Mechanisms of proximal proton secretion in BBM of herbivorous, omnivorous, and carnivorous species.

The mechanisms of proton secretion by the proximal brush-border membrane (BBM) were compared in carnivorous (dog), omnivorous (human, pig, rat), and herbivorous (rabbit, hamster) species. The activity of the proton pump (V-type bafilomycin-sensitive H(+)-adenosinetriphosphatase) and of the Na+/H+ exchanger (amiloride-sensitive quenching of acridine orange fluorescence), the two major proton secretion mechanisms, was measured. The enzymatic activity of the H(+)-adenosinetriphosphatase activity was measured in intact (endosomes) and solubilized (0.

Cross-talk between the Na(+)-K(+)-ATPase and the H(+)-ATPase in proximal tubules in suspension.

The cellular energy required for the activity of the Na(+)-K(+)-ATPase and of the H(+)-ATPase was estimated in intact proximal tubules in suspension. Both the fall in oxygen consumption (directly measured) and NADH oxidation (as estimated from exogenous substrate metabolism) were measured before and following application of ouabain (1 mM) to inhibit the sodium pump, following bafilomycin (0.1 mM) to inhibit the proton pump or following a combination of these inhibitors.

Basolateral membrane potassium channels in rabbit cortical thick ascending limb.

The nature of K exit across the basolateral membrane of rabbit cortical thick ascending limb (CTAL) was investigated using the patch clamp technique. The basolateral membrane was exposed by mild collagenase treatment (0.1 U/ml), and a K-selective inwardly rectifying channel was identified.

Intracellular potassium activity in mammalian proximal tubule: effect of perturbations in transepithelial sodium transport.

Intracellular potassium activity (alpha Ki) was measured in control conditions in mid-cortical rabbit proximal convoluted tubule using two methods: (i) by determination of the K+ equilibrium potential (EK) using Ba(2+)-induced variations in the basolateral membrane potential (VBL) during transepithelial current injections and (ii) with double-barrel K-selective microelectrodes. Using the first method, the mean VBL was -48.5 +/- 3.

Regulation of basolateral membrane potential after stimulation of Na+ transport in proximal tubules.

We have previously shown that stimulation of apical Na-coupled glucose and alanine transport produces a transient depolarization of basolateral membrane potential (Vbl) in rabbit proximal convoluted tubule (PCT, S1 segment). The present study is aimed at understanding the origin of the membrane repolarization following the initial effect of addition of luminal cotransported solutes. Luminal addition of 10-15 mM L-alanine produced a rapid and highly significant depolarization of Vbl (20.