Intracellular Cl activity changes of frog skin.

The intracellular Cl activity and potential were determined in short-circuited frog skin with single-barrel microelectrodes. With NaCl Ringer solution on the apical and basolateral side, the intracellular Cl activity was 15.5 +/- 0.5 mM and the intracellular potential was -90 +/- 1.0 mV, indicating that the intracellular Cl activity was above electrochemical equilibrium. When the solution on the apical side was changed to a Cl-free solution (Cl replaced by methanesulfonate), no significant difference was observed in intracellular Cl activity. However, when the skins were Cl-depleted by replacing the NaCl Ringer solution on both sides with a Cl-free solution, the intracellular Cl activity decreased to 1.7 +/- 0.1 mM and the intracellular potential fell to -66.7 +/- 1.3 mV. Addition of Cl (i.e., NaCl Ringer solution) to the apical side of Cl-depleted skins caused a significant increase in intracellular Cl activity to 6.3 mM. This increase was prevented by amiloride (10(-4) M) added on the apical side simultaneously with Cl. Restoration of Cl on the basolateral side of Cl-depleted tissues also raised the intracellular Cl activity to about the same level as when Cl was added on the apical side (6.8 mM). Changes in membrane potential occurred in a delayed fashion over a period of 15 min or more when Cl was added or removed on either side of the skin. The absence of an immediate membrane potential response indicates that Cl conductance is not detectable. We conclude, therefore, that the Cl transfer across the apical and basolateral cell membrane occurs primarily via electroneutral mechanisms.