Models of depressed hepatic mrp2 activity reveal bromosulphophthalein-sensitive passive K+ flux

2002 ◽  
Vol 80 (12) ◽  
pp. 1167-1172 ◽  
Author(s):  
Qin Li ◽  
M Martha Briggs ◽  
Doris Folkens ◽  
Ceredwyn E Hill
Keyword(s):  
Bile Acid ◽  
Rat Liver ◽  
Organic Anion ◽  
Isolated Hepatocytes ◽  
Early Event ◽  
Female Rat ◽  
Wild Type ◽  
Rat Livers ◽  
Gender Specific ◽  
Secretory Capacity

Bile acid independent flow composes up to 40% of hepatic bile secretory capacity. Apical (canalicular) efflux of non-bile-acid organic anions provides the major osmotic driving force for bile acid independent flow. Organic anion accumulation in the hepatocyte is accompanied by increases in both K+ conductance in isolated hepatocytes and passive K+ flux in the perfused rat liver, which are indicative of K+ channel activation. We used two models of disrupted canalicular anion transport to test whether organic anion stimulated K+ efflux occurs independently of anion excretion. In both wild type (wt) and mrp2 mutant (transport minus, tr–) rat liver, bromosulfophthalein (BSP; 0.5mM) caused a reversible increase in K+ flux that (i) was outwardly directed with low external K+ and (ii) depended upon the electrochemical potential for K+. K+ efflux from wt livers of both sexes was about 1.5 times larger than that from tr– livers. Further, K+ release from female rat livers was about three times higher than that from male livers, independent of phenotype. Two transcripts of the rat hepatocyte K+ channel (Kir4.2) were expressed in hepatocytes of all rats. The results demonstrate that BSP stimulates basolateral (sinusoidal) K+ channels independently of its canalicular excretion, revealing an early event in BAIF and suggesting that Kir4.2 may mediate BSP-sensitive K+ flux.Key words: liver, GY, gender-specific, male, female, transport minus, Kir4.2.

scholarly journals Effect of antisense oligonucleotides on the expression of hepatocellular bile acid and organic anion uptake systems in Xenopus laevis oocytes

1996 ◽  
Vol 316 (3) ◽  
pp. 901-904 ◽  
Author(s):  
Bruno HAGENBUCH ◽  
Bruce F. SCHARSCHMIDT ◽  
Peter J. MEIER
Keyword(s):  
Bile Acid ◽  
Xenopus Laevis ◽  
Rat Liver ◽  
Antisense Oligonucleotide ◽  
Antisense Oligonucleotides ◽  
Organic Anion ◽  
Xenopus Laevis Oocytes ◽  
Acid Uptake ◽  
Uptake System ◽  
Anion Uptake

A Na+-dependent bile acid (Na+/taurocholate co-transporting polypeptide; Ntcp) and a Na+-independent bromosulphophthalein (BSP)/bile acid uptake system (organic-anion-transporting polypeptide; oatp) have been cloned from rat liver by using functional expression cloning in Xenopus laevis oocytes. To evaluate the extent to which these cloned transporters could account for overall hepatic bile acid and BSP uptake, we used antisense oligonucleotides to inhibit the expression of Ntcp and oatp in Xenopus laevis oocytes injected with total rat liver mRNA. An Ntcp-specific antisense oligonucleotide co-injected with total rat liver mRNA blocked the expression of Na+-dependent taurocholate uptake by approx. 95%. In contrast, an oatp-specific antisense oligonucleotide when co-injected with total rat liver mRNA had no effect on the expression of Na+-dependent taurocholate uptake, but it blocked Na+-independent uptake of taurocholate by approx. 80% and of BSP by 50%. Assuming similar expression of hepatocellular bile acid and organic anion transporters in Xenopus laevis oocytes, these results indicate that Ntcp and oatp respectively represent the major, if not the only, Na+-dependent and Na+-independent taurocholate uptake systems in rat liver. By contrast, the cloned oatp accounts for only half of BSP transport, suggesting that there must be additional, non-bile acid transporting organic anion uptake systems in rat liver.

Nifedipine modulation of biliary GSH and GSSG/ conjugate efflux in normal and regenerating rat liver

2001 ◽  
Vol 281 (1) ◽  
pp. G85-G94 ◽  
Author(s):  
Bo Yang ◽  
Ceredwyn E. Hill
Keyword(s):  
Bile Acid ◽  
Sodium Nitroprusside ◽  
Rat Liver ◽  
Driving Force ◽  
Bile Flow ◽  
Organic Anion ◽  
High Capacity ◽  
Perfused Rat Liver ◽  
High Affinity ◽  
Glutathione Conjugate Transport

Canalicular glutathione secretion provides the major driving force for bile acid-independent bile flow (BAIF), although the pathways involved are not established. The hypothesis that GSH efflux proceeds by a route functionally distinct from the high-affinity, low-capacity, mrp2-mediated pathway was tested by using perfused rat liver and three choleretic compounds that modify biliary secretion of GSH (the dihydropyridine nifedipine and organic anion probenecid) or GSSG [sodium nitroprusside (SNP)]. Whereas nifedipine (30 μM) stimulated GSH secretion and blocked SNP-stimulated GSSG efflux and choleresis, SNP (1 mM) was ineffective against nifedipine-stimulated GSH efflux or BAIF, suggesting that most GSSG exits through a GSH-inhibitable path independent of high-affinity GSSG/glutathione conjugate transport. Three observations support this proposal. SNP, but not nifedipine, significantly inhibited bromosulfophthalein (BSP, 1 μM) excretion. Probenecid (1 mM) blocked resting or nifedipine-stimulated GSH secretion but only weakly inhibited BSP excretion. Glutathione, but not BSP, efflux capacity was reduced following partial hepatectomy. We suggest GSH efflux is mediated by a high-capacity organic anion pathway capable of GSSG transport when its high-affinity route is saturated.

Mechanism of bile acid facilitation of biliary protoporphyrin excretion in rat liver

1995 ◽  
Vol 268 (5) ◽  
pp. G754-G763 ◽  
Author(s):  
M. M. Berenson ◽  
M. Y. el-Mir ◽  
L. K. Zhang
Keyword(s):  
Bile Acid ◽  
Bile Acids ◽  
Intracellular Transport ◽  
Organic Anion ◽  
Anion Transport ◽  
Organic Anion Transport ◽  
Canalicular Membrane ◽  
Rat Livers ◽  
Eisai Hyperbilirubinemic Rat

The mechanism(s) by which bile acids increase biliary protoporphyrin excretion was characterized using perfused rat livers. We determined 1) relationships between biliary bile acids, phospholipid, and protoporphyrin, using rapid kinetic analyses; 2) protoporphyrin excretion in livers with defective canalicular multispecific organic anion transport; 3) effects of intracellular vesicular transport inhibition with colchicine and monensin; and 4) the role of luminal bile acids, using retrograde intrabiliary taurocholate injections. Biliary protoporphyrin excretion peaked with phospholipid excretion 14-18 min after loading. Protoporphyrin excretion induced by taurocholate was not related to effects on intracellular transport, including colchicine- and monensin-inhibitable vesicular systems. Eisai hyperbilirubinemic rat livers excreted protoporphyrin similarly to controls. Retrograde intrabiliary taurocholate injections increased protoporphyrin output. Collectively, these data suggest that 1) intracellular protoporphyrin transport is mediated by nonvesicular carriers targeted to the canalicular membrane, and 2) bile acid facilitates protoporphyrin translocation into bile in the same manner it effects phospholipid excretion.

scholarly journals Expression of c-Ki-ras, c-Ha-ras, and c-myc in specific cell types during hepatocarcinogenesis.

1985 ◽  
Vol 5 (4) ◽  
pp. 780-786 ◽  
Author(s):  
P Yaswen ◽  
M Goyette ◽  
P R Shank ◽  
N Fausto
Keyword(s):  
Rat Liver ◽  
Cell Types ◽  
Isolated Hepatocytes ◽  
Specific Cell ◽  
Oval Cells ◽  
Deficient Diet ◽  
Adult Rat ◽  
Fetal Rat ◽  
Fetal Rat Liver ◽  
Rat Livers

We examined the expression of six proto-oncogenes in (i) whole rat liver and isolated liver cell populations during the course of hepatocarcinogenesis induced by a choline-deficient diet containing 0.1% ethionine and (ii) fetal rat liver at different stages of development. The abundance of c-Ki-ras, c-Ha-ras, and c-myc transcripts in polysomal polyadenylated RNA from liver cells increased by 2 weeks after the start of the carcinogenic diet. c-Ki-ras and c-myc expression remained elevated during the 35 weeks of the diet, whereas c-Ha-ras transcripts increased transiently. A primary tumor sampled at 35 weeks after the carcinogenic diet was started contained high levels of both c-Ki-ras and c-myc RNA. The abundance of c-src transcripts was unchanged throughout carcinogenesis; c-abl and c-mos transcripts were not detected in either preneoplastic or neoplastic livers. To determine which cell types within the liver contained proto-oncogene transcripts, we isolated hepatocytes, oval cells, and bile duct cells from normal and preneoplastic livers. The results indicate that proto-oncogenes are expressed differentially in these cell types during hepatocarcinogenesis and that the expression of c-Ki-ras and c-myc is high in oval cells throughout carcinogenesis. In developing livers, c-Ki-ras, c-Ha-ras, and c-myc transcript levels were high at 17 days of gestation but reached the low values characteristic of adult rat livers between 20 days of gestation and 3 days after birth.

Bile Acid Metabolism in Mammals. V. Studies on the Sex Difference in the Response of the Isolated Perfused Rat Liver to Chenodeoxycholic Acid

1973 ◽  
Vol 51 (6) ◽  
pp. 418-423 ◽  
Author(s):  
I. M. Yousef ◽  
R. Magnusson ◽  
V. M. Price ◽  
M. M. Fisher
Keyword(s):  
Bile Acid ◽  
Sex Difference ◽  
Rat Liver ◽  
Chenodeoxycholic Acid ◽  
Bile Acid Metabolism ◽  
Isolated Perfused Rat Liver ◽  
Base Line ◽  
Female Rat ◽  
Perfused Rat Liver ◽  
Perfusion Medium

The hepatic metabolism of chenodeoxycholic acid (CDCA) was studied using the isolated perfused rat liver technique. In 12 perfusions, six male and six female, 30 μmol of CDCA were added to the perfusion medium, and in 12 other perfusions, also six of each sex, 1 μmol of CDCA was added to the perfusion medium. The CDCA was added after 2 h of base-line perfusion and the bile acids of liver, plasma, and bile were analyzed by combined thin-layer and gas chromatography. In the 2 h of perfusion prior to the addition of exogenous CDCA there were sex differences in the kinetics of bile acid secretion in the bile and in the bile acid composition of that bile. Following the addition of CDCA to the perfusion medium the female liver was found to take up more CDCA from the perfusion medium, to store more CDCA, and to convert less CDCA to β-muricholic acid. It was documented that the toxicity of CDCA for the isolated perfused liver of the female rat is not due to α- or β-muricholic acid, the end products of CDCA metabolism in the rat. The relatively greater capacity of the male liver to convert potentially toxic CDCA to nontoxic β-muricholic acid may explain, at least in part, the observed sex difference in CDCA hepatotoxicity.

Amiloride and taurine inhibit cholate-induced HCO3(-)-rich choleresis in perfused rat livers

1990 ◽  
Vol 259 (3) ◽  
pp. G453-G461
Author(s):  
M. S. Anwer ◽  
J. M. Atkinson ◽  
P. Zimniak
Keyword(s):  
Bile Acid ◽  
Biliary Excretion ◽  
Bile Flow ◽  
Excretion Rate ◽  
Isolated Hepatocytes ◽  
Hepatic Uptake ◽  
Polar Compound ◽  
Biliary Reabsorption ◽  
Rat Livers ◽  
Primary Activation

Bile acid-induced HCO3(-)-rich choleresis may be due to primary activation of sinusoidal Na(+)-H+ exchange or to biliary reabsorption of unconjugated bile acid. To test these hypotheses, we studied the effect of cholate and taurocholate (TC) (infused at 10 mumol/min for 20 min) on net H+ efflux, biliary [HCO3-], and bile flow in perfused rat livers and on intracellular pH (pHi) in isolated hepatocytes. Cholate, but not TC, produced HCO3(-)-rich choleresis. Amiloride and taurine decreased cholate-induced choleresis and HCO3- excretion and biliary excretion of unconjugated cholate. Amiloride, but not taurine, decreased cholate-induced net H+ efflux. Both cholate and TC (200-750 microM) decreased pHi. Cholate was metabolized to a polar compound, most likely cholate glucuronide, in the presence of amiloride. These results are consistent with the hypothesis that the biliary reabsorption of unconjugated cholate may be involved in HCO3(-)-rich choleresis. Amiloride also inhibited net hepatic uptake and biliary excretion of cholate and TC without affecting hepatic content of bile acids. It is suggested that amiloride may decrease the maximal excretion rate of cholate and TC. Since cholate and TC induce amiloride-sensitive net H+ efflux and decrease pHi, it appears that cholate and TC activate Na(+)-H+ exchange indirectly by decreasing pHi.

scholarly journals Partial purification and properties of an enzyme from rat liver that catalyses the sulphation of l-tyrosyl derivatives

1970 ◽  
Vol 116 (5) ◽  
pp. 797-803 ◽  
Author(s):  
P. Mattock ◽  
J. G. Jones
Keyword(s):  
Methyl Ester ◽  
Rat Liver ◽  
Potent Inhibitor ◽  
Quantitative Difference ◽  
Partial Purification ◽  
Female Rat ◽  
Mixed Substrate ◽  
Partial Separation ◽  
Purification And Properties ◽  
Rat Livers

1. An enzyme that catalyses the transfer of sulphate from adenosine 3′-phosphate 5′[35S]-sulphatophosphate to l-tyrosine methyl ester and tyramine was purified approx. 70-fold from female rat livers. 2. The partially purified preparation is still contaminated with adenosine 3′-phosphate 5′-sulphatophosphate–phenol sulphotransferase (EC 2.8.2.1), but a partial separation of the two enzymes can be achieved by chromatography on columns of Sephadex G-200 and DEAE-Sephadex. 3. The enzyme responsible for the sulphation of l-tyrosine methyl ester and tyramine is activated by dithiothreitol, 2-mercaptoethanol and GSH, the degree of activation being more marked with preparations previously stored at 0 or -10°C. In contrast, the enzymic sulphation of p-nitrophenol is inhibited by all three thiols. Again, there is a quantitative difference in the degree of inhibition of the two enzymes by o-iodosobenzoate, p-chloromercuribenzoate, N-ethylmaleimide and iodoacetate. 4. Mixed-substrate experiments support the hypothesis that the enzyme responsible for the sulphation of l-tyrosine methyl ester and tyramine is separate from that responsible for the sulphation of p-nitrophenol. However, p-nitrophenol is a potent inhibitor of the sulphation of both tyrosyl derivatives whereas these latter compounds have no effect on the sulphation of p-nitrophenol.

Expression of c-Ki-ras, c-Ha-ras, and c-myc in specific cell types during hepatocarcinogenesis

1985 ◽  
Vol 5 (4) ◽  
pp. 780-786
Author(s):  
P Yaswen ◽  
M Goyette ◽  
P R Shank ◽  
N Fausto
Keyword(s):  
Rat Liver ◽  
Cell Types ◽  
Isolated Hepatocytes ◽  
Specific Cell ◽  
Oval Cells ◽  
Deficient Diet ◽  
Adult Rat ◽  
Fetal Rat ◽  
Fetal Rat Liver ◽  
Rat Livers

We examined the expression of six proto-oncogenes in (i) whole rat liver and isolated liver cell populations during the course of hepatocarcinogenesis induced by a choline-deficient diet containing 0.1% ethionine and (ii) fetal rat liver at different stages of development. The abundance of c-Ki-ras, c-Ha-ras, and c-myc transcripts in polysomal polyadenylated RNA from liver cells increased by 2 weeks after the start of the carcinogenic diet. c-Ki-ras and c-myc expression remained elevated during the 35 weeks of the diet, whereas c-Ha-ras transcripts increased transiently. A primary tumor sampled at 35 weeks after the carcinogenic diet was started contained high levels of both c-Ki-ras and c-myc RNA. The abundance of c-src transcripts was unchanged throughout carcinogenesis; c-abl and c-mos transcripts were not detected in either preneoplastic or neoplastic livers. To determine which cell types within the liver contained proto-oncogene transcripts, we isolated hepatocytes, oval cells, and bile duct cells from normal and preneoplastic livers. The results indicate that proto-oncogenes are expressed differentially in these cell types during hepatocarcinogenesis and that the expression of c-Ki-ras and c-myc is high in oval cells throughout carcinogenesis. In developing livers, c-Ki-ras, c-Ha-ras, and c-myc transcript levels were high at 17 days of gestation but reached the low values characteristic of adult rat livers between 20 days of gestation and 3 days after birth.

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