The neurosecretory effect of ouabain on isolated rabbit ileal mucosa

Ouabain, when added to fluid bathing rabbit ileal mucosa mounted in a flux chamber, transiently increases short circuit current, implying a paradoxical secretory response. To determine the cause of this change, we studied unidirectional fluxes of 36Cl and 23Na and the effects of ion substitution, of reduced Ca concentration, verapamil, tetrodotoxin and atropine. Ouabain 0.1 mM, transiently increased the serosal to mucosal flux of Cl and Na, increased Isc and PD and reduced ion conductance. The Isc response to ouabain was diminished by reducing the bath fluid concentration of Cl, of Ca, and by adding verapamil. Tetrodotoxin both delayed and reduced the maximal Isc response; atropine had no effect. We conclude that ouabain acts by releasing a neurotransmitter of unknown identity and by increasing the serosal to mucosal flux of Cl.