Methyl mercury inhibits short-circuit current and Cl − influx across isolated epipodite of European lobster ( Homarus gammarus)

Abstract

The effect of methyl mercuric chloride (MeHg) on short-circuit current ( I SC) was studied in the isolated perfused epipodite preparation from the branchial chamber of European lobster ( Homarus gammarus) acclimated to dilute seawater. When applied at the apical surface, 0.2, 1.0 and 3.0 μM MeHg depressed I SC by a 26%, 81% and 98%, respectively. The half-maximal inhibitory concentration (IC 50) of apically applied MeHg was 0.6 μM. Basolaterally added MeHg (3.0 μM) had no effect on I SC, whereas addition of the specific Na +,K +-ATPase inhibitor ouabain (1.5 mM) reduced I SC by ∼ 90%. Ouabain effects were reversible, and I SC fully recovered upon removal of ouabain. The MeHg-induced block of I SC was partially reversed by the reducing agent, 1,4-dithiothreitol, suggesting that the formation of S–Hg–S bridges is important in the inhibitory mechanism. A significant reduction of I SC and conductance occurred when low Na + and Cl − salines were substituted. Furthermore, in the low Na + saline, J Cl A → B fluxes were reduced by about 50%. In the highly conductive epipodite epithelium, coupling of Na + and Cl − fluxes was suggested. The effects of MeHg on I SC in the lobster epipodite are attributed to inhibition of an apical Cl − influx.