Effect of the composition of the inner bathing solution on transport properties of the frog skin

Abstract

1. 1. Electrical parameters and unidirectional Na + fluxes were measured in isolated frog skin bathed by Ringer's solutions of different composition. Since the attention was focused on changes elicited by modifications of the inner bathing Ringer, the composition of the outer solution was usually kept constant, i.e. isotonic Ringer with 50 mM NaCl. 2. 2. The reduction of the concentration of NaCl on the inside from 115 mM to 10 mM (keeping the osmolarity constant) produces a marked decrease of the short circuit current (SCC), electrical potential difference (Δψ) and electrical conductance (χ), with an inflection point around 50 mM. This position of the inflection point is not appreciably shifted by using Ringers with 30, 50 or 80 mM NaCl on the outside, or by replacing Cl − with SO 4 2−, or by making the Ringers hypertonic. 3. 3. The decrease of SCC caused by the reduction of NaCl from plasma levels (115 mM) is due to reductions of the Na + influx and of the Cl − efflux. 4. 4. Although the decrease of the concentration of Na + and of Cl −, and the increase of the effective osmolarity of the inner bathing solution, can elicit a drop of SCC individually, the maximal decrease of SCC is obtained when the three factors act together, i.e. when NaCl is replaced by an equivalent amount of sucrose. 5. 5. Under physiological conditions the concentration of NaCl of the inner bathing solution is close to 115 mM, and the concentration of the outer solution is much lower. In experiments in vitro it is general practice to reduce the concentration of the inner bathing solution in order to study ion penetration in the absence of concentration gradients. The present results indicate that under these circumstances part of the observed kinetics may be due to effects elicited by changes of the inner solution.