Lysosomal pH: a link between cell volume and metabolism

Läng, Florian; Busch, Gillian L.; Völkl, Harald; Häussinger, Dieter

doi:10.1042/bst0220502

Cited by 19 publications

(3 citation statements)

References 13 publications

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“…The data show a rapid and reversible alkalinization of intracellular endocytotic compartments and a simultaneous slight acidification of the cytosol in response to hypo-osmotic cell swelling; opposite pH changes occur in response to hyperosmotic cell shrinkage. Similar observations were made recently with respect to Acridine Orange fluorescence [8,31,32]. As shown here with FITC-dextran, the effects are not transient, but they are fully reversible upon normotonic re-exposure.…”

Section: Discussionsupporting

confidence: 91%

Effects of aniso-osmolarity and hydroperoxides on intracellular pH in isolated rat hepatocytes as assessed by (2′,7′)-bis(carboxyethyl)-5(6)-carboxyfluorescein and fluorescein isothiocyanate-dextran fluorescence

Schreiber

Stoll

Läng

et al. 1994

Biochemical Journal

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Freshly isolated rat hepatocytes were plated for 4-6 h and either loaded with (2',7)-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) or allowed to endocytose fluorescein isothiocyanate (FITC)-coupled dextran in order to study the effects of aniso-osmotic exposure and oxidative stress on cytosolic (pHcyt) and apparent vesicular pH (pHves) by single-cell fluorescence recordings. In the presence of normo-osmotic (305 mosmol/l) medium pHcyt was 7.23 +/- 0.03 (n = 108), whereas an apparent pH of 6.07 +/- 0.02 (n = 156) was found in the vesicular compartment accessible to endocytosed FITC-dextran. Substitution of 60 mM NaCl against 120 mM raffinose had no effect on pHcyt or apparent pHves, whereas addition of NH4Cl increased both pHcyt and apparent pHves. Hypo-osmotic cell swelling lowered pHcyt, whereas simultaneously apparent pHves increased. These effects were rapidly reversible upon re-institution of normo-osmotic media. Similarly, an increase of apparent pHves was observed when cell swelling was induced by Ba2+, glutamine or histidine. Conversely, hyperosmotic cell shrinkage due to addition of NaCl or raffinose led to a cytosolic alkalinization and a vesicular acidification. Both, H2O2 (0.2 mmol/l) and t-butyl-hydroperoxide (0.2 mmol/l) were without effect on pHcyt, but lowered apparent pHves by about 0.2 pH units. Ba2+ (1 mmol/l) diminished the acidifying effect of the hydroperoxides by about 50%. Pretreatment of the cells with colchicine, but not with lumicolchicine, largely abolished the effects of aniso-osmolarity and hydroperoxides on pHves. The data suggest that hepatocellular hydration affects the proton gradients built up across the membranes of endocytotic FITC-dextran-accessible compartments in a microtubule-dependent way. They further suggest that hydroperoxides induce vesicular acidification in a colchicine- and Ba(2+)-sensitive way. Because hydroperoxides induce Ba(2+)-sensitive cell shrinkage [Hallbrucker, Ritter, Lang, Gerok and Häussinger (1992) Eur. J. Biochem. 211, 449-458], the results are compatible with the view that hydroperoxide-induced cell shrinkage mediates vesicular acidification. It is concluded that modulation of vesicular pH by the hepatocellular hydration state may play a role in triggering some metabolic changes in response to cell swelling/shrinkage.

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Section: Discussionsupporting

confidence: 91%

Effects of aniso-osmolarity and hydroperoxides on intracellular pH in isolated rat hepatocytes as assessed by (2′,7′)-bis(carboxyethyl)-5(6)-carboxyfluorescein and fluorescein isothiocyanate-dextran fluorescence

Schreiber

Stoll

Läng

et al. 1994

Biochemical Journal

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“…regulation by cell volume is restricted to the 'early' endocytotic compartment, suggesting that lysosomal pH is not affected by cell volume. Thus, the previously hypothesized role of vesicular pH in the mediation of proteolysis control by cell volume [24,25] probably does not involve lysosomes (as was discussed in [7,24,25]), but may largely be exerted at the level of a prelysosomal compartment. Here, it is of interest to note that evidence has been given recently to the acidity of prelysosomal/endocytic vacuoles (amphisomes), i.e.…”

Section: Discussionmentioning

confidence: 91%

Characterization of the swelling-induced alkalinization of endocytotic vesicles in fluorescein isothiocyanate-dextran-loaded rat hepatocytes

Schreiber

Häussinger

1995

Biochemical Journal

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Short-term cultivated rat hepatocytes were allowed to endocytose fluorescein isothiocyanate (FITC)-coupled dextran and the apparent vesicular pH (pHves) was measured by single-cell fluorescence. After 2 h of exposure to FITC-dextran, the apparent pH in the vesicular compartments accessible to endocytosed FITC-dextran was 6.01 +/- 0.05 (n = 39) in normo-osmotic media. Hypo-osmotic exposure increased, whereas hyper-osmotic exposure decreased apparent pHves. by 0.18 +/- 0.02 (n = 26) and 0.12 +/- 0.01 (n = 23) respectively. Incubation of the cells with unlabelled dextran for 2h before a 2-h FITC-dextran exposure had no effect on apparent pHves and its osmosensitivity. When, however, hepatocytes were exposed to unlabelled dextran for 5 h after a 2 h exposure to FITC-dextran, in order to allow transport of endocytosed FITC-dextran to late endocytotic/lysosomal compartments, apparent pHves. decreased to 5.38 +/- 0.04 (n = 12) and the apparent pH in the vesicular compartment containing the dye was no longer sensitive to aniso-osmotic exposure. These findings indicate that the osomosensitivity of pHves. is apparently restricted to early endocytotic compartments. Aniso-osmotic regulation of apparent pHves. in freshly FITC-loaded hepatocytes was not accompanied by aniso-osmolarity-induced changes of the cytosolic free calcium concentration, and neither vasopressin nor extracellular ATP, which provoked a marked Ca2+ signal, affected apparent pHves. Dibutyryl-cyclic AMP (cAMP) or vanadate (0.5 mmol/l) were without effect on apparent pHves. and its osmosensitivity. However, pertussis toxin-treatment or genistein (but not daidzein) or the erbstatin analogue methyl 2,5-dihydroxycinnamate fully abolished the osmo-sensitivity of apparent pHves., but did not affect apparent pHves. It is concluded that regulation of pHves. by cell volume occurs in early endocytotic compartments, but probably not in lysosomes, and is mediated by a G-protein and tyrosine kinase-dependent, but Ca2+- and cAMP-independent mechanism.

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“…Osmotic cell shrinkage is followed by acidification of endosomal vesicles [6] with subsequent activation of vesicular acidic sphingomyelinase and ceramide formation [5]. Hyperosmotic shock further triggers the generation of reactive oxygen species (ROS) by NADPH oxidase, an effect again requiring ceramide [5].…”

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confidence: 99%