Cyclic AMP stimulates ouabain-insensitive ion movement in shark rectal gland

Summary

When the active sodium-potassium pump (Na−K-ATPase) of shark rectal glands is blocked by ouabain, the concentration of intracellular ions changes in the direction of equilibrium with extracellular fluid. These changes were examined when isolated perfused glands were in the basal state and also when they were stimulated to secrete with cAMP and theophylline, to see whether stimulation affected the passive movement of sodium, potassium and chloride across cell membranes. In basal glands 10⁻⁴M ouabain induced an increase of 30 meq/l in intracellular [Na⁺] and a decrease in intracellular [K⁺] of about 50 meq/l after 30 min, while intracellular [Cl⁻] was unchanged. In stimulated glands, these movements were exaggerated. The increase in intracellular [Na⁺] averaged 112 meq/l, and the decrease in intracellular [K⁺], 96 meq/l (P<0.01), while mean intracellular [Cl⁻] rose by 80 meq/l. Furosemide, 10⁻⁴M, partially reversed the accelerated changes in intracellular electrolytes seen after ouabain was added to stimulated glands. These results are consistent with an action of cAMP upon a ouabaininsensitive cotransport of sodium, potassium and chloride in the rectal gland, analogous to that described in avian erythrocytes.