Calcium and carbonate ion concentrations in gallbladder and hepatic bile

Calcium carbonate is a major component of gallstones, but there are few data on calcium and carbonate (CO3(2-)) concentrations in human bile. Therefore, in patients undergoing cholecystectomy for gallstones, total [CaTOT] and free ionized [Ca2+] calcium concentrations, pH, PCO2, and total [CO2] were measured and [CO3(2-)] was derived in gallbladder and hepatic bile (aspirated anaerobically at surgery or from T tubes). Gallbladder bile had lower pH (6.96 vs. 7.30) and total [CO2] (14.1 vs. 21.6 mmol/L), higher PCO2 (53.8 vs. 40.2 mm Hg), lower [CO3(2-)] (2.52 vs. 6.11 x 10(5) mol/L) and lower [Ca2+] x [CO3(2-)] ion product (1.88 vs. 4.74 x 10(-8) mol/L) than did hepatic bile. Gallbladder bile pH correlated positively with total [CO2], [CO3(2-)], and [Ca2+] x [CO3(2-)] but negatively with PCO2. Patients with surface gallstone calcification had similar gallbladder bile [CaTOT] and [Ca2+] but higher gallbladder bile pH (7.30 vs. 6.90), lower PCO2 (42.9 vs. 57.2 mm Hg), higher [CO3(2-)] (7.29 vs. 1.84 x 10(-5) mol/L), and higher [Ca2+] x [CO3(2-)] ion product [4.73 vs. 1.45 x 10(-8) (mol/L)2] than those with radiolucent gallstones. There were no differences in these parameters between patients with cholesterol stones and those with pigment stones. These data suggest that the human gallbladder acidifies bile by secreting hydrogen ion and that impairment of this secretion is one cause of calcified gallstone formation in humans.