Secretion of nitrate by rectal gland of Squalus acanthias.

1. Rectal glands secrete nitrate at 30% of their capacity to secrete chloride. 2. Nitrate secretion is directly related to its concentration at constant chloride concentrations. 3. Chloride has a biphasic effect on nitrate secretion. 4. Hill coefficients at chloride < 100 mM are equal to 1, while at 100 mM indicate inhibition of nitrate by chloride. 6. Lineweaver-Burk plots at chloride < 100 indicate a single site, while at 100 mM indicate inhibition of nitrate by chloride. 7. Bumetanide inhibits nitrate secretion. 8. The data suggest that nitrate interacts with one of the two chloride sites of the chloride transporter.