Interactions Between Ionized Calcium and Sodium Taurocholate: Bile Salts Are Important Buffers for Prevention of Calcium-Containing Gallstones

Effect and mechanism of endoclip papilloplasty in reducing the incidence of cholelithiasis

BACKGROUND

Endoscopic sphincterotomy (EST) is widely used to treat common bile duct stones (CBDS); however, long-term studies have revealed the increasing incidence of recurrent CBDS after EST. Loss of sphincter of Oddi function after EST was the main cause of recurrent CBDS. Reparation of the sphincter of Oddi is therefore crucial. This study aims to investigate the effectiveness and safety of endoclip papilloplasty (ECPP) for repairing the sphincter of Oddi and elucidate its mechanism.

METHODS

Eight healthy Bama minipigs were randomly divided into the EST group and the ECPP group at a 1:1 ratio, and bile samples were collected before endoscopy and 6 months later. All minipigs underwent transabdominal biliary ultrasonography for the diagnosis of cholelithiasis 6 months after endoscopy. The biliary microbiota composition and alpha and beta diversity were analyzed by 16S rRNA gene sequencing. Differential metabolites were analyzed by bile acid metabolomics to explore the predictive indicators of cholelithiasis.

RESULTS

Three minipigs were diagnosed with cholelithiasis in the EST group, while none in the ECPP group showed cholelithiasis. The biliary Firmicutes/Bacteroidota (F/B) ratio was increased after EST and decreased after ECPP. The Chao1 and observed species index significantly decreased 6 months after EST (P = 0.017 and 0.018, respectively); however, the biliary α-diversity was similar before and 6 months after ECPP. The β-diversity significantly differed in the EST group before and 6 months after EST, as well as in the ECPP group before and 6 months after ECPP (analysis of similarities [ANOSIM]: R = 0.917, P = 0.040; R = 0.740, P = 0.035; respectively). Glycolithocholic acid (GLCA) and taurolithocholic acid (TLCA) accumulated in bile 6 months after EST.

CONCLUSIONS

ECPP has less impact on the biliary microenvironment than EST and prevents duodenobiliary reflux by repairing the sphincter of Oddi. The bile levels of GLCA and TLCA may be used to predict the risk of cholelithiasis.

Structural Changes in Liposomal Vesicles in Association with Sodium Taurodeoxycholate

Liposomes composed of soy lecithin (SL) have been studied widely for drug delivery applications. The stability and elasticity of liposomal vesicles are improved by incorporating additives, including edge activators. In this study, we report the effect of sodium taurodeoxycholate (STDC, a bile salt) upon the microstructural characteristics of SL vesicles. Liposomes, prepared by the thin film hydration method, were characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), electron microscopy, and rheological techniques. We noticed a reduction in the size of vesicles with the incremental addition of STDC. Initial changes in the size of spherical vesicles were ascribed to the edge-activating action of STDC (0.05 to 0.17 µM). At higher concentrations (0.23 to 0.27 µM), these vesicles transformed into cylindrical structures. Morphological transitions at higher STDC concentrations would have occurred due to its hydrophobic interaction with SL molecules in the bilayer. This was ascertained from nuclear magnetic resonance observations. Whereas shape transitions underscored the deformability of vesicles in the presence of STDC, the consistency of bilayer thickness ruled out any dissociative effect. It was interesting to notice that SL-STDC mixed structures could survive high thermal stress, electrolyte addition, and dilution.

ABO-Incompatible Liver Transplantation under the Desensitization Protocol with Rituximab: Effect on Biliary Microbiota and Metabolites

Background: ABO-incompatible liver transplantation (ABOi LT) under the desensitization protocol with rituximab had excellent survival outcomes comparable to those of ABO-compatible liver transplantation (ABOc LT). In this work, we explored the effect of ABOi LT on recipients from the perspective of biliary microbiota and metabonomics. Methods: Liver transplant (LT) recipients treated at our center were enrolled in the study. In total, 6 ABOi LT recipients and 12 ABOc LT recipients were enrolled, and we collected their bile five times (during LT and at 2 days, 1 week, 2 weeks and 1 month after LT). The collected samples were used for 16S ribosomal RNA sequencing and liquid chromatography mass spectrometry analysis. Results: We obtained 90 bile samples. Whether in group ABOi LT or ABOc LT, the most common phyla in all of the samples were Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria. The most common genera were Lactobacillus, Weissella, Klebsiella, Pantoea and Lactococcus. There was no significant difference in the diversity between the two groups at 1 week, 2 weeks and 1 month after LT. However, the biggest disparities between the ABOi LT recipients and ABOc LT recipients were observed 2 days after LT, including increased biodiversity with a higher ACE, Chao1, OBS and Shannon index (p < 0.05), and more Staphylococcus in ABOi LT and binary−Jaccard dissimilarity, which indicated varying β-diversity (p = 0.046). These differences were not observed at 1 week, 2 weeks and 1 month after LT. The principal coordinate analysis (PCoA) revealed that the composition of the bile microbiota did not change significantly within 1 month after LT by longitudinal comparison. In an analysis of the bile components, the metabolites were not significantly different every time. However, four enrichment KEGG pathways were observed among the groups. Conclusion: These findings suggest that ABOi LT under the desensitization protocol with rituximab did not significantly affect the biliary microbiota and metabolites of recipients.

Improved in vitro bioavailability of a newly developed functionalized calcium carbonate salt as a food ingredient and its comparison with available commercial calcium salts

The bioaccessibility and bioavailability of a functionalized Calcium (Ca) salt as food ingredient, based on modified Ca carbonate and hydroxyapatite (FCC), was determined and compared with frequently used Ca sources (Ca citrate tetrahydrate (CCT), tri-Ca phosphate (triCP) and Ca carbonate (CC). Results showed a similar Ca bioaccessibility for CCT (76.44 ± 9.73%), CC (73.7 ± 8.18%) and FCC (74.4 ± 1.87%) and a lower value for tri-CP (46.07 ± 8.68%). FCC showed the highest bioavailability, 5.68 ± 0.26%, compared to CC, CCT and tri-CP (3.93 ± 0.99%, 3.41 ± 0.33%, 1.85 ± 0.34%, respectively). The innovative chemical composition and structure of FCC based on amorphous hydroxyapatite combined with Ca carbonate, a greater porosity, lower agglomerates and particle size, improve the Ca solubility in the intestinal media, explaining the similar bioaccessibility but higher bioavailability of FCC compared to CCT, tri-CP and CC.

Calcium Enhances Bile Salt-Dependent Virulence Activation in Vibrio cholerae

Vibrio cholerae is the causative bacteria of the diarrheal disease cholera, but it also persists in aquatic environments, where it displays an expression profile that is distinct from that during infection. Upon entry into the host, a tightly regulated circuit coordinates the induction of two major virulence factors: cholera toxin and a toxin-coregulated pilus (TCP). It has been shown that a set of bile salts, including taurocholate, serve as host signals to activate V. cholerae virulence through inducing the activity of the transmembrane virulence regulator TcpP. In this study, we investigated the role of calcium, an abundant mental ion in the gut, in the regulation of virulence. We show that whereas Ca²⁺ alone does not affect virulence, Ca²⁺ enhances bile salt-dependent virulence activation for V. cholerae The induction of TCP by murine intestinal contents is counteracted when Ca²⁺ is depleted by the high-affinity calcium chelator EGTA, suggesting that the calcium present in the gut is a relevant signal for V. cholerae virulence induction in vivo We further show that Ca²⁺ enhances virulence by promoting bile salt-induced TcpP-TcpP interaction. Moreover, fluorescence recovery after photobleaching (FRAP) analysis demonstrated that exposure to bile salts and Ca²⁺ together decreases the recovery rate for fluorescently labeled TcpP, but not for another inner membrane protein (TatA). Together, these data support a model in which physiological levels of Ca²⁺ may result in altered bile salt-induced TcpP protein movement and activity, ultimately leading to an increased expression of virulence.

Roles of Sphincter of Oddi Laxity in Bile Duct Microenvironment in Patients with Cholangiolithiasis: From the Perspective of the Microbiome and Metabolome

BACKGROUND

Bile duct microenvironment plays several key roles in cholangiolithiasis occurrence. Sphincter of Oddi laxity (SOL) is associated with cholangiolithiasis, probably due to enhanced reflux of intestinal contents that changes the microenvironment. However, the microenvironment has not been investigated comprehensively.

STUDY DESIGN

Patients with cholangiolithiasis were consecutively recruited and their bile was collected intraoperatively for high-throughput experiments. Pyrosequencing of 16S ribosomal RNA gene was performed to characterize the microbiota in the bile. A liquid chromatography mass spectrometry-based method was used to profile bile composition. Clinical manifestation, microbiome, and bile composition were compared between patients with and without SOL.

RESULTS

Eighteen patients with SOL and 27 patients without SOL were finally included. Patients with SOL showed more severe inflammation. Bacteria in the bile duct were overwhelmingly aerobes and facultative anaerobes. Proteobacteria and Firmicutes were the most widespread phylotypes, especially Enterobacteriaceae. Compared with those without SOL, patients with SOL possessed more varied microbiota. In the SOL group, pathobionts, such as Bilophila and Shewanella algae had richer communities, and harmless bacteria were reduced. Metabolomics analysis showed the differences in bile composition between groups were mainly distributed in lipids and bile acids. Particularly, the increased abundance of Bilophila involved in taurine metabolism was associated with reduced contents of taurine derivatives in the bile of patients with SOL.

CONCLUSIONS

A bile duct microenvironment with more severe bacterial infection and stronger lithogenicity was found in patients with SOL. The findings suggest a possible mechanism of cholangiolithiasis and provide the basis for future strategies for prevention of cholangiolithiasis recurrence.

Influence of La3+ ions on the egg-yolk phosphatidylcholine and sodium taurocholate self-assemblies in aqueous suspension

In this study, the influence of La3+ on the mixed egg-yolk phosphatidylcholine (EYPC)-sodium taurocholate (TC) aggregates was investigated by using turbidity, quasi-elastic light-scattering (QELS) technique, Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). La3+ ions exert different effects on different EYPC-TC aggregates. The EYPC-TC mixed spheroidal micelles are stable in the presence of La3+ ions. The EYPC-TC vesicles are aggregated by the interaction of La3+ with the EYPC phosphate group. Particularly, La3+ causes structural transition of the EYPC-TC mixed disk micelles by changing the colloidal properties of TC. This process includes two steps, destruction of mixed disk micelles and formation of mixed spheroidal micelle. Several intermediate structures such as multi-lamellar vesicles and cylindrical micelles were observed during the transition. The experimental data and analysis in the current study suggest that metal ion is one of the important factors to control the structure of the EYPC-TC self-assemblies. And the possible influence of metal ions on the properties of bile biocolloid has been discussed.

The interaction of Cu2 + ions and NaDC micelles

By mixing an aqueous solution of CuCl2 with an NaDC aqueous solution of various concentration and initial molar ratio, seven coordinated samples with distinct appearances and characters were obtained. Their structures and components were investigated by FT-IR spectroscopy, EXAFS (the extended X-ray absorption fine structure), thermal analysis, X-ray diffraction, laser light scattering, TEM (transmission electron micrograph), element analysis and ICP (inductively coupled plasma) analysis. The following conclusions were given: (1) The complexes of Cu2+-NaDC with distinct appearances and properties were synthesized. (2) After Cu(DC)2 dissolved in NaDC aqueous solution, larger micelles (30-90 nm diameter) formed in the supernate, it is a mixed micelle with Cu(DC)2 and NaDC. So these micelles are a new kind of micelle containing two kinds of metal ions. This is a new result using metal ions as bridges to form micelle. (3) According to the different concentration of Cu2+ to NaDC, the complexes formed as gel or poly-crystals. Both the composition of gel complexes and the coordination structure of carboxyl groups with metal ions varied with the initial molar ratio of Cu2+ to Na+. The gel complexes exhibits the non-stoichiometric character. (4) These results are in agreement with physiological condition. All the different states such as gel, precipitate, micelles of various structures are present in bile of gallbladder. We can suggest an ideal model of the interaction between Cu2+ and bile salts in vivo.

Cesium cholate: determination of X-ray crystal structure indicates participation of the ring hydroxyl groups in metal binding

The crystal structure of cesium cholate, C(24)H(36)(OH)(3) COOCs has been determined with three-dimensional X-ray diffractometer data. It crystallized in the monoclinic space group P2(1) with unit-cell dimensions a = 11.543(5) A, b = 8.614(3) A, and c = 12.662(5) A, beta(deg) = 107.95(2), V = 1197.7 A(3) and Z = 2. The atomic parameters were refined to a final r = 0.0269 and R(omega) = 0.0280 for 2342 observed reflections. Each Cs(+) is coordinated to 7 oxygen atoms from 5 different cholate anions with Cs-O distances ranging from 2.957(4) A to 3.678(5) A. In this crystal, 5 cholates are coordinated with 1 Cs(+), and 5 Cs(+) are coordinated with 1 cholate anion. Carboxyl and all the 3 ring hydroxyl groups of cholate anion participate in binding to Cs(+) simultaneously, and there is no water molecule coordinated with the Cs(+). The pattern of successive rows arranged with polar (p) and non-polar (n) faces in apposition leads to the formation of a sandwich sheet structure with polar and non-polar channels. The Cs ions lie within the polar interior of the sandwich. The H-bond network is reorganized in forming cesium cholate from cholic acid. All the oxygen atoms in cholate anion are involved in H-bonding reciprocally or with water molecules to form an extensive 3-dimensional network of H-bonds. Compared with cholic acid and other similar type of steroids, the coordination structure and H-bonding of Cs cholate crystal are distinct.

Biliary electrolytes and enzymes in patients with and without gallstones

pH, osmolarity, various electrolytes, nine enzymes, and bile acid were determined in hepatic and gallbladder biles from 108 and 100 patients, respectively, relating to various types of gallstones. The pH, osmolarity, and electrolytes were essentially identical in all groups of patients except for slightly higher Ca and Mg in the hepatic bile in patients with muddy pigment stones. The gallbladder bile contained much higher inorganic cations yet remained isosmotic as a result of their sequestration into bile acid micelles. Excluding extremely high values, the activities of nine enzymes in the bile showed only minor differences among four groups of patients except for a high beta-glucuronidase activity in the hepatic bile in patients with muddy pigment stones. The biliary baseline activities of various enzymes and the relation to their serum levels were determined by their sources and subcellular localization in the hepatocytes. We concluded that biliary electrolytes and enzymes were basically similar in patients with and without gallstones except for higher levels of Ca, Mg, and beta-glucuronidase in hepatic bile in patients with muddy pigment stones.

Intestinal transport of calcium in rat biliary cirrhosis

The characteristics of intestinal calcium transport in chronic cholestasis remain largely unknown. Using an experimental model of biliary cirrhosis in the rat, we aimed to investigate changes in calcium transport at the jejunal and ileal levels. Two methods were used: 1) uptake of 45Ca in brush border membrane vesicles and 2) measurements of transepithelial fluxes of calcium in Ussing chambers. Thirty days postsurgery, cholestatic rats presented biliary cirrhosis, with normal growth, normal daily energy, and calcium intakes, but had depressed circulating levels of 25-(OH)-vitamin D2 and 1,25-(OH)-vitamin D3. Compared with sham-operated controls, 45Ca uptake ([Ca2+] = 0.03 mmol) measured in vesicles from cholestatic rats was decreased by 3-fold in the duodenojejunum, in concordance with a lower content in brush border membrane calmodulin. Other changes in brush border membrane composition included decreases in structural proteins, microvillous enzymes, and in triglyceride content. Transepithelial fluxes of calcium measured in the ileum ([Ca2+] = 1.2 mmol) revealed in controls a net basal secretion flux (Jnet = -30.4 +/- 8.1 mmol.h-1.cm-2) that was reduced by 3-fold (p < 0.05) in vitamin D-deficient rats (Jnet = -10.4 +/- 4.8 mmol.h-1.cm-2). In response to 25-(OH)-vitamin D2 treatment, calcium uptake rates increased by 40% in the jejunum, whereas in the ileum, the secretion flux returned to basal control levels. Oral administration of taurocholate or tauroursodeoxycholate (50 mmol) depressed almost completely calcium uptake capacity in the duodenojejunum. By complexing free calcium, tauroconjugated bile acids inhibited in vitro calcium uptake proportionally to their concentration in the medium (0-40 mmol). Our data indicate that, in rat biliary cirrhosis, transport capacity of calcium in the duodenojejunum is markedly reduced in association with vitamin D deficiency and alterations in brush border membrane composition.

Influence of phospholipid on bile salt binding to calcium hydroxyapatite and on the poisoning of nascent hydroxyapatite crystals

Glycine-conjugated, dihydroxy bile salts inhibit calcium hydroxyapatite (HAP) formation by binding to and poisoning nascent crystal embryos. Their taurine-conjugated counterparts bind less well to hydroxyapatite and do not inhibit its formation; but more hydrophobic, synthetic analogs of the taurine conjugated bile salts are inhibitors of hydroxyapatite formation. Because hydrophobicity is an important determinant of the ability of bile salts to inhibit hydroxyapatite crystal growth, experiments were performed to study the effect of the physiologically important mixed micelles of bile salt and phospholipid. Taurodeoxycholate/phosphatidylcholine (10:1) mixed micelles bound to HAP at lower total lipid concentrations than did pure taurodeoxycholate. At low total lipid concentrations, phosphatidylcholine (PC) binding appeared to predominate, suggesting that PC had a higher affinity than did taurodeoxycholate (TDC) for the HAP surface. Although glycodeoxycholate (3 mM) significantly (> 95%) inhibited hydroxyapatite precipitation, higher concentrations of taurodeoxycholate, either alone or mixed with phosphatidylcholine, did not affect hydroxyapatite formation. These results suggest that biliary phospholipids do not modulate the ability of bile salts to inhibit hydroxyapatite crystal growth.

Inflammatory properties of bile from dogs with pigment gallstones

BACKGROUND

Gallbladder inflammation and mucus hypersecretion are prominent features of cholesterol and pigment gallstones in humans and animals. The factors leading to inflammation and mucus hypersecretion are poorly understood. These studies examine the inflammatory potential of bile from dogs with pigment gallstones.

METHODS

Dogs fed a methionine-deficient diet that produces pigment gallstones by 6 weeks were compared to normal dogs. Mucus layer thickness, myeloperoxidase activity, and interleukin-1-like activities were measured in canine gallbladder. The inflammatory potential of canine bile was determined by measuring mucus layer thickness, sodium absorption, myeloperoxidase activity and interleukin-1-like activity in guinea pig gallbladders exposed to normal and lithogenic canine bile for 4 hours.

RESULTS

Mean mucus layer thickness, myeloperoxidase, and interleukin-1 activity were significantly greater in canine gallbladders containing pigment gallstones. Bile from dogs with pigment gallstones markedly increased mucus layer thickness, myeloperoxidase activity, and interleukin-1 activity and decreased sodium absorption in normal guinea pig gallbladder. These effects were not eliminated by centrifuging bile to remove crystals and gallstones.

CONCLUSIONS

Canine bile from dogs with pigment gallstones contains soluble factors capable of causing inflammation in the gallbladder wall.

Hypercalcemia decreases bile flow and increases biliary calcium in the prairie dog

BACKGROUND

Biliary calcium is known to play an important role in the pathogenesis of gallstones. Calcium salts are present in all pigment gallstones and are also present in the core of most, if not all, cholesterol gallstones.

METHODS

The effects of acute hypercalcemia on bile flow and biliary calcium secretion were examined in 22 prairie dogs during intravenous taurocholate infusion (0, 1.0, 2.25, and 4.5 mumol/kg/min).

RESULTS

Bile flow was linearly correlated with bile acid output in both control (y = 7.62x + 13.5, r = 0.98) and hypercalcemic (y = 7.00x + 10.4, r = 0.96) animals. At lower bile acid outputs (< 3.0 mumol/kg/min), biliary ionized calcium output per increment bile acid output was significantly increased in hypercalcemic animals (0.016 versus 0.011 mumol Ca++ mumol taurocholate, p < 0.001). Bile ionized calcium concentrations approximated Gibbs-Donnan predicted values only at low bile flow rate.

CONCLUSIONS

Hypercalcemia decreases bile flow and increases biliary ionized calcium concentration in the prairie dog. These effects favor the precipitation of calcium salts in bile.

Interaction between Cu2+ ions and cholic acid derivatives followed by polarography

Interaction of bile salts with Cu2+ ions in unbuffered systems containing 0.15 M NaNO3 was followed by measuring polarographic limiting currents and half-wave potentials. Whereas taurocholate forms neither soluble complexes nor compounds of limited solubility, cholate, glycocholate, and dehydrocholate from both soluble complexes and slightly soluble salts of copper(II) with small aggregates of bile salts. The stability of soluble complexes is comparable for cholates, dehydrocholates, acetates, and acetylglycinates, but smaller for glycocholates. The solubility of the copper(II) salts with small aggregates decreases in the sequence: glycocholate > cholate >> dehydrocholate. It is proposed that these salts are formed by interaction of a copper(II) ion with two carboxylic groups located on the small aggregate in a sufficiently small distance. In the presence of excess cholate the precipitated copper(II) salts are dissolved. It is assumed that at high bile salt concentrations, where precipitates are not observed, larger aggregates are formed that have free carboxylate groups, which increase their solubility in aqueous solutions. For glycocholate, within the accessible concentration range and within the time-frame used (24 h for the establishment of the equilibrium), the formation of such larger aggregates was not observed, even when its "cmc" is comparable with that of cholate. The absence of formation of larger aggregates for dehydrocholate parallels its tendency not to form "micelles".

Calcium affinity for biliary lipid aggregates in model biles: complementary importance of bile salts and lecithin

BACKGROUND/AIMS

Despite putative roles of calcium in biliary physiology and gallstone formation, quantitative aspects of calcium binding to bile salt (BS) monomers, simple micelles, mixed micelles, and vesicles, which constitute the lipid aggregates in bile, remain unexplored.

METHODS

Calcium activity was measured using the calcium electrode in pathophysiologically relevant model biles composed of either individual BS species or a physiological mixture of glycine and taurine conjugates, as functions of lecithin and cholesterol contents and total lipid concentration.

RESULTS

Calcium binding increased with increasing BS concentrations and lecithin contents and varied with species (dihydroxy > trihydroxy BS) and with conjugation (unconjugated > glycine conjugates > taurine conjugates). Although lecithin/cholesterol vesicles did not bind detectable calcium, when taurocholate was incorporated into membrane bilayers, calcium binding was substantially greater than with equimolar BS alone. Added cholesterol did not alter calcium binding, despite cholesterol saturation of biliary lipid aggregates and induction of liquid crystalline and solid crystalline-phase transitions.

CONCLUSIONS

In model biles, most calcium is bound to mixed micelles, with minor contributions by BS monomers, simple micelles, and vesicles. It is proposed that BS-induced binding of calcium to vesicles and mixed micelles may be important in nucleation of cholesterol and bilirubinates from native bile.

Premicellar taurocholate enhances calcium uptake from all regions of rat small intestine

BACKGROUND/AIMS

The specific components of bile, which is necessary for normal calcium absorption, are unknown. We have previously shown that Ca2+ is bound with high affinity by premicellar taurocholate. The current studies examined the effects of taurocholate on intestinal calcium transport.

METHODS

Intestinal Ca2+ uptakes were measured from proximal, mid, and distal small intestinal segments perfused with solutions containing 45CaCl2 (0.1-1 mmol/L), taurocholate (0-10 mmol/L), trihydroxymethylaminomethane buffer (pH 7), phenolsulfonpthalein (nonabsorbable marker), and NaCl (total ionic strength, 0.16 mol/L) for four randomized perfusion periods. In other studies, the proximal small intestine was divided into two equal segments and perfused with either 45CaCl2 or 45CaCl2 plus taurocholate (2.5-5 mmol/L). Calcium absorption was measured from the difference in uptake and calcium concentration retained in mucosa. Finally, effects of taurocholate on Ca2+ uptake across isolated brush border membrane vesicles were measured.

RESULTS

Premicellar taurocholate produced an approximately 1.7-2-fold enhancement (P < 0.01) in Ca2+ uptake in all regions, with lesser contributions from micellar taurocholate. These effects resulted in a net increase in calcium absorption. Premicellar taurocholate also significantly increased calcium uptake across brush border vesicles.

CONCLUSIONS

Premicellar taurocholate significantly enhances calcium uptake into, and absorption across, enterocytes. The mechanisms remain to be experimentally verified.

Inhibition of calcium hydroxyapatite formation by polyamines

The lithogenic potential of bile depends not only on supersaturation of solutes but also on the presence of pro- and anti-nucleating factors. For example, glycine-conjugated dihydroxy bile salt dimers are potent inhibitors of calcium hydroxyapatite precipitation that function by "poisoning" the nascent crystal. Although most inhibitors of apatite formation are anions, theoretically polycations should also be effective, and because significant concentrations of polyamines are present in bile, we have investigated the ability of these molecules to inhibit apatite formation. In vitro, each polyamine (2-10 mmol/l) was able to inhibit apatite formation, and the inhibiting power was correlated with ionic charge. Thus putrescine (2+) was the weakest inhibitor and spermine (4+) was the strongest. Mixtures of polyamines were less effective than were the individual polyamines, except at higher concentrations. Although polyamines were effective over short periods of time (270 min), over longer times (3 days) spermine was unable to prevent apatite formation. Using infrared spectroscopy, we found no evidence for interaction between phosphate ions and spermine in solution. Taken together, these results suggest that polyamines are modest inhibitors of apatite formation that likely function by retarding the dissolution of the intermediate amorphous calcium phosphate phase.

Fecal bile acid excretion and composition in response to changes in dietary wheat bran, fat and calcium in the rat

The effect and possible interactive influence of different dietary amounts of wheat bran, fat and calcium on the fecal excretion, concentration and composition of bile acids was studied in Fischer-344 rats. The fecal bile acids were analyzed using gas-liquid chromatography. Dietary wheat bran increased both total bile acid excretion and fecal weight without changes in fecal bile acid concentration. The proportion of fecal hyodeoxycholic acid decreased with increasing dietary fiber, whereas that of lithocholic and deoxycholic acids increased significantly with fiber intake. The percent content of fecal chenodeoxycholic acid did not change. Increasing dietary fat led to an increase in bile acid excretion without changes in either fecal weight or bile acid concentration. In contrast, the level of dietary calcium did not affect the total excretion of bile acids. However, since calcium increased the fecal weight, it consequently diluted bile acids and decreased their fecal concentration. Dietary fat and calcium had no influence on fecal bile acid composition. There were no interactive effects of wheat bran, fat and calcium on fecal bile acids. The finding in this study that dietary fiber, fat and calcium induce significant changes in fecal bile acids may be of relevance to the potential of bile acids to promote carcinogenesis.

High-affinity binding is essential for enhancement of intestinal Fe2+ and Ca2+ uptake by bile salts

Both calcium and iron are bound with high affinity by premicellar bile salts having cholanic ring 7-OH and/or 12-OH groups, forming soluble cation-bile salt complexes. The authors of the current study recently showed that premicellar taurocholate markedly enhances intestinal iron and calcium uptake. However, the relationship of high-affinity binding to the observed uptake enhancement was unknown. In the current study, this relationship was examined by studying taurodehydrocholate (TDHC) binding and intestinal uptake of both cations. Ca2+ binding was measured by noting depression of [Ca2+] activity in solutions containing constant total Ca concentrations (1 mmol/L) and varying [TDHC] (0.5-50 mmol/L). Fe2+ binding was assessed by equilibrium dialysis studies of 59FeSO4 (0.179-1.79 mmol/L) and TDHC (0.5-50 mmol/L). Effects of TDHC on intestinal Fe2+ and Ca2+ uptake were measured in isolated perfused intestinal segments in vivo in seven and eight Sprague-Dawley rats, respectively. TDHC, lacking ring OH groups, did not bind either cation with high affinity and had no effect on their intestinal uptake. These results suggest that high-affinity binding is essential for bile salt-induced enhancement of intestinal Fe2+ and Ca2+ uptake.

Evidence of hydrogen ion secretion from the human gall bladder in vitro

Gall bladder bile is more acid that hepatic bile and this has been attributed to bicarbonate absorption by the gall bladder epithelium. The aim of this study was to investigate in vitro the acid base changes that occur across the human gall bladder mucosa. Fresh gall bladder tissue was obtained at cholecystectomy and placed in an Ussing Chamber and perfused with Ringer-Krebs glucose bicarbonate solution. The viability of the gall bladder was assessed by measuring the potential differences across the epithelium and by the morphology of the epithelial cells at the end of the experiments. Aliquots from the solutions were taken at two, 45 and 70 minutes and pCO2, hydrogen ion and bicarbonate concentrations were measured. In the mucosal side of the chamber a consistent and significant decrease was observed from two minutes to 70 minutes in bicarbonate concentration while pCO2 and hydrogen ion concentrations significantly increased. The degree of inflammation correlated well with the ability for acidification, the more inflamed the tissue the less its ability to acidify. When the gall bladder was exposed to amiloride or sodium free solution acidification was abolished in the mucosal side. When tissue metabolism was irreversibly inhibited by exposure to formaldehyde, hydrogen ion concentration and pCO2 were significantly decreased in the mucosal side of the chamber compared with the viable gall bladder. The human gall bladder is capable of secreting acid and this may be an important mechanism for preventing calcium precipitation and gall stone formation.

Premicellar taurocholate enhances ferrous iron uptake from all regions of rat small intestine

Inorganic iron is virtually insoluble at the pH of small intestinal contents. This severe solubility limitation has been partly overcome by intraluminal substances that bind and solubilize iron, thus increasing availability for absorption. While several dietary ligands capable of solubilizing Fe2+ in intestinal lumen have been described, an endogenous binding ligand has not been previously described. It has recently been shown that certain trihydroxy bile acids (taurocholate and glycocholate) show high-affinity premicellar and low-affinity micellar Fe(2+)-binding properties, resulting in the formation of soluble Fe(2+)-bile salt complexes. It was hypothesized that this binding would increase the intraluminal pool of soluble iron, increase delivery of soluble iron to mucosal carriers, and thus enhance intestinal Fe2+ uptake. As a first step toward testing this hypothesis, the effect of taurocholate on Fe2+ uptake from all regions of in vivo rat small intestine is reported. It is shown that taurocholate, at premicellar concentrations, produces a marked, stepwise increase in Fe2+ uptake from all regions of small bowel, with little further increase above the critical micellar concentration. Enhancement of intestinal Fe2+ uptake is a newly described effect, and potential physiological function, of premicellar bile salts.

Biliary secretion of trace elements and minerals in the rat. Effects of bile flow variation and diurnal rhythms

Effects of bile flow variations on bile secretion of trace elements were systematically evaluated by Proton-Induced X-ray Emission (PIXE) in the unanesthetized rat: (i) longitudinally for a 9 day-period of bile drainage; (ii) continuously for a period of 24 h, to include circadian rhythm and (iii) during exogenous bile salt administration. Potassium and Ca were determined for comparative purposes. In rat bile, six trace elements could always be detected by PIXE (Fe, Zn, Cu, Mo, Mn, Br); occasionally some V, Cr, Sr and Pb was found. Se could not be detected in bile. Bile-plasma concentration ratios of the elements could arbitrarily be divided into three groups: Fe, Zn and Se less than 1; Ca, K, Cu, Mo and Br approx. 1 and Mn much greater than 1. After interruption of the enterohepatic circulation, bile flow and bile salt concentration dropped sharply within 4 h to 36% and 4% of their initial values, respectively. Output rates of K, Ca, Mo, Br, Zn and Fe closely followed the decrease in bile flow; bile secretion of Mn and Cu, on the other hand, was minimally affected. A circadian rhythm was observed for all detectable elements; during the night period, secretion rates of Zn, Fe, Ca and K increased maximally by 60-80% and that of Mn, Mo, Br and Cu by 30-50%. Bile salt output and bile flow increased maximally by 70% and 50%, respectively, in the same time interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Total biliary protein, mucus glycoproteins, cyclic-AMP, and apolipoproteins in the gallbladder bile of patients with cholesterol stones and stone-free controls

The concentrations of total protein, mucus glycoprotein, cyclic-AMP, and apolipoproteins A-I, A-II, and B were determined in the gallbladder bile of patients with cholesterol gallbladder stones and in stone-free controls. The total protein content was significantly increased in gallstone patients (2.03 +/- 0.6 versus 1.31 +/- 0.67 mg/ml; p less than 0.05), as was the mucus glycoprotein concentration (380 +/- 88.5 versus 128 +/- 57.2 micrograms/ml; p less than 0.05). The cyclic-AMP concentration in the gallbladder fluid was increased up to 91 +/- 20 pmol/100 microliters in the gallstone subjects, as compared with 46 +/- 26 pmol/100 microliters (p less than 0.01) in stone-free controls. Cyclic-AMP concentrations correlated positively with the glycoprotein content of the bile in cholesterol gallstone patients (r = 0.66; p less than 0.05). The apolipoprotein concentrations were determined by the radial immundiffusion technique. The corresponding values for patients with stones and controls were 7.5 +/- 0.8 versus 3.0 +/- 0.8 for Apo A-I (p less than 0.025), 10.4 +/- 0.6 versus 6.3 +/- 1.3 for Apo A-II (p less than 0.02), and 1.9 +/- 0.5 versus 1.6 +/- 0.2 mg/dl for Apo B (NS), respectively. Biliary proteins probably play an important role in the nucleation process during the pathogenesis of cholesterol gallbladder stones.

Calcium binding to bile salts

Calcium binding to bile salt monomers and micelles is an important issue with respect to the possible (but rare) precipitation of calcium bile salts in the gallbladder. In the present work the binding of Ca2+ to six bile salts was measured in solutions containing 2 to 100 mM bile salts by means of a calcium-sensitive dye, murexide, which determines the ionic calcium concentration. In solutions containing bile salt at concentration higher than 20 mM most, if not all, of the bound Ca2+ is associated with micellar surfaces. The results were analyzed by employing a model which combines specific binding with electrostatic equations and accounts for the system being a closed one. The analysis of Ca2+ binding data considered explicitly the presence of Na+ ions and yielded intrinsic binding coefficients for Ca2+ and Na+ which were utilized to explain and predict binding results for various concentrations of Ca2+, Na+ and bile salts. The calculations indicate that in saline solutions most of the surface sites were bound by Na+, whereas less than 10% were bound by Ca2+ even in the presence of 8 mM Ca2+. The binding of Ca2+ to bile salt micelles increases with pH. An increase in temperature results in reduced binding affinity of Ca2+ to the bile salt micelles.

Pathogenesis of gallstones

The many developments in nonoperative methods for the treatment of gallstone disease underscore the importance of understanding the pathogenesis of these stones. Elucidation of the factors responsible for nucleation of crystals and the mechanism by which it occurs would appear to be the challenge if we are to define the cascade of events that results in gallstone formation.

Pathogenesis of ceftriaxone-associated biliary sludge. In vitro studies of calcium-ceftriaxone binding and solubility

Ceftriaxone, a semisynthetic third-generation cephalosporin, has recently been associated with biliary sludge formation. Analysis of the biliary concretions induced by this agent shows a calcium salt of ceftriaxone. The present in vitro studies were undertaken to provide insight into the pathogenesis of ceftriaxone-associated biliary sludge formation by evaluating possible interactions that may exist between calcium, bile salts, and ceftriaxone. Ceftriaxone possessed high calcium-binding affinity. The formation constant for the calcium ceftriaxone salt at 37 degrees C was about 157.3 L/mol; stoichiometry of the salt was 1:1, i.e., calcium ceftriaxone. The calcium-binding property of ceftriaxone was observed to be additive to that of taurocholate in mixed taurocholate-ceftriaxone solutions. Although the solubility product constant for calcium ceftriaxone was only 1.62 x 10(-6) mol/L2, marked metastability was observed; neither visible nor microscopic precipitates developed until the [Ca2+] x [ceftriaxone] ion product exceeded the solubility product constant by a factor of 10.4. Metastability of the calcium ceftriaxone salt was also observed in human gallbladder bile in vitro. Estimates of human biliary calcium ceftriaxone solubility in vivo were than calculated from previously-reported values for biliary [Ca2+], [ceftriaxone], and from the solubility product constant as defined in this study. Calculated saturation indices for calcium-ceftriaxone in human bile generally increased (corresponding to a decrease in solubility) with increasing ceftriaxone dose. At doses less than or equal to 1 g, saturation index was well within the metastable range of this calcium-salt. However, at doses greater than or equal to 2 g, the saturation index surpassed the metastable limit. Under these conditions, precipitation of ceftriaxone could occur. It was concluded that the development of ceftriaxone-induced biliary sludge is a solubility problem that occurs in patients receiving high-dose treatment (greater than or equal to 2 g). This study proposes that the risk of developing ceftriaxone-associated biliary "pseudolithiasis" increases with increasing ceftriaxone dose and in patients with impaired gallbladder emptying.

Measurement of calcium content of gallstones by computed tomography and the relationship between gallbladder function and calcification of gallstones

To evaluate the relationship between gallbladder function and calcification of gallstones, we studied gallbladder contractility by oral cholecystography, the computed tomography (CT) number of stones for 30 gallstone patients, calcium content of 13 stones operatively extirpated, and the degree of inflammatory change in 13 surgical gallbladder specimens. There was significant correlation between the calcium content and CT numbers of stones, and 1% of the calcium content of gallstone was approximately equal to 40 Hounsfield Units (HU) of the CT number. The calcium content of stones in patients with normal gallbladder contractility was extrapolated to be below 1.5%, while that with poor contractility ranged from 0% to 21%. Additionally there is a possibility that calcium content increases, related to the inflammatory change of gallbladder. Hence our results suggested that measurement of the CT number of stones is useful to evaluate the calcium content of gallstones, and that the gallbladder contractility could be one of the factors to influence calcification of stones.

A study on the influence of bile acid chemical structure on dissolution of insoluble calcium salts: an in vitro study of the use of bile acid-phosphatidylcholine-cholesterol model bile solution

The influence of bile acid chemical structure on dissolution of insoluble calcium salts and the reducing effect of ionized calcium was studied. Various bile acids were used to compound model bile acid-phosphatidylcholine-cholesterol model bile solutions. After CaCO3 was added to these solutions, both total calcium solubility and ionized calcium concentration in the solutions were measured. Dihydroxy bile acid is more effective than trihydroxy bile acid and 7 alpha-hydroxy bile acid is more effective than 7 beta-hydroxy bile acid, with regard to calcium solubility and the reducing effect of ionized calcium in model bile solution. Glutamic or asparaginic acid conjugates are more effective than glycine or taurine conjugates. Therefore, calcium solubility and the reducing effect of ionized calcium in model bile solutions are dependent on the number and orientation of hydroxy groups on the steroid nucleus as well as electrical charge of conjugating amino acid of bile acid. Chenodeoxycholic acid conjugated with glutamic or asparginic acid possesses high calcium solubility and large binding capacity with ionized calcium.

The role of calcium precipitation in the sulfoglycolithocholate-induced cholestasis of the bile fistula hamster

Sulfate glycolithocholic acid (SGLC) has been shown to be highly cholestatic in the rat. This study was performed in order to gain understanding of the mechanisms of SGLC-induced cholestasis and the aim of the investigation was to explore the hypothesis that SGLC could cause a precipitation of calcium in bile. We studied the effects of intravenously administrated SGLC on bile flow, biliary lipids secretion and calcium excretion in the female bile fistula hamster. We also performed in-vitro studies with a Ca2(+)-selective electrode in order to measure the calcium binding capacity of SGLC. The results showed that after 1 h of infusion of 8 mumol/100 g body weight [14C]SGLC bile flow dropped to zero. During the infusion period a fine white sludge was visible in the test tube used for bile collection. TLC and HPLC analysis of both the supernatant and the precipitate showed that unchanged SGLC was excreted into bile. Up to 20% of biliary SGLC and more than 50% of the total Ca2+ present in bile was precipitated. The SGLC/Ca2+ molar ratio in the precipitate was 1.12 +/- 0.3 (mean +/- S.D. of four experiments). Light and electron microscopy of the liver did not show any specific abnormalities. The Ca2+ binding activity of SGLC in vitro, was highest among the bile acids tested at a concentration of 0.1 mM, when almost 100% of bile acids are in the monomeric (non-micellar) form. This suggests that among the bile acids, SGLC exerts the strongest binding activity on free calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterizing mechanisms of hepatic bile acid transport utilizing isolated membrane vesicles

Utilizing the above-outlined approaches, mechanisms of hepatic bile acid transport have been characterized in membrane vesicles of rat liver, particularly for the conjugated trihydroxy bile acid, taurocholic acid. Uptake across the sinusoidal membrane is carrier mediated and coupled to the transmembrane sodium gradient. This carrier has an apparent Km between 30 to 50 microM and a Vmax between 4 to 6 nmol mg-1 protein min-1. Furthermore, Na+ gradient-dependent sinusoidal uptake of taurocholate can be stimulated by low concentrations of albumin. There is controversy as to whether the process is electrogenic. Although photoaffinity labeling studies indicate that an additional carrier for Na(+)-dependent bile acid uptake is also present at the sinusoidal membrane, this carrier has so far not been characterized in membrane vesicles. The proposition that pH gradient-driven furosemide-sensitive cholic acid uptake into sinusoidal membrane vesicles may represent carrier-mediated hydroxyl/cholate exchange must be revised on the basis of the recent findings that (1) true initial uptake rates are not saturable; (2) pH gradient-driven cholate uptake is also found in liposomes; and (3) furosemide also inhibits pH gradient-driven cholate uptake in liposomes. The mechanisms of transcellular transport of bile acids have been studied less extensively, but Na(+)-independent carrier-mediated taurocholic acid transport has been demonstrated in purified subcellular fractions such as rat liver microsomes and Golgi membranes. Finally, transport studies in canalicular rat liver plasma membrane vesicles indicate that canalicular excretion of bile acids is also a carrier-mediated process that may be driven, at least in part, by the physiologic electrical potential gradient, and that preferentially transports trihydroxy and conjugated dihydroxy bile acids.

High-performance liquid chromatography of bilirubin conjugates in bile: effect of beta-glucuronidase on the bile pigments

A simple, specific, and technically easy high-performance liquid chromatography (HPLC) method for the separation and quantification of unconjugated bilirubin, bilirubin monoglucoside-monoglucuronide, bilirubin diglucuronide, and bilirubin monoglucuronide has been developed. The method was used to determine the bilirubin compounds of bile obtained endoscopically from the common bile duct in 43 patients with gallstone disease and in 6 subjects without gallstones or liver disease. The bile samples were also assessed for the presence of beta-glucuronidase-producing bacteria. The amount of unconjugated bilirubin was significantly higher (p less than 0.01) in bile containing bacteria producing beta-glucuronidase than in bile without such bacterial strains. In six 'normal' bile samples the following quantities of bilirubin conjugates and unconjugated bilirubin were found (median and range): bilirubin monoglucoside-monoglucuronide (mixed conjugate), 61 (27-80) mumol/l; bilirubin diglucuronide, 632 (512-861) mumol/l; bilirubin monoglucuronide, 113 (70-175) mumol/l; and unconjugated bilirubin, 3 (1-7) mumol/l. These results are in good agreement with those obtained with other HPLC methods. The concentrations of unconjugated bilirubin were lower than those found when using conventional diazo methods and thin-layer chromatography. HPLC proved to be a useful tool in gallstone pathogenesis studies. Our results support bacterial glucuronidase as a possible pathogenic factor in pigment gallstone disease.

The effects of intraduodenal bile acid administration on biliary secretion of ionized calcium and carbonate in man

The importance of calcium in gallstone formation is increasingly recognized. Calcium carbonate is an important constituent of gallbladder stones and may be present in the nidus of cholesterol stones. Secondary deposition of calcium carbonate on the surface of cholesterol gallstones is an important reason for failure of oral bile acid dissolution therapy. We sought to determine the effects of bile acids on the crystallization conditions of calcium carbonate in bile. We studied 18 patients with choledocholithiasis with a percutaneous or endoscopically placed catheter high in the biliary tree. Samples of bile in the basal state and following replacement of the bile acid pool with cholic acid, chenodeoxycholic acid and ursodeoxycholic acid were analyzed for total calcium, ionized calcium, bicarbonate and carbonate, and the saturation index for calcium carbonate was calculated. Hepatic bile in the basal state was supersaturated with calcium carbonate. Total calcium concentrations rose linearly with rising bile acid concentrations but ionized calcium was maintained in a relatively narrow range. These data are consistent with an important role for bile acids in binding calcium. Extrapolation of the linear regressions between bile acid concentration and calcium concentrations suggested that in the absence of bile acids, biliary calcium concentrations are in passive equilibrium with plasma. Chenodeoxycholic acid and ursodeoxycholic acid caused a bicarbonate-rich choleresis and significantly augmented the saturation index for calcium carbonate, whereas cholic acid caused no change. In contrast with animal models, the apparent choleretic activity of cholic acid, chenodeoxycholic acid and ursodeoxycholic acid was similar, and no hyper-choleresis was observed with ursodeoxycholic acid. Chenodeoxycholic acid and ursodeoxycholic acid therefore increase the thermodynamic possibility for calcium carbonate precipitation.

Binding of calcium by organic anions, determined by perturbation of the equilibrium solubility of [14C]calcium oxalate

Confirmation is needed of the reported binding of calcium ions (Ca2+) by bile salts, which is believed to decrease the activity of free calcium ions [Ca2+] available for precipitation of insoluble calcium salts of organic anions in pigment gallstones. We report a new method to determine the association constants (K'f) of calcium for organic anions, from the perturbation by the added anion of the equilibrium solubilization of calcium [14C]oxalate monohydrate crystals (CaOx*). CaOx* crystals were prepared by stepwise conversion of [14C]oxalic acid to its K+ and Ca2+ salts. Structure and purity were confirmed by X-ray diffraction of the crystals. CaOx* was incubated (37 degrees C, under N2) in 0.15 M NaCl in CO2-free deionized H2O at pH 6.3. Dissolution of CaOx*, estimated by radioassay of the 0.22-micron Millipore filtrate, attained equilibrium at 3 days, with K'sp = [Ca2+] * [Ox=] = 2.34 X 10(-8) M2, calculated using known affinity constants for the soluble complexes of NaOx- (K'NaOx = 3.215 M-1) and CaOx (K'CaOx = 195.0 M-1). Keeping total [Na+] = 0.15 M, we added anions that formed soluble complexes with Ca2+. This decreased free [Ca2+], causing more CaOx* to dissolve in amounts related to the concentration of added anion and its K'f for Ca2+. With this method, K'f values for citrate, malonate and malate were similar to the values we determined with the Ca2+ ion electrode, and to published values obtained with the Ca2+ ion electrode and other methods. The sensitivity of the CaOx method permits determination of K'f values with small quantities and low concentrations of the anions and calcium.

Increased biliary calcium in cholesterol and pigment gallstone disease: the role of altered bile acid composition

The present study was undertaken to define the relationship between calcium metabolism and bile acid composition in animal models of diet induced cholesterol and pigment gallstones. Groups of prairie dogs were fed either a control non-lithogenic chow (N = 12), a 1.2% cholesterol enriched chow (N = 6, XOL) for two weeks, or a high carbohydrate diet deficient in iron (N = 6, CHO-FeD), or a high carbohydrate diet with normal iron levels (N = 6, CHO) for eight weeks. Hepatic (HB) and gallbladder (GB) bile samples were analyzed for total calcium, cholesterol, phospholipids, total bile acids (TBA), and individual bile acid composition. In each of the four groups, TBA concentrations were essentially similar and taurine conjugates accounted for approximately 90% of TBA in HB bile and about 98% in GB bile. In the control group, cholic acid (CA) was the predominant bile acid and comprised 76% of TBA and chenodeoxycholic (CDCA) accounted for about 13% of the total. Feeding a diet rich in cholesterol caused a significant change in the relative concentrations of individual bile acids of hepatic bile--such that CA decreased significantly (p less than 0.001) while CDCA increased by 300% (p less than 0.001). The changes in secondary bile acids were insignificant. An identical shift in individual bile acid composition was noted in animals maintained on high carbohydrate diet, irrespective of iron content. Similar changes were observed in the GB in the experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraluminal calcium binding does not mediate fatty acid-induced pancreatic bicarbonate secretion

Since the chain length dependency of fatty acid-induced pancreatic exocrine secretion parallels that of fatty acid-induced inhibition of gastric emptying, similar mechanisms of action may be involved. An earlier study suggested that binding of calcium might mediate fatty acid-induced inhibition of gastric emptying. This study investigated possible mediation of fatty acid-induced pancreatic secretion by calcium binding. Pancreatic secretory response to intraduodenal administration of dodecanoate and various calcium chelators (sodium EDTA, calcium-saturated EDTA, sodium dodecyl sulfate, sodium dioctyl sulfosuccinate, and sodium taurocholate) was studied in three dogs equipped with chronic pancreatic fistulae. Calcium affinity of the various test solutions was quantitated by titrating aliquots of perfusate against a standard CaCl2 solution. Sodium EDTA was found to be the most potent calcium binder (pKc 8.3); sodium dodecanoate, sodium dodecyl sulfate, and sodium dioctyl sulfosuccinate were moderate calcium binders (pKc 7.3, 7.2, 6.9, respectively), whereas sodium taurocholate and calcium-saturated EDTA were poor calcium binders. Sodium dodecanoate evoked brisk bicarbonate output (0.6-1.6 mEq/15 min). Minimal secretory responses were observed in response to all other agents tested. These findings suggest that calcium binding is not involved in mediation of fatty acid-induced pancreatic bicarbonate secretion.