Revisiting voltage-coupled H secretion in the collecting duct.

Experimental studies have shown that V-type ATPase-driven H secretion is dependent on transepithelial voltage. On this basis, the "voltage hypothesis" of urinary acidification by the collecting duct was derived. Accordingly, it has been supposed that the lumen-negative potential created by the reabsorption of Na via the epithelial Na channel (ENaC) enhances electrogenic H secretion via V-type H-ATPase.

Low potassium activation of proximal mTOR/AKT signaling is mediated by Kir4.2.

The renal epithelium is sensitive to changes in blood potassium (K). We identify the basolateral K channel, Kir4.2, as a mediator of the proximal tubule response to K deficiency.

High dietary K intake inhibits proximal tubule transport.

The impact of chronic dietary K loading on proximal tubule (PT) function was measured using free-flow micropuncture along with measurements of overall kidney function, including urine volume, glomerular filtration rate, and absolute and fractional Na and K excretion in the rat. Feeding animals a diet with 5% KCl [high K (HK)] for 7 days reduced glomerular filtration rate by 29%, increased urine volume by 77%, and increased absolute K excretion by 202% compared with rats on a 1% KCl [control K (CK)] diet. HK did not change absolute Na excretion but significantly increased fraction excretion of Na (1.

Regulation of glomerulotubular balance. IV. Implication of aquaporin 1 in flow-dependent proximal tubule transport and cell volume.

The water channel aquaporin-1 (AQP1) is the principal water pathway for isotonic water reabsorption in the kidney proximal tubule (PT). We investigated flow-mediated fluid () and [Formula: see text] ([Formula: see text]) reabsorption in PTs of the mouse kidney by microperfusion in wild-type (WT) and AQP1 knockout (KO) mice. Experiments were simulated in an adaptation of a mathematical model of the rat PT.

A mathematical model of the rat kidney. IV. Whole kidney response to hyperkalemia.

The renal response to acute hyperkalemia is mediated by increased K secretion within the connecting tubule (CNT), flux that is modulated by tubular effects (e.g., aldosterone) in conjunction with increased luminal flow.

Sex difference in kidney electrolyte transport III: Impact of low K intake on thiazide-sensitive cation excretion in male and female mice.

We compared the regulation of the NaCl cotransporter (NCC) in adaptation to a low-K (LK) diet in male and female mice. We measured hydrochlorothiazide (HCTZ)-induced changes in urine volume (UV), glomerular filtration rate (GFR), absolute (ENa, EK), and fractional (FENa, FEK) excretion in male and female mice on control-K (CK, 1% KCl) and LK (0.1% KCl) diets for 7 days.

ENaC and ROMK channels in the connecting tubule regulate renal K+ secretion.

We measured the activities of epithelial Na channels (ENaC) and ROMK channels in the distal nephron of the mouse kidney and assessed their role in the process of K+ secretion under different physiological conditions. Under basal dietary conditions (0.5% K), ENaC activity, measured as amiloride-sensitive currents, was high in cells at the distal end of the distal convoluted tubule (DCT) and proximal end of the connecting tubule (CNT), a region we call the early CNT (CNTe).

Restoration of proximal tubule flow-activated transport prevents cyst growth in polycystic kidney disease.

Flow-activated Na+ and HCO3- transport in kidney proximal tubules (PT) underlies relatively constant fractional reabsorption during changes in glomerular filtration rate (GFR) or glomerulotubular balance (GTB). In view of hypothesized connections of epithelial cilia to flow sensing, we examined flow-activated transport in 3 polycystic kidney disease-related mouse models based on inducible conditional KO of Pkd1, Pkd2, and Kif3a. PTs were harvested from mice after gene inactivation but prior to cyst formation, and flow-mediated PT transport was measured.

A mathematical model of the rat kidney. III. Ammonia transport.

Ammonia generated within the kidney is partitioned into a urinary fraction (the key buffer for net acid excretion) and an aliquot delivered to the systemic circulation. The physiology of this partitioning has yet to be examined in a kidney model, and that was undertaken in this work. This involves explicit representation of the cortical labyrinth, so that cortical interstitial solute concentrations are computed rather than assigned.

A mathematical model of the rat kidney. II. Antidiuresis.

Kidney water conservation requires a hypertonic medullary interstitium, NaCl in the outer medulla and NaCl and urea in the inner medulla, plus a vascular configuration that protects against washout. In this work, a multisolute model of the rat kidney is revisited to examine its capacity to simulate antidiuresis. The first step was to streamline model computation by parallelizing its Jacobian calculation, thus allowing finer medullary spatial resolution and more extensive examination of model parameters.

Accurate measurement of fast endocytic recycling kinetics in real time.

The fast turnover of membrane components through endocytosis and recycling allows precise control of the composition of the plasma membrane. Endocytic recycling can be rapid, with some molecules returning to the plasma membrane with a half time <5 min. Existing methods to study these trafficking pathways utilize chemical, radioactive or fluorescent labeling of cell surface receptors in pulse-chase experiments, which require tedious washing steps and manual collection of samples.

Sex difference in kidney electrolyte transport II: impact of K intake on thiazide-sensitive cation excretion in male and female mice.

We studied sex differences in response to high K (HK) intake on thiazide-sensitive cation (Na and K) excretion in wild-type (WT) and ANG II receptor subtype 1a (ATR) knockout (KO) mice. Renal clearance experiments were performed to examine Na-Cl cotransporter (NCC) activity on mice fed with control and HK (5% KCl, 7 days) diets. Hydrochlorothiazide (HCTZ)-induced changes in urine volume, glomerular filtration rate, absolute Na and K excretion, and fractional excretion were compared.

Regulation of renal Na transporters in response to dietary K.

Changes in the expression of Na transport proteins were measured in the kidneys of mice with increased dietary K intake for 1 wk. The epithelial Na channel (ENaC) was upregulated, with enhanced expression of full-length and cleaved forms of α-ENaC and cleaved γ-ENaC. At the same time, the amount of the NaCl cotransporter NCC and its phosphorylated form decreased by ~50% and ~80%, respectively.

Gender difference in kidney electrolyte transport. I. Role of AT receptor in thiazide-sensitive Na-Cl cotransporter activity and expression in male and female mice.

We studied gender differences in Na-Cl cotransporter (NCC) activity and expression in wild-type (WT) and AT receptor knockout (KO) mice. In renal clearance experiments, urine volume (UV), glomerular filtration rate, absolute Na (E) and K (E), and fractional Na (FE) and K excretion were measured and compared at peak changes after bolus intravenous injection of hydrochlorothiazide (HCTZ; 30 mg/kg). In WT, females responded more strongly than males to HCTZ, with larger fractional increases of UV (7.

Responses of distal nephron Na transporters to acute volume depletion and hyperkalemia.

We assessed effects of acute volume reductions induced by administration of diuretics in rats. Direct block of Na transport produced changes in urinary electrolyte excretion. Adaptations to these effects appeared as alterations in the expression of protein for the distal nephron Na transporters NCC and ENaC.

Regulation of glomerulotubular balance: flow-activated proximal tubule function.

The purpose of this review is to summarize our knowledge and understanding of the physiological importance and the mechanisms underlying flow-activated proximal tubule transport. Since the earliest micropuncture studies of mammalian proximal tubule, it has been recognized that tubular flow is an important regulator of sodium, potassium, and acid-base transport in the kidney. Increased fluid flow stimulates Na and HCO absorption in the proximal tubule via stimulation of Na/H-exchanger isoform 3 (NHE3) and H-ATPase.

A mathematical model of the rat kidney: K-induced natriuresis.

A model of the rat nephron (Weinstein. 308: F1098-F1118, 2015) has been extended with addition of medullary vasculature. Blood vessels contain solutes from the nephron model, plus additional species from the model of Atherton et al.

The fast-recycling receptor Megalin defines the apical recycling pathway of epithelial cells.

The basolateral recycling and transcytotic pathways of epithelial cells were previously defined using markers such as transferrin (TfR) and polymeric IgA (pIgR) receptors. In contrast, our knowledge of the apical recycling pathway remains fragmentary. Here we utilize quantitative live-imaging and mathematical modelling to outline the recycling pathway of Megalin (LRP-2), an apical receptor with key developmental and renal functions, in MDCK cells.

Flow-activated proximal tubule function underlies glomerulotubular balance.

Flow-modulated salt and water transport in proximal tubules has been recognized for more than four decades. Recent work has made major progress in defining the underlying cellular mechanisms. First, we demonstrated that perfusion-absorption balance is present in the isolated perfused proximal tubule of the mouse kidney, and thus is independent of neuronal control and systemic hormonal regulation.