Studies on chloride permeability of the skin of Leptodactylus ocellatus: III. Na+ and Cl- effect on electrical phenomena.

During their flux through the skin of the frog Leptodactylus ocellatus, Na+ and Cl- interact with each other. This interaction gives rise to electrical phenomena which are studied in the present paper. The skin is mounted in Na2SO4 Ringer's with 115 mM Na+ on the inside, and a variety of outer solutions. The osmolarity of all solutions is kept constant at 237.8 mosmol by adding sucrose. When the main anion used on the outside is SO=4 the electrical potential difference (deltapsi) rises steadily with the concentration of sodium (Na+)0 up to 87 mV, which is reached at about 20 mM. Thereafter deltapsi remains constant. When the main anion is Cl- it is observed that deltapsi rises steadily with (NaCl)0 with a slope similar to the curve obtained with SO=4 (37 mV per decade), but with a lower intercept attributed to an inward Cl pumping which is characteristic of this frog species. At 2--9 mM (NaCl)0 a Cl-specific channel is activated. Further increases of (NaCl)0 produce a decrease of deltapsi. The specificity of the activation of this site by monovalent cations and its use by monovalent anions is also studied.