The effect of ouabain on intracellular activities of K+, Na+, Cl−, H+ and Ca2+ in proximal tubules of frog kidneys

Using conventional and ion selective microelectrodes, the effect of ouabain (10^–4 mol/l) on peritubular cell membrane potential (PD_pt), on intracellular pH (pH_i) as well as on the intracellular ion activities of Cl^– (Cl _i ^– ), K⁺ (K _i ⁺ ), Na⁺ (Na _i ⁺ ) and Ca²⁺ (Ca _i ²⁺ ) was studied in proximal tubules of the isolated perfused frog kidney. In the absence of ouabain (PD_pt=–57.0±1.9 mV), the electrochemical potential difference of chloride (apparent {ie6-1} and of potassium {ie6-2} is directed from cell to bath, of H⁺ {ie6-3}, of Na⁺ {ie6-4} and of Ca²⁺ {ie6-5} from bath to cell. Ouabain leads to a gradual decline of PD_pt, which is reduced to half (PD_{pt, 1/2}) within 31±4.6 min (in presence of luminal glucose and phenylalanine), and to a decline of the absolute values of apparent {ie6-6}, of {ie6-7}, {ie6-8} and {ie6-9}. In contrast, an increase of {ei6-10} is observed. At PD_{pt, 1/2} apparent Cl _i ^– increases by 6.2±1.0 mmol/l, pH_i by 0.13±0.03, Ca _i ²⁺ by 185±21 nmol/l, and Na _i ⁺ by 34.2±4.6 mmol/l, whereas K _i ⁺ decreases by 37.7±2.2 mmol/l. The results suggest that the application of ouabain is followed by a decrease of peritubular cell membrane permeability to K⁺, by an accumulation of Ca²⁺, Na⁺ and HCO ₃ ^- in the cell and by a dissipation of the electrochemical Cl^– gradient.Supported by Österr. Forschungsrat, Proj. No. 4366