Diffusion resistance of endothelium and stroma of bullfrog cornea determined by potential response to K+

Corneas of bullfrog (Rana catesbeiana) were mounted between lucite chambers. A four-electrode system was used and the potential difference (PD) and the electrical resistance were measured. In intact corneas, the PD averaged 25 mV (acqueous side positive) and the electrical resistance 1.5 kQ - cm2. perfusion of the aqueous side with high K+ solutions resulted in a marked decrease in PD and a drop in the electrical resistance. Scraping the epithelium (leaving the stroma plus endothelium) resulted in a drop of the PD to about zero and a decrease in electrical resistance to about 0.1 kQ - CM2 and a very small PD response to a marked elevation of the K+ concentration on the aqueous side. On the basis of the above, it is obvious that the large delta PD in intact corneas, due to elevation of the K+ concentration, must be due to K+ diffusing from the aqueous side across the endothelium and stroma and reaching the epithelium. The duration of the PD response is therefore a measure of the resistance to diffusion of the stroma plus endothelium. A quantitiative analysis shows that under in vitro conditions the resistance of the endothelium plus stroma to the diffusion of ions is very low.