EFFECTS OF MERCURIC-CHLORIDE ON THE RESTING MEMBRANE-POTENTIALS OF BLUE-CRAB (CALLINECTES-SAPIDUS) MUSCLE-FIBERS

The effects of concentrations of mercuric chloride ranging from 3.68 to 368 μM (1-100 ppm) on the resting membrane potentials of muscle fibers in the extensor muscle of the carpopodite in walking legs of adults blue crabs were investigated in vitro. Glass micropipettes filled with saturated solutions of potassium chloride and conventional electronic equipment were used. Resting membrane potentials in uncontaminated artificial sea water averaged -78 mV ± 4 mV (S.E.M.). Mercuric chloride added to the control bath at 3.68 or 9.2 μM did not affect the resting membrane potentials. At 18.4 μM threshold effects were obtained in 50% of the preparations. At concentrations ranging from 25.7 to 368 μM progressive deterioration of membrane polarization occurred as the mercury concentration was increased. This effect was irreversible despite multiple washes with normal sea water. We conclude that mercuric chloride has very powerful toxic effects at the peripheral motor effector elements in blue crabs. These results do not, of course, rule out more central effects on enzymatic systems or neuronal networks. © 1979.