Intrinsic characteristics of the proton pump in the luminal membrane of a tight urinary epithelium. The relation between transport rate and delta mu H.

Abstract

A number of tight urinary epithelia, as exemplified by the turtle bladder, acidify the luminal solution by active transport of H* across the luminal cell membrane . The rate of active H + transport (JH) decreases as the electrochemical potential difference for H + [o~H = AH(lumen) -~H(serosa)] across the epithelium is increased . The luminal cell membrane has a low permeability for H' equivalents and a high electrical resistance compared with the basolateral cell membrane . Changes in j,4 thus reflect changes in active H+ transport across the luminal membrane . To examine the control of JH by A/<H in the turtle bladder, transepithelial electrical potential differences (AO) were imposed at constant acid-base conditions or the luminal pH was varied at 04, = 0 and constant serosal Pco s and pH . When the luminal compartment was acidified from pH 7 to 4 or was made electrically positive, JH decreased as a linear function of D~H as previously described . When the luminal compartment was made alkaline from pH 7 to 9 or was made electrically negative, JH reached a maximal value, which was the same whether the AAIi was imposed as a ApH or a Dip. The nonlinear JH vs . Alai relation does not result from changes in the number of pumps in the luminal membrane or from changes in the intracellular pH, but is a characteristic of the H' pumps themselves . We propose a general scheme, which, because of its structural features, can account for the nonlinearity of theJH vs . A~H relations and, more specifically, for the kinetic equivalence of the effects of the chemical and electrical components of D~H . According to this model, the pump complex consists of two components : a catalytic unit at the cytoplasmic side of the luminal membrane, which mediates the ATP-driven H* translocation, and a transmembrane channel, which mediates the transfer of H + from the catalytic unit to the luminal solution . These two components may be linked through a buffer compartment for H + (an antechamber) .Address reprint requests to Dt .

Collecting Duct Intercalated Cell Function and Regulation

“…(32,58). In the case of H 1 -ATPase, two other main factors affect its function at the plasma membrane: the pH difference across the apical membrane and the transepithelial potential difference (59). For example, this pump mediates H 1 transport at a rate that is 0 when the luminal pH is ,4.5, while the transport rate of the pump is saturated at a pH of 7.0-8.0.…”

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

“…7. In turtle urinary bladder (Andersen, Silveira & Steinmetz, 1985) and frog skin (Ehrenfeld, Garcia-Romeu & Harvey, 1985) the active H+ current is depending on membrane potential in such a way that it is reduced if the apical membrane is hyperpolarized and accelerated if the apical membrane is depolarized by Vt clamps. There are clear indications that MR cells in 212 H+ PUMP OF MITOCHONDRIA-RICH CELLS toad skin contain an apical Na+ conductance which is sensitive to amiloride (Larsen et al 1987).…”

Flow-dependent transport in a mathematical model of rat proximal tubule

“…Nevertheless, these models have supported the primacy of luminal membrane Na ϩ /H ϩ exchange in determining the rate of overall proximal Na ϩ reabsorption (47). Even with the inclusion of formate, the impact of luminal membrane Cl Ϫ /HCO 2 Ϫ antiporter density on proximal Na ϩ and Cl Ϫ fluxes was small relative to the effect that changes in NHE3 activity had on these fluxes. More recently, the proximal tubule models have been used to examine the coordination of luminal and peritubular transport pathways, required to preserve the integrity of cell volume and composition during variations on Na ϩ reabsorption (51,52).…”