This study examined the role of outward K⁺ currents in acinar cell underlying secretion from Brunner's glands in guinea pig duodenum. Intracellular recording were made from single acinar cells in intact acini in in vitro submucosal preparations and videomicroscopy was employed in the same preparation to correlate these measures with secretion. Mean resting membrane potential was -74 mV and was depolarized by high external K⁺ (20mM) and the K⁺ channel blockers 4-AP, quinine and clotrimazole. The cholinergic agonist carbachol (60-2000 nM; EC₅₀=200nM) caused a concentration-dependent initial hyperpolarization of the membrane and an associated decrease in input resistance. This hyperpolarization was significantly decreased by 20 mM external K⁺ or membrane hyperpolarization and increased by 1 mM external K⁺ or membrane depolarization. It was blocked by the K⁺ channel blockers TEA, 4AP, quinine, and clotrimazole but not iberiotoxin. When videomicroscopy was employed to measure dilation of acinar lumen in the same preparation, carbachol-evoked dilations were altered in a parallel fashion when external K⁺ was altered. The dilations were also blocked by the K⁺ channel blockers TEA, 4AP, quinine and clotrimazole but not iberiotoxin. These findings suggest that activation of outward K⁺ currents are fundamental to the initiation of secretion from these glands, consistent with the model of K⁺ efflux from the basolateral membrane providing the driving force for secretion. The pharmacological profile suggests these K⁺ channels belong to the intermediate conductance group.