Effects of bicarbonate on fluid and electrolyte transport by the guinea pig gallbladder: A bicarbonate-chloride exchange

Summary Fluid transport and net fluxes of Na, K, Cl and HCO₃ by guinea pig gallbladder were investigatedin vitro. A perfused gallbladder preparation was devised to simultaneously study unidirectional fluxes of²²Na and³⁶Cl. The net Cl flux exceeded the net Na flux during fluid absorption in the presence of HCO₃. This Cl excess was counter-balanced by a net HCO₃ secretion: a HCO₃–Cl exchange. PGE₁ reversed the direction of fluid transport and abolished the net Cl flux. The magnitude of the HCO₃ secretion remained unchanged, but shifted from a HCO₃–Cl exchange to a net secretion of NaHCO₃ and KHCO₃. Furosemide inhibited both the HCO₃–Cl exchange and HCO₃ secretion after PGE₁ without influencing fluid absorption. Ouabain inhibited the HCO₃–Cl exchange as well as fluid absorption; only the effect on the HCO₃ secretion was entirely reversible. Secreted HCO₃ appeared not to be derived from metabolic sources since HCO₃ secretion was abolished in a HCO₃-free bathing medium. HCO₃ secretion was also dependent on the Na concentration of the bathing fluid. Three lines of evidence are presented in favor of an active HCO₃ secretion in guinea pig gallbladder. HCO₃ is secreted against: (i) a chemical gradient, (ii) an electrical gradient and (iii) the direction of fluid movement under control conditions.