Activity-independent targeting of mTOR to lysosomes in primary osteoclasts.

Mammalian target of rapamycin (mTOR) is activated by numerous stimuli, including amino acids and growth factors. This kinase is part of the mTOR complex 1 (mTORC1) which regulates cell proliferation, differentiation, and autophagy. Active mTORC1 is located on lysosomes and has been reported to disassociate from the lysosomal surface in the absence of amino acids.

Escherichia coli Heat-Stable Enterotoxin Mediates Na+/H+ Exchanger 4 Inhibition Involving cAMP in T84 Human Intestinal Epithelial Cells.

The enterotoxigenic Escherichia coli strains lead to diarrhoea in humans due to heat-labile and heat-stable (STa) enterotoxins. STa increases Cl-release in intestinal cells, including the human colonic carcinoma T84 cell line, involving increased cGMP and membrane alkalization due to reduced Na+/H+ exchangers (NHEs) activity. Since NHEs modulate intracellular pH (pHi), and NHE1, NHE2, and NHE4 are expressed in T84 cells, we characterized the STa role as modulator of these exchangers.

Lysosomal pH Plays a Key Role in Regulation of mTOR Activity in Osteoclasts.

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase involved in the regulation of cell growth. It has been shown to play an important role in osteoclast differentiation, particularly at the earlier stages of osteoclastogenesis. mTOR activation and function, as part of mTORC1 complex, is dependent on lysosomal localization and the vacuolar H(+) -ATPase (V-ATPase) activity; however, the precise mechanism is still not well understood.

Uroguanylin inhibits H-ATPase activity and surface expression in renal distal tubules by a PKG-dependent pathway.

Cumulative evidence suggests that guanylin peptides play an important role on electrolyte homeostasis. We have previously reported that uroguanylin (UGN) inhibits bicarbonate reabsorption in a renal distal tubule. In the present study, we tested the hypothesis that the bicarbonaturic effect of UGN is at least in part attributable to inhibition of H(+)-ATPase-mediated hydrogen secretion in the distal nephron.

Functional role of glucose metabolism, osmotic stress, and sodium-glucose cotransporter isoform-mediated transport on Na+/H+ exchanger isoform 3 activity in the renal proximal tubule.

Na(+)-glucose cotransporter 1 (SGLT1)-mediated glucose uptake leads to activation of Na(+)-H(+) exchanger 3 (NHE3) in the intestine by a process that is not dependent on glucose metabolism. This coactivation may be important for postprandial nutrient uptake. However, it remains to be determined whether SGLT-mediated glucose uptake regulates NHE3-mediated NaHCO3 reabsorption in the renal proximal tubule.

Mechanisms underlying the inhibitory effects of uroguanylin on NHE3 transport activity in renal proximal tubule.

We previously demonstrated that uroguanylin (UGN) significantly inhibits Na(+)/H(+) exchanger (NHE)3-mediated bicarbonate reabsorption. In the present study, we aimed to elucidate the molecular mechanisms underlying the action of UGN on NHE3 in rat renal proximal tubules and in a proximal tubule cell line (LLC-PK(1)). The in vivo studies were performed by the stationary microperfusion technique, in which we measured H(+) secretion in rat renal proximal segments, through a H(+)-sensitive microelectrode.

Lysosomal calcium homeostasis defects, not proton pump defects, cause endo-lysosomal dysfunction in PSEN-deficient cells.

Presenilin (PSEN) deficiency is accompanied by accumulation of endosomes and autophagosomes, likely caused by impaired endo-lysosomal fusion. Recently, Lee et al. (2010.

Increased NHE3 abundance and transport activity in renal proximal tubule of rats with heart failure.

Heart failure (HF) is associated with a reduced effective circulating volume that drives sodium and water retention and extracellular volume expansion. We therefore hypothesized that Na(+)/H(+) exchanger isoform 3 (NHE3), the major apical transcellular pathway for sodium reabsorption in the proximal tubule, is upregulated in an experimental model of HF. HF was induced in male rats by left ventricle radiofrequency ablation.

A weak base-generating system suitable for selective manipulation of lysosomal pH.

pH varies widely among the different intracellular compartments. The establishment and maintenance of a particular pH appears to be critical for proper organellar function. This has been deduced from experiments where intraorganellar pH was altered by means of weak acids or bases, ionophores or inhibitors of the vacuolar H(+)-ATPase (V-ATPase).

Acid-base transport by the renal distal nephron.

The functional versatility of the distal nephron is mainly due to the large cytological heterogeneity of the segment. Part of Na+ uptake by distal tubules is dependent on Na+/H+ exchanger 2 (NHE2), implicating a role of distal convoluted cells also in acid-base homeostasis. In addition, intercalated (IC) cells expressed in distal convoluted tubules, connecting tubules and collecting ducts are involved in the final regulation of acid-base excretion.

Role of CFTR and ClC-5 in modulating vacuolar H+-ATPase activity in kidney proximal tubule.

Background/aims: It has been widely accepted that chloride ions moving along chloride channels act to dissipate the electrical gradient established by the electrogenic transport of H(+) ions performed by H(+)-ATPase into subcellular vesicles. Largely known in intracellular compartments, this mechanism is also important at the plasma membrane of cells from various tissues, including kidney. The present work was performed to study the modulation of plasma membrane H(+)-ATPase by chloride channels, in particular, CFTR and ClC-5 in kidney proximal tubule.

Posttranslational mechanisms associated with reduced NHE3 activity in adult vs. young prehypertensive SHR.

Abnormalities in renal proximal tubular (PT) sodium transport play an important role in the pathophysiology of essential hypertension. The Na(+)/H(+) exchanger isoform 3 (NHE3) represents the major route for sodium entry across the apical membrane of renal PT cells. We therefore aimed to assess in vivo NHE3 transport activity and to define the molecular mechanisms underlying NHE3 regulation before and after development of hypertension in the spontaneously hypertensive rat (SHR).

Regulation of Na+/H+ exchanger NHE3 by glucagon-like peptide 1 receptor agonist exendin-4 in renal proximal tubule cells.

The gut incretin hormone glucagon-like peptide 1 (GLP-1) is released in response to ingested nutrients and enhances insulin secretion. In addition to its insulinotropic properties, GLP-1 has been shown to have natriuretic actions paralleled by a diminished proton secretion. We therefore studied the role of the GLP-1 receptor agonist exendin-4 in modulating the activity of Na(+)/H(+) exchanger NHE3 in LLC-PK(1) cells.

Mechanisms underlying the long-term regulation of NHE3 by parathyroid hormone.

The activity of the Na(+)/H(+) exchanger NHE3 is regulated by a number of factors including parathyroid hormone (PTH). In the current study, we used a renal epithelial cell line, the opossum kidney (OKP) cell, to elucidate the mechanisms underlying the long-term effects of PTH on NHE3 transport activity and expression. We observed that NHE3 activity was reduced 6 h after addition of PTH, and this reduction persisted almost unaltered after 24 h.

NHE1, NHE2, and NHE4 contribute to regulation of cell pH in T84 colon cancer cells.

The isoforms of the Na+/H+ exchanger present in T84 human colon cells were identified by functional and molecular methods. Cell pH was measured by fluorescence microscopy using the probe BCECF. Based on the pH recovery after an ammonium pulse and determination of buffering capacity of these cells, the rate of H+ extrusion (JH) was 3.

Signaling pathways involved with the stimulatory effect of angiotensin II on vacuolar H+-ATPase in proximal tubule cells.

It has been documented that angiotensin II (ANG II) (10(-9) M) stimulates proton extrusion via H(+)-adenosine triphosphatase (ATPase) in proximal tubule cells. In the present study, we investigated the signaling pathways involved in the effects of ANG II on H(+)-ATPase activity and on the cytosolic free calcium concentration in immortalized rat proximal tubule cells, a permanent cell line derived from rat proximal tubules. The effects of ANG on pH(i) and [Ca(+2)](i) were assessed by the fluorescent probes, 2',7-bis (2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxy-methyl ester and fluo-4-acetoxy-methyl ester, in the absence of Na(+) to block the Na(+)/H(+) exchanger.

Increased NHE1 expression is associated with serum deprivation-induced differentiation in immortalized rat proximal tubule cells.

We studied the proton secretion mechanisms involved with pHi regulation in immortalized rat proximal tubule cells (IRPTC), a SV40-immortalized cell line derived from rat proximal tubule, and characterized the effects of serum deprivation on them. Using pHi measurements with the fluorescent probe BCECF, we demonstrated that the IRPTC express both Na+/H+ exchanger and H+-ATPase, but only NHE1 is modulated by serum deprivation. In these cells, 24 h of serum starvation increased pHi from 7.