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

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Abstract
Using conventional and ion selective microelectrodes, the effect of ouabain (10−4 mol/l) on peritubular cell membrane potential (PDpt), on intracellular pH (pHi) as well as on the intracellular ion activities of Cl− (Cl −i ), K+ (K +i ), Na+ (Na +i ) and Ca2+ (Ca 2+i ) was studied in proximal tubules of the isolated perfused frog kidney. In the absence of ouabain (PDpt=−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 PDpt, which is reduced to half (PDpt, 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 PDpt, 1/2 apparent Cl −i increases by 6.2±1.0 mmol/l, pHi by 0.13±0.03, Ca 2+i 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.