Fig. 8. Establishment of a reversed (negative sign) current (abbreviated as I_K^rev in the text) after apical (a) permeabilisation with nystatin, and the effect of 1 mmol l^–1 sodium azide in K⁺-free basolateral (b) saline at different cell pH values. K32, standard saline (see Materials and methods); Na32, all K⁺ in the saline replaced by Na⁺.