The influence of furosemide and Co2+ on electrolyte and water transport in newt distal tubule and frog skin

The technique of stationary microperfusion of the early distal tubule used in experiments on male newts (Triturus vulgaris) revealed the intratubular effect of CoCl₂ and furosemide on the ion transport. CoCl₂ in concentration 5·10^–4 M increased Na and Cl reabsorption, reduced Ca, Mg and K reabsorption, and increased (TF _exp/TF _o)_in from 1.14±0.04 to 1.68±0.27 (p<0.001). CoCl₂ in concentration 5·10^–5 M enhanced Na and Cl reabsorption, without affecting transport of other ions. 6·10^–4 M furosemide decreased reabsorption of water, Na, Cl, Ca and Mg. The combined effect of Co²⁺ and furosemide inhibited reabsorption of Mg and Ca to a greater extent, but stimulated Na reabsorption. Experiments on frog skin showed that being added to the apical membrane of cells, Co²⁺ stimulates short circuit current and potential differences, whereas furosemide reducing Cl absorption induces only hyperpolarization. Experimental findings allow to assume that Co²⁺ on the outer surface of the apical membrane of the distal tubule cells blocks the selective Ca and Mg channels and activates Na channels.