Lack of PCMB action upon the outer barrier sodium permeability in the absence of Na in toad skin.

The stimulation of apical Na permeability by p-chloromercuribenzoate (PCMB) was evaluated by studying its effect on unidirectional 24Na flux (JNaeff) from inner to outer compartment in the isolated short-circuited toad skin. With Na present in the inner compartment, addition of PCMB to the outer skin surface led to an increase of JNaeff. However, after replacing all Na of the inner compartment by K or choline, the amiloride inhibitable Na permeability of the outer cell membrane increased, and PCMB was no longer effective. It is concluded that PCMB releases the blocking effect of intracellular Na on apical Na channels. If intracellular Na is drastically reduced virtually all Na channels are opened so that PCMB does no longer act.