Chloride conductance and mitochondria-rich cell density in isolated skin of Rana catesbeiana acclimated to various environments

The Cl⁻ conductance in isolated skin of frogs (Rana catesbeiana) acclimated to 30 mM solutions of NaCl, Na₂SO₄, MgCl₂ and distilled water (DW) was studied. Transepithelial potential difference (PD_trans), short-circuit current (I_SC) and total conductance (G_t) were measured under conditions such that there was Cl⁻ flux in the presence and absence of Na⁺ transport. The Cl⁻ content of the mucosal solution was acutely replaced with SO₄²⁻ or gluconate to evaluate the effect of removal of Cl⁻ conductance on electrophysiological parameters. Mitochondria-rich cell density (D_MRC) was also measured. Skins from frogs acclimated to NaCl and Na₂SO₄ showed the lowest and the highest D_MRC, respectively, but no difference could be found between the skins from frogs acclimated to DW and MgCl₂ indicating that D_MRC is not unconditionally dependent on environmental Cl⁻ in this species. Frogs acclimated to NaCl showed marked differences when compared to the other groups: the highest G_t, probably represented by a higher paracellular conductance; the lowest transepithelial electrical potential difference which remained invariant after replacement of mucosal Cl⁻ with SO₄²⁻ or replacement of mucosal Cl⁻ with gluconate and an inwardly oriented positive current in the absence of bilateral Na⁺.