Recent studies have demonstrated that chronic potassium loading increases Na-K-ATPase specific activity in kidney tissue and suggest that this enzyme plays a role in renal potassium adaptation. Studies of fluid and electrolyte movement, potential difference (PD), AND Na-K-ATPase were performed in colon and jejunum of the rat in order to further characterize the relationship of Na-K-ATPase to potassium secretion. Experimental rats fed 2.6 meq K/gm diet for 7 days were compared to a control group fed 0.13 meq K/gm. In the colon, chronic potassium loading increased potassium secretion from 0.8 +/- 0.2 to 3.9 +/- 0.9 mueq/min per g tissue (P less than 0.01) and PD from 27 +/- 5.0 to 54 +/- 2.6 mV (P less than 0.001), lumen negative, as Na-K-ATPase increased from 5.0 +/- 0.5 to 11.4 +/- 1.0 muM Pi/mg protein per h (P less than 0.001). In contrast, there was no change in PD, potassium movement, or Na-K-ATPase in the jejunum of potassium-loaded rats. Colonic movement of water, sodium, and chloride was similar in the control and potassium-loaded rats. These results indicate that increased Na-K-ATPase is associated with both increased PD and increased potassium secretion in the colon and provide additional evidence suggesting that Na-K-ATPase may be important in the control of transepithelial potassium movement.