Uncoupled basal sodium absorption and chloride secretion in prairie dog (Cynomys ludovicianus) gallbladder

1. Prairie dog gallbladders mounted in a Ussing-type chamber and bathed with symmetrical Ringer's solutions exhibited a transepithelial resistance (Rt) of 51 +/- 5 omega cm2, a lumen negative potential difference (Vms) of 11.5 +/- 0.7 mV and a short-circuit current (Isc) of 6.9 +/- 0.3 microEq/hr/cm2. 2. Radioisotopic ion flux experiments revealed that the basal Isc of 6.9 +/- 0.3 microEq/hr/cm2 was mostly accounted for by net Na+ absorption of 3.2 +/- 0.5 microEq/hr/cm2 and net Cl- secretion of 2.9 +/- 0.3 microEq/hr/cm2. 3. In HCO3- free Ringer's, net Na+ flux was virtually abolished, net Cl- flux decreased by 50% and Isc was reduced by 77%. 4. 10(-3) M mucosal amiloride and DIDS reduced Isc by 28 and 24%, respectively. 5. Mucosal NaCl diffusion potentials indicated that the paracellular pathway was cation selective. 6. Thin section electron micrographs showed a single cell population in this epithelium suggesting that net Na+ absorption and Cl- secretion may emerge from the same cells. 7. We conclude that prairie dog gallbladder epithelium is an electrogenic tissue and, in contrast to gallbladders of most other species, simultaneously but independently absorbs Na+ and secretes Cl-.