Transport of electrolytes and water across wall of rabbit gall bladder

¹ Institute of Biological Chemistry, University of Copenhagen, Copenhagen, Denmark

Gall bladders of rabbits were studied in vitro in an apparatus which permitted measurement of electrical potential difference, net flux of water, and changes in electrolyte concentrations in mucosal and serosal fluid. Net water flux (mucosa to serosa) was directly proportional to net solute transport (measured as sodium flux) and the transported solution was slightly hypertonic. When mannitol was added to the mucosal fluid, water movement occurred against osmotic gradients often exceeding 80 mosmol/kg. Electrical potential differences were small, but the lumen was invariably positive. Flux ratio determinations indicated active transport of both chloride and sodium but not potassium. When isethionate was substituted for chloride, active bicarbonate absorption was also evident. Anion and cation transport were not independent and no transport occurred when choline was substituted for sodium. The evidence suggests coupled active transport of sodium and the major anions. Water movement is dependent upon active solute transport by means of an undetermined coupling mechanism.