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 86Rb 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 Na(+)-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.
Instituto Venezolano de Investigaciones Científicas, Centro de Biofísica y Bioquímica, Caracas.
J R
JR
Del Castillo
M C
MC
Súlbaran-Carrasco
L
L
Burguillos
D000818:Animals; D001692:Biological Transport; D002469:Cell Separation; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D006168:Guinea Pigs; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*
D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium