Previous evidence supports a role for prostaglandin E₂ (PGE₂) in carbachol (CCh)-induced changes in short-circuit current (∆ISC⁾ in rat distal colon (Bellingham et al, 2002). Since PGE₂ results from arachidonic acid (AA) metabolism, we have now further examined the role of this pathway in CCh-induced ∆I.Terminal colon (5cm) was removed from male Wistar rats killed humanely by cervical dislocation, and the mucosal/submucosal portion mounted in an Ussing chamber. Both sides of the tissue were bathed in Krebs solution at 37°C and gassed with 95%O₂/5%CO₂. ∆I was measured and values represent mean ± S.E.M. Student′s t-test was used to test significance (P<0.05 considered significant). Mean basal I_SCwas 10.5 ± 2.0 µA cm^-2 (n=26). CCh (100 µM basolateral) induced a triphasic ∆I_SC consisting of an increase in I_SC (phase 1) then a decrease in I_SC,followed by a maximal increase in I_SC (phase 3). Inhibiting AA liberation with the PLA₂ inhibitor aristolochic acid (100 µM basolateral) did not affect basal I_SC but reduced phase 3 of the CCh-induced ∆I_SC from 81.2 ± 12.6 µA cm^-2 to 18.3 ± 14.3 µA cm^-2 (n=3, P<0.02, paired t-test). Phases 1 and 2 were unaffected. Since AA can also be produced from diacylglycerol (DAG), we examined the effect of the DAG lipase inhibitor RHC 80267 (100 µM basoalteral and apical) on the CCh-induced ∆ISC^. RHC 80267 decreased basal I_SC by 7.5 ± 1.7 µA cm^-2 and reduced phase 3 of the CCh-induced ∆Ifrom 50.8 ± 8.7 µA cm^-2 to 19.6 ± 2.9 µA cm^-2(n=6, P<0.05, paired t-test, Fig 1A) but had no effect on phases 1 or 2. AA (100 µM basolateral and apical) increased basal I_SC by 13.6 ± 8.4 µA cm^-2(n=4, P<0.05, unpaired t-test) in the same manner as PGE₂ increased basal I_SC (Bellingham et al, 2002). The total I_SC produced by addition of AA (or PGE₂) and CCh was the same as that caused by CCh alone (n=4, P<0.05, paired t-test, Fig 1B).AA and its metabolites such as PGE₂ play a role in regulation of epithelial ion secretion (DÖring et al, 1990; Carew and Thorn, 2000; Hosoda et al, 2002). Here we provide further evidence supporting the involvement of AA metabolism in CCh-induced ∆I_SC in the rat colon.