Effect of mercuric chloride on electrical parameters and anion fluxes in the toad skin

The amphibian skin, widely used for studying the transepithelial passage of electrolytes, exhibits anion pathways relatively specific for Cl−. We studied the effect of HgCl2, 1.0×10−4 M on its electrical parameters and unidirectional anion fluxes. In the presence of Cl−, the transepithelial conductance (G) of the isolated skin of the Bufo arenarum toad increased considerably following exposure to HgCl2, whereas short-circuit current (SCC)-reflecting transepithelial Na+ transport-underwent only slight stimulation. Following the blockade of Na+ intake by amiloride, 1.0×10−4 M, the removal of Cl− from the solution bathing the epidermal border of the skin brought about a decrease in G, and gave rise to a gradient-induced SCC (SCCg) consistent with transepithelial passage of Cl− along its gradient. Addition of mercaptoethanol, 5.0×10−3 M to the bath containing Hg2+ fully reversed these effects. The increase in G was accompanied by an increase in the unidirectional (epidermal to dermal) fluxes of 36Cl− and 131I−, and a decrease in the passage of 99mTcO4−. These results show the effects of HgCl2 to be similar to those of theophylline, although exhibiting a different selectivity. Our data suggest that anion passage following exposure to HgCl2 is, like that stimulated by theophylline, predominantly if not exclusively transcellular, and does not involve a significant opening of the tight junctions.