Dependence of cell membrane conductances on bathing solution HCO3-/CO2 in Necturus gallbladder

The effects of bathing solution HCO3-/CO2 concentrations on baseline cell membrane voltages and resistances were measured in Necturus gallbladder epithelium with conventional intracellular microelectrode techniques. Gallbladders were bathed in either low HCO3-/CO2 Ringer's solutions (2.4 mM HCO3-/air or 1 mM HEPES/air) or a high HCO3-/CO2 Ringer's (10 mM HCO3-/1% CO2). The principal finding of these studies was that the apical membrane fractional resistance (fRa) was higher in tissues bathed in the 10 mM HCO3-/CO2 Ringer's, averaging 0.87 +/- 0.06, whereas fRa averaged 0.63 +/- 0.07 and 0.48 +/- 0.08 in 2.4 mM HCO3- and 1 mM HEPES, respectively. Intraepithelial cable analysis was employed to obtain estimates of the individual apical (Ra) and basolateral membrane (Rb) resistances in tissues bathed in 10 mM HCO3-/1% CO2 Ringer's. Compared to previous resistance measurements obtained in tissues bathed in a low HCO3-/CO2 Ringer's, the higher value of fRa was found to be due to both an increase in Ra and a decrease in Rb. The higher values of fRa and lower values of Rb confirm the recent observations of others. To ascertain the pathways responsible for these effects, cell membrane voltages were measured during serosal solution K+ and Cl- substitutions. The results of these studies suggest that an electrodiffusive Cl- transport mechanism exists at the basolateral membrane of tissues bathed in a 10 mM HCO3-/1% CO2 Ringer's, which can explain in part the fall in Rb. The above observations are discussed in terms of a stimulatory effect of solution [HCO3-]/PCO2 on transepithelial fluid transport, which results in adaptive changes in the conductive properties of the apical and basolateral membranes.