The effect of mercury on chloride secretion in the shark (Squalus acanthias) rectal gland

1. Mercuric chloride inhibited chloride secretion in a dose dependent way in isolated perfused rectal glands. The effect was readily apparent at a concentration of 10⁻⁶ M and profound and irreversible at 10⁻⁴ M.2. The dithiol dithiothreitol (DTT) 10⁻² M completely prevented the effect of 10⁻⁶ M mercuric chloride, reduced that at 10⁻⁵M and 10⁻⁴M, and made the inhibition at the latter concentration reversible.3. Two organic mercurials, mersalyl and meralluride, that are effective diuretics in the mammalian kidney, and p-chloromercuribenzoyl sulfonic acid (PCMBS), that has no diuretic activity, had no effect on chloride secretion by the rectal gland.4. The effect of mersalyl was not modified by lowering the pH of the solution perfusing the glands.5. These results indicate that inorganic mercury and organic mercurials do not share the same mechanism of action.6. The absence of an effect of organic mercurials on chloride transport in the rectal gland suggests that its effect on another chloride transporting epithelia, the thick ascending limb of the loop of Henle, is not mediated by inhibition of the chloride cotransporter or Na⁺, K⁺-ATPase, common to both epithelia.