Studies of relationship among bile-acid uptake, Na+, K+-ATPase, and Na+ gradient in isolated cells from rat ileum

Studies were performed to determine relationships among Na+, K+-ATPase, the transmucosal Na+ gradient, and bile-acid transport in metabolically viable cells isolated from rat ileum. Incubation of cells with 0, 10(-6), 10(-5), 10(-4) and 10(-3) M ouabain resulted, respectively, in a 0, 10.3, 42.1, 97.0, and 100% decrease in glycocholate uptake and a 0, 10.7, 46.4, 76.8, and 100% decrease in Na+, K+-ATPase activity. Thus, one-half maximal inhibition of glycocholate uptake and Na+, K+-ATPase activity occurred at 5.5 x 10(-5) M and 1.7 x 10(-5) M ouabain, respectively. A change in glycocholate uptake was correlated with a change in Na+, K+-ATPase activity after daily injections of methylprednisolone. After 4 days treated animals showed a 26% and 36% increase in glycocholate uptake and Na+, K+-ATPase activity, respectively, over pair-fed saline-treated controls (p less than 0.001). Methylprednisolone did not significantly alter the activity of (Mg++)-ATPase when compared with controls (p greater than 0.05). Glycocholate uptake was reduced by the omission of Na+ from the incubation medium. Preincubation of cells at 37 degrees C with gramicidin D, 10 micrograms/ml, to alter membrane permeability to Na+, resulted in a significant rise in cell Na+ (p less than 0.01) and a significant fall in glycocholate uptake from values in untreated cells (p less than 0.01) to approach values for glycocholate uptake at 0 degrees C. These data suggest that Na+, K+-ATPase may play a role in a bile-acid uptake into ileal cells possibly by maintaining a Na+ electrochemical potential gradient for coupled Na+-bile-acid transport.