In the small intestine secretagogues stimulate electrogenic Cl- secretion [1] which drives fluid secretion. This Cl- secretion results from the accumulation of intracellular Cl- by a basolateral NaK2Cl cotransporter and the exit of Cl- across the apical membrane via the cystic fibrosis transmembrane conductance regulator (CFTR) [1]. Basolateral K+ channels also play a crucial role in this process by maintaining the driving force for Cl- exit through CFTR, and the K+ channel KCNQ1 is essential to the secretory response stimulated by cAMP-dependent secretagogues [2]. Recently, we demonstrated that in the ileum of the possum, Trichosurus vulpecula, secretagogues stimulate electrogenic HCO3- secretion, not Cl- secretion [3, 4], making this tissue a useful model to investigate the cellular mechanisms of epithelial HCO3- secretion. In the current study we investigated the K+ channels involved in electrogenic HCO3- secretion in the possum ileum. Small intestinal tissue was collected and either used for Ussing chamber measurements of the effects of K+ channel blockers on HCO3- secretion, measurements of K+ channel transcript expression by RT-PCR, or in situ hybridization studies. In the Ussing chamber, the cAMP-dependent secretagogue PGE2 stimulated a sustained increase in short circuit current (Isc) in the ileum, but not the duodenum or jejunum. The generic K+ channel blocker Ba2+ (5 mM serosal, n=8) had no effect on the stimulated Isc. Similarly, serosal 293B (10 µM), a potent inhibitor of KCNQ1 [2] did not inhibit the PGE2-stimulated Isc in the ileum (n=8). Consistent with this, semi-quantitative RT-PCR (n=3) indicated that comparable, low levels of KCNQ1 transcript were expressed in the duodenum, jejunum and ileum. In situ hybridisation (n=3) confirmed that there were low levels of KCNQ1 transcript in the ileal epithelial cells, although there were high levels in the gastric epithelium (n=3). Also, TRAM 34 (10 µM), a potent inhibitor of the K+ channel, KCNN4 [2], had little effect on the PGE2-stimulated Isc (n=8) and there were low levels of transcript for KCNN4 in the ileum (n=3). However, serosal lidocaine (3 mM, n=5), quinidine (1 mM, n=5) and bupivacaine (3 mM, n=5), inhibited the PGE2-stimulated Isc by 19±3%, 24±3% and 50±4%, respectively (P<0.05 compared with controls, Student’s t test). Furthermore, bupivacaine inhibited the Isc stimulated by cpt-cAMP by 53±7% (P<0.05, n=5). This data demonstrates that the K+ channel KCNQ1, which is associated with cAMP-dependent Cl- secretion, is not involved in electrogenic HCO3- secretion in the possum ileum. However, the inhibition of HCO3- secretion by the local anaesthetic bupivacaine and the resistance of the secretory response to Ba2+, suggests that two pore K+ channels are associated with HCO3- secretion.