Effects of bicarbonate on the potential difference across the rabbit corneal endothelium

The electrical potential difference across the rabbit corneal endothelium is dependent on the concentration of HCO-3 in the bathing solution. When the HCO-3 was present only on the stromal side, the average normal potential difference of 570 +/- 20 microV (n = 18, aqueous negative) was observed. On the other hand, when the HCO-3 was present only on the aqueous side, the average potential difference was 124 +/- 11 microV (n = 8). By replacing NaHCO3 in the solution with NaCl and KHCO3 with KCl, the potential difference was 32 +/- 7 microV (n = 16). The potential difference reached no saturation level but increased as a function of increasing ambient [HCO-3] up to 70 mM while the electrical resistance remained constant. The near abolishment of the potential difference in the absence of HCO-3 in the solution suggests that endogenous as well as exogenously generated CO2 from air may play at most a minor role in generation of the potential difference. A model to explain the results observed is proposed.