Demonstration of net potassium absorption in mammalian colon.

The present in vivo studies were performed in the rat to determine whether the colon was capable of net potassium absorption, as well as secretion, and to further elucidate the process responsible for net potassium movement. Both the proximal and distal lumina of the colon of control, potassium-deficient, and potassium-loaded animals were perfused with solutions containing either 140 or 20 mmol/l sodium. Net potassium secretion was present in both proximal and distal colon of control animals during perfusion with the 140 mmol/l sodium solution. The rate of net potassium secretion was reduced in the potassium-deficient animals. During perfusion with the 20 mmol/l sodium solution, the rate of potassium secretion was also reduced (compared with control perfusion solution) in both the control and potassium-deficient animals. As a result, there was net potassium absorption (0.94 +/- 0.14 mueq.1-1.g dry wt-1) and zero net potassium movement in the distal and proximal segments, respectively, of the potassium-deficient animals perfused with the low-sodium solution. Additional studies were performed to determine whether net potassium secretion was saturable and showed that, during progressive increases in the plasma potassium level, net secretion was constant at plasma potassium levels above 11-13 meq/l. These data, therefore, demonstrate that the mammalian colon regulates intestinal transport of potassium by both absorptive and secretory mechanisms and that a carrier-mediated process probably regulates both transport processes.