3 − /Cl − exchanger in its basolateral membrane, another (B) exhibiting the opposite locations of the H + pump and the anion exchanger and a third (C) in which the H + pump and the anion exchanger are both located in the apical membrane [32][33][34]. Whereas the subtypes A and B are involved in acid-base regulation, secreting H + or HCO 3 − , respectively, the subtype C has been held responsible for the uptake of Cl − [32][33][34].…”

“…This cell type comprises three subtypes: one (A) containing the H + -ATPase in its apical membrane and an HCO 3 − /Cl − exchanger in its basolateral membrane, another (B) exhibiting the opposite locations of the H + pump and the anion exchanger and a third (C) in which the H + pump and the anion exchanger are both located in the apical membrane [32][33][34]. Whereas the subtypes A and B are involved in acid-base regulation, secreting H + or HCO 3 − , respectively, the subtype C has been held responsible for the uptake of Cl − [32][33][34]. In the epithelium of the turtle bladder, the apical surface area of subtype A cells becomes enlarged under acidotic conditions through exocytosis of cytoplasmic membranous tubules and vesicles containing the H + -ATPase [19,35].…”