Electrogenic active proton pump in Rana esculenta skin and its role in sodium ion transport.

Abstract

SUMMARY1. Kinetic and electrophysiological studies were carried out in the in vitro Rana esculenta skin, bathed in dilute sodium solution, to characterize the proton pump and coupling between sodium absorption (JNa+) and proton excretion (JH+).2. JNa+ and JH+ were both dependent on transepithelial potential (V'ms); hyperpolarizing the skin decreased JNa+ and increased JnH+; depolarization produced the opposite effects. These changes were accompanied by depolarization of the apical membrane potentialVfmc from -47 to -25 mV and an increase in apical membrane resistance of 30 % ; no significant effects on basolateral membrane potential (Vfc) and resistance (Rb) nor on shunt resistance (Rj) were observed. The proton pump appears to be localized at the apical membrane. 6. The proton pump was also inhibited by deoxygenation, oligomycin, dicyclohexylcarbodiimide and vanadate (100, 78, 83 and 100 % inhibition respectively). The variations ofJH+ and ofthe measured electrical currents were significantly correlated. These findings are supportive evidence of a primary active proton pump, electrogenic and strictly linked to aerobic metabolism.7. The current-voltage (I-V) relation of the proton pump was obtained as the difference in the I-V curves of the apical membrane extracted before and after proton-pump inhibition by ethoxzolamide during amiloride block ofsodium transport.The proton-pump current (Ip) was best described by a saturable exponential function of Vfmc. Maximal pump current (IWmX) was calculated to be 200 nequiv h-1 cm-2 at a Vmc of + 50 mV and the pump reversal potential ER was -130 mV. The effect of ethoxzolamide to depolarize Vfmc was dependent on the relation between Vfmc and ER. Maximal induced depolarization occurred at a Vmc of + 50 mV whereas ethoxzolamide exerted minimal effect on Vfmc when the ER was approached either by voltage clamping the apical membrane or by the addition of amiloride.8. We show that electroneutral sodium-proton countertransport is not the mechanism of active proton excretion in frog skin but that it is the proton excretion J. EHRENFELD, F. GARCIA-ROMEU AND B. J. HARVEY which provides a favourable electrical driving force for passive apical sodium entry. The apparent coupling between net proton and sodium fluxes depends on the relation between V1mc and ER and the effect of the sodium-electrode-like behaviour of the apical membrane on this relation.

Changing salinity induces alterations in hemolymph ion concentrations and Na+ and Cl– transport kinetics of the anal papillae in the larval mosquito,Aedes aegypti

“…The localization of the Vtype-H + -ATPase is consistent with the recorded acidification of the unstirred layer adjacent the anal papillae (Donini and O'Donnell, 2005). The V-type-H + -ATPase may serve to set up a negative potential across the apical membrane through the pumping of H + into the external medium, which would create conditions favorable for the electrodiffusive entry of Na + through channels across the apical membrane, similar to the scenario found in frog skin (Ehrenfeld et al, 1985) and freshwater fish gills (Lin and Randall, 1991). Indeed, A. Donini and others , Cl -and H + concentrations in the hemolymph within 6·h of transfer.…”

Cloning and Expression of Vacuolar Proton-Pumping ATPase Subunits in the Follicular Epithelium of the Bullfrog Endolymphatic Sac

“…In support of this model, a band 3-like anion exchanger has been shown to be present in MR cells of Bufo viridis (Devuyst et al, 1993). H + , which is transported from the MR cells to the skin surface by V-ATPase, is considered to facilitate Na + absorption (Ehrenfeld et al, 1985;1989).…”

V-type H+-ATPase and Na+,K+-ATPase in the gills of 13 euryhaline crabs during salinity acclimation

“…We propose that those crabs with an apical distribution of HA employ a mechanism similar to the freshwater mechanism in aquatic animals, including fish (for a review, see DeRenzis and Bornancin, 1984), amphibia (Ehrenfeld et al, 1985) and crustaceans (Weihrauch et al, 2001), to overcome osmotic stress (Wieczorek et al, 1999;Morris, 2001;Kirschner, 2004). In our study, five of the 13 species examined had an apical distribution of HA, implying that HA in these crabs is more responsive to salinity than NKA, and HA in these crabs participates in the osmoregulatory function.…”