K+ TRANSPORT IN ISOLATED GUINEA-PIG COLONOCYTES - EVIDENCE FOR NA+-INDEPENDENT OUABAIN-SENSITIVE K+ PUMP

K+ transport mechanisms in epithelial cells isolated from guinea pig distal colon have been studied using Rb-86 as a tracer. A transport pathway has been identified that is proposed to be identical to the mechanism mediating transepithelial K+ absorption. Guinea pig colonocytes take up K+ through at least three separate mechanisms: 1) a Na+-dependent, ouabain-sensitive influx that is consistent with the Na+-K+ pump, 2) a Nac-dependent bumetanide-sensitive influx consistent with the Na+-K+-2Cl(-) cotransporter, and 3) a Na+-independent ouabain-sensitive influx, consistent with an apical colonic K+ pump. These transport mechanisms are sensitive to metabolic inhibition by rotenone and to vanadate, a blocker of type P adenosinetriphosphatase (ATPases). SCH-28080, an inhibitor of gastric K+-H+-ATPase, was without effect. Measurements of net K+ fluxes revealed that isolated colonocytes concentrated K+ by two processes: 1) a Na+-dependent ouabain-sensitive mechanism, which is compatible with the Na+-K+ pump and 2) a Na+-independent ouabain-sensitive mechanism consistent with the proposed absorptive K+ pump. These concentrative mechanisms were also inhibited by rotenone and vanadate, but not by SCH-28080. The Na+-independent ouabain-sensitive K+ pump was present in the distal colon, but absent in the proximal colon and the small intestine of guinea pig. It is proposed that this Na+-independent ouabain-sensitive K+ pump mediates K+ absorption and is related to the luminal K+-ATPase.