In vitro studies of theophylline-induced changes in Na, K and Cl transport in hen (Gallus domesticus) colon suggesting bidirectional, basolateral NnK2Cl cotransport

1. 1. In isolated mucosa from a NaCl-loaded hen theophylline stimulates both unidirectional chloride fluxes (J^Cl_msand J^Cl_ms). Conductive and electroneutral exchange processes, besides a bumetanidesensitive, rheogenic process contribute. 2. 2. The bumetanide-sensitive fraction of the theophylline-induced ΔJ^Cl_ms is sodium-dependent. 3. 3. Incubation in nominally K⁺-free solutions reduces the bumetanide-sensitive fraction ΔJ^Cl_ms more than treatment with ouabain. 4. 4. With respect to chloride the bumetanide-sensitive fraction of ΔJ^Cl_ms has a Hill coefficient of 1.93 ± 0.03, a J_max of 12.9 ± 0.2 μmol/cm²·hr and a K 1 2 of 73 ± 1 mmol/l. 5. 5. After ouabain treatment ΔJ_ms^Cl and ΔJ_ms^Cl are equally sensitive to bumetanide, while ΔJ_ms^Cl is bumetanide insensitive without ouabain treatment.