Release of osmolytes induced by phagocytosis and hormones in rat liver

Matthias Wettstein, Thorsten Peters-Regehr, Ralf Kubitz, Richard Fischer, Claudia Holneicher, Irmhild Mönnighoff, and Dieter Häussinger

Clinic for Gastroenterology, Hepatology, and Infectious Disease, Heinrich Heine University, 40255 Düsseldorf, Germany


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Betaine, taurine, and inositol participate as osmolytes in liver cell volume homeostasis and interfere with cell function. In this study we investigated whether osmolytes are also released from the intact liver independent of osmolarity changes. In the perfused rat liver, phagocytosis of carbon particles led to a four- to fivefold stimulation of taurine efflux into the effluent perfusate above basal release rates. This taurine release was inhibited by 70-80% by the anion exchange inhibitor DIDS or by pretreatment of the rats with gadolinium chloride. Administration of vasopressin, cAMP, extracellular ATP, and glucagon also increased release of betaine and/or taurine, whereas insulin, extracellular UTP, and adenosine were without effect. In isolated liver cells, it was shown that parenchymal cells and sinusoidal endothelial cells, but not Kupffer cells and hepatic stellate cells, release osmolytes upon hormone stimulation. This may be caused by a lack of hormone receptor expression in these cells, because single-cell fluorescence measurements revealed an increase of intracellular calcium concentration in response to vasopressin and glucagon in parenchymal cells and sinusoidal endothelial cells but not in Kupffer cells and hepatic stellate cells. The data show that Kupffer cells release osmolytes during phagocytosis via DIDS-sensitive anion channels. This mechanism may be used to compensate for the increase in cell volume induced by the ingestion of phagocytosable material. The physiological significance of hormone-induced osmolyte release remains to be evaluated.

liver cell volume homeostasis; betaine; taurine; osmoregulation


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

THE HEPATOCELLULAR HYDRATION state is an important determinant of metabolic liver function and gene expression (for review, see Refs. 9 and 10). Recently, it became clear that liver cells use osmolyte strategies and that osmolytes interfere with cell volume regulation and cell function. Organic osmolytes are compounds that are accumulated or released by the cells in response to hyperosmotic cell shrinkage or hyposmotic cell swelling, respectively, to maintain cell volume homeostasis. Osmolytes must be nonperturbing solutes that do not interfere with protein function even at high intracellular concentrations (3, 7, 28). Therefore, only a few classes of organic compounds, i.e., polyols (inositol, sorbitol), methylamines (betaine, alpha -glycerophosphocholine), and certain amino acids such as taurine have evolved as osmolytes in living cells. In mammals, osmolytes have been identified in astrocytes, renal medullary cells, and lens epithelia (14, 15, 32).

The various liver cell populations use different osmolytes (21, 23, 25, 26, 30). In the intact perfused rat liver, hyposmolar exposure induces a rapid release of betaine and taurine into the effluent perfusate (23, 30). In rat liver parenchymal cells (PC) and H4IIE rat hepatoma cells, hyperosmotic exposure leads within several hours to an increase in taurine transporter (TAUT) mRNA levels and an intracellular accumulation of taurine (23). In contrast, hyposmotic exposure of PC results in an immediate release of taurine, presumably via volume-regulated anion channels. Hyperosmotic exposure of cultured Kupffer cells (KC) and sinusoidal endothelial cells (SEC) induces betaine and myo-inositol transporters (BGT1 and SMIT, respectively), whereas TAUT and intracellular taurine levels are already high under normosmolar conditions (21, 25, 26, 30). The results obtained in these cells suggest that taurine is the major osmolyte released in response to hyposmotic stress, whereas betaine and myo-inositol are accumulated in response to hyperosmolarity.

Recent evidence suggests that osmolytes not only play a role in liver cell volume regulation but also interfere with cell function. KC function is regulated by changes of ambient osmolarity: endotoxin-induced prostaglandin E2, prostaglandin D2, and thromboxane B2 formation and cyclooxygenase-2 expression are stimulated 7- to 10-fold when ambient osmolarity increases from 300 to 350 mosmol/l (31). Tumor necrosis factor-alpha (TNF-alpha ) and interleukin-6 production and phagocytosis by isolated KC are also sensitive to osmolarity changes (24, 29). Osmolarity effects on prostanoid synthesis, cyclooxygenase-2 expression, phagocytosis, and TNF-alpha production can be suppressed by betaine (22, 24, 29, 30). Taurine and betaine in physiological concentrations are protective in ischemia-reoxygenation injury in the perfused rat liver (27). This effect seems to be caused by an inhibitory effect of these osmolytes on KC activation, but direct effects on PC may also play a role. For example, taurine restores the heat shock-induced induction of the heat shock protein HSP 70 in isolated rat PC, which is almost abolished in hyperosmotic media (12).

In view of this role of osmolytes in cell function, the present study addresses the interesting question of whether osmolyte status in liver is also regulated by nonosmotic effectors. The data show that hormones and phagocytotic stimuli interfere with the osmolyte content of different liver cell types, suggestive of another mechanism of regulation of cell function.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Materials. [Methyl-14C]betaine (48.1 mCi/mmol) was synthesized by DuPont NEN (Bad Homburg, Germany). [3H]taurine (24 Ci/mmol) and myo-[3H]inositol (22.3 Ci/mmol) were also obtained from DuPont NEN. cAMP, ATP, UTP, and adenosine were from Boehringer Mannheim (Mannheim, Germany). Fura 2-AM and Oregon Green 488 BAPTA 1-AM were from Molecular Probes (Eugene, OR). All other chemicals were from Sigma (Deisenhofen, Germany) and Merck (Darmstadt, Germany).

Rat liver perfusion. Male Wistar rats (120- to 180-g body wt) with free access to a stock diet were raised in the local institute for laboratory animals and maintained according to local ethical guidelines. Livers were isolated and perfused as described previously (19) in a blood-free, nonrecirculating system with bicarbonate-buffered Krebs-Henseleit saline supplemented with 2.1 mmol/l lactate and 0.3 mmol/l pyruvate. The influent K+ concentration was 5.9 mmol/l. Betaine and taurine (Sigma) were dissolved in the perfusion buffer. Perfusate flow was 3.5-4 ml · g liver-1 · min-1. The perfusate was equilibrated with O2-CO2 (95:5 vol/vol), yielding a PO2 of 523 ± 22 mmHg (n = 4) in the influent as determined with a blood gas analyzer. The temperature was 37°C. Osmolarity of the perfusion fluid was 305 mosmol/l. K+ concentration in the effluent perfusate was monitored with a K+-sensitive electrode (Radiometer, Willich, Germany), and portal pressure was measured continuously with a pressure transducer.

The rat livers were labeled with 25 µCi of [3H]taurine and 25 µCi of [14C]betaine added to the perfusate at the beginning of the perfusion experiments for 20 min. In other experiments, rats were prelabeled by intraperitoneal injection of 25 µCi of myo-[3H]inositol. In inhibitor studies, DIDS dissolved in dimethyl sulfoxide was added with a syringe and a precision micropump (flow rate 0.05 ml/min), yielding an influent concentration of 100 µmol/l. Dimethyl sulfoxide alone did not interfere with osmolyte release. Hormones were dissolved in perfusion buffer and added to the influent perfusate using micropumps. Gadolinium pretreatment of rats was performed by injection in the rat tail vein of 2 mg of GdCl3 dissolved in 1 ml of 0.9% NaCl 40 and 16 h before liver isolation for perfusion.

Liver cell isolation and determination of osmolyte efflux. KC and SEC were isolated from male Wistar rats by collagenase-pronase perfusion and separated by a single Nycodenz gradient and centrifugal elutriation (5). Cells were cultured in RPMI 1640 medium supplemented with 10% heat-inactivated FCS for 24 h (SEC) or 48 h (KC). Thereafter, the cultivation was continued in RPMI 1640 medium supplemented with 1% FCS for an additional 6 h.

Liver PC were prepared from livers of male Wistar rats by collagenase perfusion as described previously (13). Cells were cultivated in DMEM (Biochrom, Berlin, Germany) containing 5 mmol/l glucose and 10% FCS for 24 h. Thereafter, the cultivation was continued in the same medium without FCS for an additional 6 h. Cell cultures were incubated at 37°C in an atmosphere of 95% air-5% CO2.

Hepatic stellate cells (HSC) from 1-year-old male Sprague-Dawley rats were prepared by collagenase-pronase perfusion and isolated by a single Nycodenz gradient as described elsewhere (18). The cells were maintained in 1 ml DMEM containing 4 mmol/l L-glutamine, 25 mmol/l glucose, and 10% heat-inactivated FCS. The cells were cultured for 48 h in a humidified atmosphere of 5% CO2-95% air at 37°C.

For studies of osmolyte efflux, KC, SEC, HSC, and PC were preincubated 6 h in normosmotic medium (305 mosmol/l). KC and SEC were incubated in 12-well dishes (~1 × 106 cells/well; Becton Dickinson, Heidelberg, Germany), PC in 6-well dishes (106 cells/well), and HSC in 12-well dishes (0.2 × 106 cells/well). Thereafter, [14C]betaine or [3H]taurine (100 µmol/l, 0.5 µCi/ml) was added to load the cells with radioisotope. After a loading period of 4 h, cells were rinsed three times with normosmotic medium (305 mosmol/l). The cells were then incubated in osmolyte-free hyposmotic (205 mosmol/l) or normosmotic medium with or without glucagon, vasopressin, or cAMP for 1 h as indicated. Thereafter, the medium was collected and cells were harvested with 1 ml 0.1% SDS. Radioactivity in the supernatant was measured by scintillation counting and expressed as a percentage of total radioactivity contained in cells and supernatant.

Assays. Carbon uptake by the perfused liver was determined as described (4). In brief, Pelikan black ink no. 17 was dialyzed against distilled water for 48 h and added to the influent perfusate, yielding an absorbance at 578 nm of ~1.2, corresponding to a carbon concentration of ~0.5 mg/ml. Carbon uptake was calculated from Delta A578 between influent and effluent perfusate. Steady-state uptake rates were reached within 5-10 min. One-milliliter samples of the effluent perfusate were collected every minute and counted for radioactivity. During carbon administration samples were centrifuged before counting because carbon interfered with scintillation counting. Additional 10-ml perfusate samples were collected during the first minutes of hormone or carbon administration and evaporated to dryness in a Speed-Vac concentrator (Uni-Equip, Martinsried, Germany). The samples were resuspended in 200 µl of water, filtered through Millipore HV4 microfilters (Millipore, Eschborn, Germany), and subjected to HPLC analysis as described previously (24) using a Perkin-Elmer Pecosphere-3CSi column (4.6 × 83 mm, 5-µm particles). The mobile phase consisted of solvent A (acetonitrile-ethanol-acetic acid-1.0 mmol/l ammonium acetate-water-0.1 mmol/l sodium phosphate, 800:68:2:3:127:10 by volume) and solvent B (acetonitrile-ethanol-acetic acid-1.0 mmol/l ammonium acetate-water-0.1 mmol/l sodium phosphate, 400:68:44:88:400:10 by volume). One hundred percent solvent A was delivered for 8 min, followed by a concave gradient to one hundred percent solvent B over 10 min; one hundred percent solvent B was maintained for another 10 min. The flow rate was 1.5 ml/min. Radioactivity in the HPLC effluent was continuously monitored with a Ramona 5LS radioactivity monitor (Raytest, Straubenhardt, Germany). Taurine was also measured by conventional amino acid analysis with a BioChrom20 analyzer (Pharmacia, Freiburg, Germany). Sorbitol was measured enzymatically as described in Ref. 2.

Measurement of cytosolic free Ca2+ concentration. For cytosolic free Ca2+ concentration ([Ca2+]i) measurements, cells were cultured on uncoated glass coverslips (KC) or slips coated with collagen I (SEC), collagen VII (PC), or DMEM + 10% FCS (HSC). PC, SEC, KC, and HSC were investigated 4-8, 24, 48, and 24-48 h after isolation, respectively. Cells were washed with Krebs-Henseleit buffer (KHB) containing 6 mmol/l glucose (37°C, 95% O2-5% CO2, pH 7.4) 1 h before [Ca2+]i measurement. PC, KC, and SEC were loaded with 5 µmol/l fura 2-AM for 30 min before the measurement. After the loading period, the coverslips were mounted in a perfusion chamber on an inverted fluorescence microscope (Zeiss, Oberkochem, Germany) and continuously superfused with KHB (37°C, 95% O2-5% CO2, pH 7.4) at a rate of 10 ml/min. Single cells loaded with fura 2 were alternately excited at 340 and 380 nm, respectively, at a rate of 10 Hz with the use of a high-speed filter wheel. Emission was measured at 480-520 nm with a photon counting tube (Hamamatsu H3460-04, Hersching, Germany). Autofluorescence was assessed in unloaded cells and accounted for <5% of the signal measured in fura 2-loaded cells. It was substracted, and [Ca2+]i was calculated from the fluorescence ratio of 380 to 340 nm according to the method described in Ref. 6 using 2 µmol/l of ionomycin for equilibration of intra- and extracellular Ca2+ concentration in calibration experiments. The dissociation constant for the fura 2-Ca2+ complex was taken as 224 nmol/l. Cytosolic calcium measurements with fura 2 were more difficult in SEC than in PC and KC because of an unfavorable nucleus-plasma relation. A major part of fura 2 accumulated in the nuclei, which do not participate in the cytosolic calcium changes, and the fluorescence signal was therefore more difficult to detect than in the other cell lines.

Because of autofluorescence at 340/380 nm, HSC were loaded with 5 µmol/l of the Ca2+-sensitive dye Oregon Green 488 BAPTA 1-AM (17). HSC were alternately excited at 440 and 488 nm; emission was measured at 515-565 nm. The measurements are expressed as photon counts per second at 488 nm; the time resolution was 10 Hz. The autofluorescence was substracted and was <5% of the total fluorescence of the dye-loaded cells. A semiquantitative analysis of the measurements was performed by dividing the maximal photon count during stimulation by the photon count just before stimulation. One cell per coverslip was investigated, and each cell type was tested in cells of at least three different preparations. Stimulation of [Ca2+]i by UTP in all four cell types was taken as proof of viability of the measurements.

Statistics. Values are expressed as means ± SE. Statistical significance was determined using Student's t-test.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Osmolyte release during phagocytosis of carbon particles in perfused rat liver. Livers were prelabeled with [3H]taurine and [14C]betaine for 20 min at the beginning of a liver perfusion experiment. After the prelabeling period there was a basal release of tritium- and 14C-associated radioactivity into the effluent perfusate. When carbon was added to the influent perfusate, a steady-state carbon uptake rate was reached within 10 min (Fig. 1). After carbon administration there was a marked increase of tritium-associated radioactivity in the effluent perfusate with a maximum after ~10 min. In HPLC analysis, this radioactivity coeluted with taurine standards. Amino acid analysis of the effluent perfusate confirmed an increase of taurine concentration in the effluent perfusate from a basal level of 0.7 ± 0.1 µmol/l to 1.2 ± 0.2 µmol/l (n = 4) after 4 min of carbon administration. In contrast to taurine, no stimulation of betaine release into the perfusate was induced by carbon phagocytosis (Fig. 1). In a different series of experiments, rats were prelabeled intraperitoneally with myo-[3H]inositol 12 h before isolation of livers for perfusion. In these livers, carbon phagocytosis only induced a minor release of radioactivity (Fig. 2). There was also no release of sorbitol detectable before and during phagocytosis of carbon (not shown). Thus in the perfused rat liver carbon phagocytosis induces a release of taurine from the liver but not of betaine and sorbitol and only minor amounts of inositol.


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Fig. 1.   Carbon phagocytosis-induced release of taurine into effluent in perfused rat liver. Livers were prelabeled with 25 µCi [3H]taurine and [14C]betaine during first 20 min of perfusion. Values are means ± SE (n = 4 livers).



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Fig. 2.   Carbon phagocytosis-induced release of myo-inositol into effluent in perfused rat liver. Rats were prelabeled with 25 µCi of myo-[3H]inositol 12 h before liver isolation for perfusion. Values are means ± SE (n = 3 livers).

Intravenous injection of gadolinium chloride at a dose of 10 mg/kg body weight is known to inactivate >80% of the KC in situ (1, 8). Phagocytosis-induced taurine release was largely diminished in rats pretreated with gadolinium chloride (Fig. 3). Taurine release was also decreased in the presence of the anion exchanger inhibitor DIDS (Fig. 4). These data suggest that taurine efflux may occur predominantly from KC, presumably via volume-sensitive anion channels.


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Fig. 3.   Effect of gadolinium chloride pretreatment on carbon phagocytosis-induced release of taurine in perfused rat liver. Livers were prelabeled with 25 µCi of [3H]taurine during first 20 min of perfusion. Gadolinium pretreatment of rats was performed by intravenous injection of 2 mg GdCl3 dissolved in 1 ml of 0.9% NaCl 40 and 16 h before liver isolation for perfusion. Values are means ± SE (n = 3 livers).



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Fig. 4.   Effect of DIDS on carbon phagocytosis-induced release of taurine in perfused rat liver. Livers were prelabeled with 25 µCi of [3H]taurine during first 20 min of perfusion. DIDS was added after prelabeling period and was present throughout following experiment. Values are means ± SE (n = 3 livers).

Betaine and taurine release induced by hormones. Because many hormones have major effects on cell volume and some of their metabolic effects are mediated through cell volume changes (11), the effect of hormones on release of betaine and taurine was investigated. In the perfused liver, betaine release was induced by glucagon and the combination of vasopressin and cAMP (Table 1, Figs. 5 and 6). Taurine release was induced by vasopressin, ATP, and vasopressin plus cAMP. The combination of vasopressin and cAMP had the strongest effect, with a maximum increase of taurine release of more than threefold compared with the basal release. It should be noted that these hormones caused a decrease of liver cell hydration and stimulated osmolyte release, indicating that osmolyte shifts were not the consequence of cell volume changes. It appears rather that hormone-induced osmolyte release contributes to the cell shrinkage in response to hormonal stimulation. Interestingly, glucagon stimulated betaine efflux, whereas cAMP did not, indicating that the glucagon effect is independent of cAMP increase. However, cAMP had a permissive effect on the osmolyte release induced by vasopressin.

                              
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Table 1.   Osmolyte release induced by hormones in perfused rat liver



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Fig. 5.   Release of betaine and taurine induced by vasopressin and cAMP in perfused rat liver. Livers were prelabeled with 25 µCi of [3H]taurine and [14C]betaine during first 20 min of perfusion. Values are expressed as percentage of basal radioactivity release during last 10 min before hormone administration and are means ± SE (n = 3 livers).



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Fig. 6.   Release of betaine induced by glucagon in perfused rat liver. Livers were prelabeled with 25 µCi [14C]betaine during first 20 min of perfusion. Values are expressed as percentage of basal radioactivity release during last 10 min before hormone administration and are means ± SE (n = 3 livers).

To clarify which subset of liver cells releases osmolytes in response to hormones, isolated rat liver cells were loaded with [3H]taurine and [14C]betaine and then incubated in normosmolar or hyposmolar buffer or in normosmolar buffer containing hormones. In PC, SEC, HSC, and KC, incubation in hyposmolar medium (205 mosmol/l) stimulated release of betaine and taurine from all cell types compared with controls with incubation in normosmolar buffer (Table 2). Vasopressin plus cAMP and glucagon also stimulated betaine and taurine release from PC and SEC. In contrast, no significant stimulation of betaine or taurine release was seen in KC and HSC. These data show a differential response of liver cell subpopulations with respect to hormone-induced osmolyte release. However, there were some differences between the results obtained in the perfused rat liver and isolated liver cells. In isolated PC and SEC, glucagon strongly stimulated taurine and betaine release (Table 2), whereas in the perfused liver only a minor but significant betaine release and no taurine release were observed (Table 1). The shorter period of hormone administration in the perfusion experiments compared with cell incubations does not explain these findings, because most of the glucagon-induced radioactivity release occurred during the first 30 min of cell incubation (data not shown). Thus the data indicate that the responsiveness to hormones concerning osmolyte release may be different in the intact organ and isolated cells.

                              
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Table 2.   Osmolyte release induced by hyposmolarity and hormones in isolated rat liver cells

Measurement of [Ca2+]i in response to hormones in isolated liver cells. In PC, high concentrations of vasopressin (100 nmol/l) and glucagon (500 nmol/l) induced a rapid increase of [Ca2+]i that outlasted the presence of the hormone (Fig. 7, Table 3). In SEC, both hormones induced a slight increase in [Ca2+]i of 19 ± 18 nmol/l (vasopressin, n = 17) and 41 ± 14 nmol/l (glucagon, n = 10) above basal [Ca2+]i, whereas UTP increased [Ca2+]i by 138 ± 21 nmol/l. In contrast to PC and SEC, no significant increase of [Ca2+]i in response to vasopressin and glucagon was detectable in KC and HSC, where a [Ca2+]i signal in these cells occurred in response to extracellular UTP (Table 3). The results indicate that KC and HSC have no receptors for glucagon and vasopressin that are linked to calcium-mobilizing devices. The absence of receptors for these hormones may also explain the lack of hormone-induced osmolyte release in these cells.


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Fig. 7.   Measurement of cytosolic free-Ca2+-concentration ([Ca2+]i) in response to vasopressin, glucagon, and extracellular UTP in isolated single liver parenchymal cells (PC; top) and Kupffer cells (KC; bottom). [Ca2+]i was measured in fura 2-loaded PC and KC as described in MATERIALS AND METHODS. Representative of 5-8 different cell measurements.


                              
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Table 3.   Effect of hormones on [Ca2+]i in isolated single liver cells


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Phagocytosis is an important function of KC. When colloidal carbon is infused into rat livers, KC take up the major part, whereas a minor part is phagocytosed by sinusoidal endothelial cells (4). Phagocytosis of latex particles by KC is stimulated by hyposmolar incubation and decreased in hyperosmolarity (24). After preincubation in hyperosmotic medium to stimulate osmolyte uptake into isolated KC, addition of latex particles induced the release of betaine and taurine into the supernatant (24, 25). Latex particles did not affect mRNA levels of the betaine transporter BGT1 and the taurine transporter TAUT (25).

In the present study we investigated whether phagocytosis also leads to release of osmolytes in the intact liver. During phagocytosis of carbon particles an up to fourfold increase of taurine release into the effluent perfusate was observed, whereas there was no release of other osmolytes such as betaine and sorbitol and only minor release of inositol (Figs. 1 and 2). The taurine release was sensitive to the anion exchanger inhibitor DIDS, showing that volume-sensitive anion channels may be involved in the phagocytosis-induced osmolyte release. Pretreatment of rats with gadolinium chloride, which inactivates KC (1, 8), also decreased phagocytosis-induced taurine release. The physiological role of the taurine release may be that it counteracts the volume increase of the intrasinusoidal KC during phagocytosis. Thus obstruction of the sinusoids and impairment of hepatic blood flow may be prevented. The data are also in line with other observations in different liver cell populations that taurine is the most important osmolyte under normosmolar conditions, whereas betaine and inositol are accumulated during hyperosmotic exposure (26).

In liver cells many hormones interfere with ion transport systems in the plasma membrane, leading to cell volume changes, and part of the hormone action is explained by their effect on the cellular hydration state (9-11). For example, glucagon causes cell shrinkage, whereas insulin induces cell swelling. After prelabeling of livers with [3H]taurine and [14C]betaine, a hormone-induced osmolyte efflux could be demonstrated and vasopressin was most effective. In isolated cells it was shown that these hormones stimulate betaine and taurine release from PC and SEC but not from KC and HSC, demonstrating a differential response of liver cell subpopulations (Table 2). This may be explained by a lack of vasopressin and glucagon receptor expression in KC and HSC, because increases of [Ca2+]i after vasopressin and glucagon stimulation were only seen in PC and SEC but not in KC and HSC (Table 3, Fig. 7).

Recently, hepatic osmolyte release was also shown to be induced by perivascular nerve stimulation that could be mimicked by phenylephrine (20). In this case, osmolyte release may be a volume regulatory mechanism secondary to cell swelling as nerve stimulation increases liver cell volume. The hormones reported here to induce betaine and/or taurine release all cause liver cell shrinkage. Thus these hormones are likely to activate anion channels in the cell membranes, thereby leading to osmolyte efflux. The osmolyte release induced by hormones was not enough to account for a major part of the total liver cell volume changes induced by these hormones. However, hormone-induced release of osmolytes may influence cell hydration in a subset of liver cells, thereby modulating cell function.


    ACKNOWLEDGEMENTS

This study was supported by the Deutsche Forschungsgemeinschaft through Grant We 1936/1-3 and the Leibniz Program.


    FOOTNOTES

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: D. Häussinger, Klinik für Gastroenterologie, Hepatologie und Infektiologie Heinrich-Heine-Universität, Moorenstrasse 5, 40225 Düsseldorf, Germany (E-mail: wettstein{at}med.uni-duesseldorf.de).

Received 26 July 1999; accepted in final form 26 October 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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Am J Physiol Gastroint Liver Physiol 278(2):G227-G233
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