Fig. 1. Gravimetric measurement of fluid flow (J_v) across Fundulus heteroclitus intestine for time controls (treated with drug vehicle alone) and drug-treated preparations (B) (test; 0.1 mmol l^–1 IBMX + 0.5 mmol l^–1 db-cAMP + 1 µmol l^–1 ionomycin, added at 60 min; arrow in A) from animals before (unfed) or after (fed) daily feeding. Results for a typical experiment appear in A and include control (open symbols) and test (filled symbols) membranes from fed animals. The lines in A are least-squares linear regressions of mass on time. The combined treatment reversed the normal fluid absorption to net fluid secretion in fed animals (P<0.01, Bonferroni post-hoc test following one-way analysis of variance, P=0.005, N=8). In the unfed animals, there was a non-significant trend towards secretion (P>0.05). Values are means + S.E.M., N=8.