M. G. Raeder

The origin of and subcellular mechanisms causing pancreatic bicarbonate secretion

In recent years, there has been a rapid growth in knowledge about the subcellular mechanisms involved in pancreatic ductal secretion of bicarbonate. The mechanisms governing anion transport across the luminal membrane of duct cells have been well characterized. Evidence suggests that the cystic fibrosis transmembrane conductance regulator is a cyclic adenosine monophosphate-regulated Cl- conductance in the luminal membrane that plays a pivotal role in ductal bicarbonate secretion by recirculating the Cl- imported into duct cells through Cl(-)-HCO3- exchange. The mechanisms governing ion transfer across the basolateral plasma membrane of duct cells are less well defined. There is some evidence suggesting that secretin may cause exocytotic insertion of proton pumps into the basolateral plasma membrane. Once inserted into the plasma membrane, proton pumps could engage in primary active electrogenic H+ ion transport to interstitial tissue while secondary active HCO3- secretion occurs over the luminal membrane through Cl(-)-HCO3- exchangers coupled in parallel with the cystic fibrosis transmembrane conductance regulator. These and other subcellular phenomena related to ductal secretory function are reviewed.

Multiple inflammatory-, tissue remodelling- and fibrosis genes are differentially transcribed in the livers of Abcb4 (−/ − ) mice harbouring chronic cholangitis

Objective. Abcb4 (−/−) mice secrete phosphatidylcholine-free, cytotoxic bile and develop chronic cholangitis. The aim of this study was to identify differentially transcribed genes whose products contribute to the liver tissue pathology during this disease. Material and methods. Hepatic gene transcription was measured in 3-, 6-, 9- and 20-week-old Abcb4 (−/−) mice (FVB.129P2-abcb4tm1Bor/J) using cDNA microarrays, with FVB/NJ Abcb4 (+/+) mice serving as controls. Focus was on inflammatory-, remodelling- and fibrosis genes. Marked differential transcription of inflammatory-, tissue remodelling- and fibrosis genes found by cDNA microarrays was verified by real-time polymerase chain reaction (PCR). Liver pathology was quantified by histopathology scoring. Results. Transcription of clade A3 Serpin genes showed early, marked down-regulation. The chemokine genes Ccl2, Ccl20 and Cxcl10 were markedly up-regulated. Tissue remodelling- and fibrosis genes exhibiting markedly up-regulated transcription included: Ctgf, Elf3, Lgals3, Mmp12, Mmp15, Spp1, Loxl2, Pdgfa, Pdgfrb, Sparc, Tgfb1, Tgfb2, Tgfbi, Tgfbr2 and Col1a1, Col1a2, Col2a1, Col3a1, Col4a1 genes. Microarray-based recordings of differential gene transcription of the majority of these genes harmonized with the liver histopathology score. Thus, cDNA microarray-based analysis showed increasing differential transcription of several inflammatory-, tissue remodelling- and fibrosis genes during the first 9 weeks of disease and a tendency towards differential transcription to stabilize at an elevated level from 9 to 20 weeks of disease. Conclusions. Multiple genes regulating inflammation, tissue remodelling and fibrosis not previously linked to Abcb4 (−/−) cholangitis are identified as being differentially transcribed in Abcb4 (−/−) livers, where they contribute to the pathogenesis of liver tissue pathology.

Effect of Acetazolamide on Glomerulotubular Balance and Renal Metabolic Rate

Mathisen, O., Raeder, M., Sejersted, O. M. & Kiil, F. Effect of Acetazolamide on Glomerulotubular Balance and Renal Metabolic Rate. Scand. J. clin. Lab. Invest. 36, 617–625, 1976.Glomerulotubular balance, defined as proportionality between filtered and re-absorbed sodium during inhibition of sodium reabsorption in the thick ascending limb of Henles loop (diluting segment), was examined in anaesthetized dogs by gradual reduction of renal arterial pressure. In control experiments, glomerulotubular balance applied over the whole range of glomerular filtration rate (GFR) examined but was absent after acetazolamide administration (30 mg/kg body wt) at GFR above 50 % of control. Hence, the inhibitory effect of acetazolamide varied with GFR. At control GFR, acetazolamide reduced tubular sodium reabsorption by 32 ±2%, chloride reabsorption by 34 ±3%, and bicarbonate reabsorption by 52±2%; no significant effect was observed at GFR below 50% of control. For each bicarbonate ion, three sodium ions and two chloride ...

Secretin empties bile duct cell cytoplasm of vesicles when it initiates ductular HCO3− secretion in the pig

To determine whether secretin has any effect on bile duct cell ultrastructure, bile duct cells from liver biopsy specimens of pigs were analyzed morphometrically. During secretory rest, bile duct cell cytoplasmic vesicles totaled 96 (84-103) arbitrary units per cell volume (U). Secretin increased bile HCO3- secretion from 9 mumol/min (range 6-15) to 131 mumol/min (range 118-200) and lowered the bile duct cell vesicles to 5 U (range 3-9). Acute elevation of arterial PCO2 to 10.9 kPa (range 10.2-11.1) doubled vesicle number in resting duct cells and augmented the secretory response to secretin. At high arterial PCO2, secretin cleared the duct cell cytoplasm of vesicles and more than doubled the basolateral plasma membrane surface area. Taurocholate-induced canalicular choleresis, in contrast, did not alter duct cell morphology. It is concluded that secretin clears the bile duct cell cytoplasm of vesicles as it initiates ductular HCO3- secretion, possibly through causing exocytotic insertion of vesicle material into the basolateral plasma membrane.

ABCB4 sequence variations in young adults with cholesterol gallstone disease

Background and Aims: Mutations in the gene encoding the ABCB4 [adenosine triphosphate (ATP)‐binding cassette, sub‐family B (MDR/TAP), member 4] transporter lower phosphatidylcholine output into bile and contribute to cholesterol gallstone formation by decreasing the solubility of cholesterol in bile. Mutations in ABCB4 have been identified in patients with low phospholipid‐associated cholelithiasis. The aim of the present study was to determine the types and frequencies of ABCB4 mutations in cholecystectomized patients aged <40 years.

Cardiomyocyte-specific disruption of Serca2 in adult mice causes sarco(endo)plasmic reticulum stress and apoptosis

Reduced sarco(endo)plasmic reticulum (SR) Ca(2+) ATPase (SERCA2) contributes to the impaired cardiomyocyte Ca(2+) homeostasis observed in heart failure. We hypothesized that a reduction in SERCA2 also elicits myocardial ER/SR stress responses, including unfolded protein responses (UPR) and cardiomyocyte apoptosis, which may additionally contribute to the pathophysiology of this condition. Left ventricular myocardium from mice with cardiomyocyte-specific tamoxifen-inducible disruption of Serca2 (SERCA2 KO) was compared with aged-matched controls. In SERCA2 KO hearts, SERCA2 protein levels were markedly reduced to 2% of control values at 7 weeks following tamoxifen treatment. Serca2 disruption caused increased abundance of the ER stress-associated proteins CRT, GRP78, PERK, and eIF2α and increased phosphorylation of PERK and eIF2α, indicating UPR induction. Pro-apoptotic signaling was also activated in SERCA2 KO, as the abundance of CHOP, caspase 12, and Bax was increased. Indeed, TUNEL staining revealed an increased fraction of cardiomyocytes undergoing apoptosis in SERCA2 KO. ER-Tracker staining additionally revealed altered ER structure. These findings indicate that reduction in SERCA2 protein abundance is associated with marked ER/SR stress in cardiomyocytes, which induces UPR, apoptosis, and ER/SR structural alterations. This suggests that reduced SERCA2 abundance or function may contribute to the phenotype of heart failure also through induction of ER/SR stress responses.

Mechanism of hepatic bicarbonate secretion and bile acid independent bile secretion

Abstract. To examine hepatic bicarbonate transport and bile acid independent bile secretion, bile was sampled via a T‐tube inserted into the common bile duct of anaesthetized pigs. Secretin was infused intravenously at a rate of 2.7 C.U./kg body weight h‐1 (large dose) or 0.45 C.U./kg body weight h‐1 (small dose). Hepatic water and electrolyte secretion were studied during systemic acid‐base disturbances while secretin was continuously administered. Systemic acidosis reduced the rate of NaHCO3 secretion which fell in proportion to changes in plasma pH, by 9% and 2% per 0.1 pH unit for the large and small dose of secretin, respectively. Plasma pCO2 and bicarbonate concentration had little influence on NaHCO3 secretion. Consequently, plasma pH appeared to be the main determinant of hepatic NaHCO3 secretion during acid‐base changes. Secretion of 1 mol NaHCO3 was accompanied by an isotonic solution containing water and 0.25 mol NaCl. After secretin infusion, 14C‐erythritol clearance increased in proportion to bile flow. Bicarbonate secretion is determined by a gradient limited H+‐pump at the contraluminal cell. During secretin stimulation bile acid independent bile secretion is osmotically driven by bile NaHCO3 flux.

Aetiology and prognostic implication of severe jaundice in surgical trauma patients

BACKGROUND Pronounced postoperative jaundice occurs not infrequently in trauma patients. The aim of this study was to elucidate the implication of early, pronounced jaundice (serum-bilirubin >100 micromol x l(-1)) for 30-day survival of such patients. METHODS From 1995 through 2001, 53 surgical trauma patients developing pronounced postoperative jaundice were identified. Nine were excluded from the study because of major hepatobiliary injury or pre-existing liver disease. The clinical course and laboratory chemistry profiles of the remaining 44 patients were analysed. RESULTS Thirty-one patients survived and 13 died within 30 days of trauma. Non-survivors had higher age, higher injury severity score (ISS) and lower probability of survival (PS) (P < 0.05) than survivors. ISS averaged 34 in survivors and 45 in non-survivors. Survivors and non-survivors received a mean of 46 (range 10-97) and 55 units of blood (range 11-128), respectively (P = 0.366). Systemic hypotension, local infections and sepsis were common in both groups. Bilirubin levels peaked around the 11th day in survivors (median 189 micromol x l(-1)). In non-survivors, serum bilirubin values rose progressively, reaching maximum levels at time of death (median 231 micromol x l(-1)). These patients died in a setting of sepsis and multiple organ failure. CONCLUSION Large endogenous production of bilirubin because of rapid breakdown of transfused and extravasated blood can cause pronounced jaundice in multitransfused trauma patients. In such patients, serum bilirubin rising >100 micromol x l(-1) does not by itself signal poor outcome. However, progressive pronounced jaundice outlasting the trauma incident by 10-12 days portends fatal outcome for the patient.

Diagnostic approach to the patient with jaundice following trauma

Background and Aims: Jaundice in trauma patients may reflect serious underlying pathology. The aim of this review was to determine the appropriate diagnostic approach to the patient with jaundice following trauma. Methods: A MEDLINE search was performed to retrieve publications which outlined the causes of jaundice in trauma patients. Results: The main causes of jaundice in trauma patients were found to be bilirubin overload caused by breakdown of transfused- and extravasated blood and hepatic dysfunction caused by sepsis, infections, initial shock and systemic hypotension. Bile duct injury or drug induced liver injury are rare. Liver function tests are often uninformative but commonly show a cholestatic pattern. Ultrasound, CT or ERCP are the diagnostic imaging methods most widely used. Abdominal ultrasound and CT may reveal specific organ injuries, bile duct dilatation, intraabdominal fluid collections, hematomas or acalculus cholecystitis. ERCP is often diagnostic and permits a therapeutic intervention when a bile duct injury is present. Conclusions: The primary aim of the diagnostic approach should be to identify all cases of bile duct injury or obstruction. Sepsis and infections should be actively looked for. The number of blood transfusions must be calculated. Ultrasound, CT or ERCP are the diagnostic imaging methods most widely used.

Cholestatic Effect of Large Bilirubin Loads and Cholestasis Protection Conferred by Cholic Acid Co-infusion: a Molecular and Ultrastructural Study

Background: Large intravenous bilirubin loads block biliary phospholipid secretion, produce canalicular membrane lesions and cause canalicular cholestasis. Cholic acid co-infusion forestalls these untoward effects. The aim of this study was first to determine whether bilirubin overload causes cholestasis through reducing the activity or the hepatic expression of the bile salt export pump ( bsep ) or Na-taurocholate cotransporting polypeptide ( ntcp ) and, secondly, whether cholic acid co-infusion forestalls cholestasis by upregulating bsep, ntcp or phosphoglycoprotein 3 ( pgp3 ) expressions or activities. A further aim was to determine whether large bilirubin infusions also produce ultrastructural changes inside hepatocytes. Methods: The effects of intravenous infusion of 2 g bilirubin over 150 min on hepatic expression of bsep, ntcp and pgp3 were studied in bile acid-depleted and cholic acid co-infused pigs, and related to canalicular bile acid transport and bile secretion. Effects on hepatocyte ultrastructural morphology were analysed by electron microscopy. Results: Bilirubin-induced cholestasis reflected marked diminution of bsep and pgp3 transport activities and not reduced hepatic expression of these transporters. Hepatocyte ultrastructural abnormalities were predominantly confined to the hepatocyte canalicular membrane in cholestatic livers. Cholic acid co-infusion with bilirubin conferred complete cholestasis protection through enhancing pgp3 and bsep transporter activities and not through upregulating their expression. Bilirubin infusion did not change ntcp expression. Conclusion: Bilirubin-induced cholestasis is due to markedly impaired activity of the membrane-embedded bsep transporter consequent upon ultrastructural injury to the canalicular membrane. Cholic acid co-infusion with bilirubin enhances bsep and pgp3 activities and confers protection against canalicular membrane injury and bilirubin-induced cholestasis.