Na+ and K+ transport at basolateral membranes of epithelial cells. II. K+ efflux and stoichiometry of the Na,K-ATPase.
Changes of 42K efflux (J23K) caused by ouabain and/or furosemide were measured in isolated epithelia of frog skin. From the kinetics of 42K influx (J32K) studied first over 8-9 h, K+ appeared to be distributed into readily and poorly exchangeable cellular pools of K+. The readily exchangeable pool of K+ was increased by amiloride and decreased by ouabain and/or K+-free extracellular Ringer solution. 42K efflux studies were carried out with tissues shortcircuited in chambers. Ouabain caused an immediate (less than 1 min) increase of the 42K efflux to approximately 174% of control in tissues incubated either in SO4-Ringer solution or in Cl-Ringer solution containing furosemide. Whereas furosemide had no effect on J23K in control tissues bathed in Cl-rich or Cl-free solutions, ouabain induced a furosemide-inhibitable and time-dependent increase of a neutral Cl-dependent component of the J23K. Electroconductive K+ transport occurred via a single-filing K+ channel with an n' of 2.9 K+ efflux before ouabain, normalized to post-ouabain (+/- furosemide) values of short-circuit current, averaged 8-10 microA/cm2. In agreement with the conclusions of the preceding article, the macroscopic stoichiometry of ouabain-inhibitable Na+/K+ exchange by the pump was variable, ranging between 1.7 and 7.2. With increasing rates of transepithelial Na+ transport, pump-mediated K+ influx saturated, whereas Na+ efflux continued to increase with increases of pump current. In the usual range of transepithelial Na+ transport, regulation of Na+ transport occurs via changes of pump-mediated Na+ efflux, with no obligatory coupling to pump-mediated K+ influx.
T C
TC
Cox
S I
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Helman
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002451:Cell Compartmentation; D004058:Diffusion; D004848:Epithelium / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011898:Ranidae / Q000378:metabolism; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007473:Ion Channels; D010042:Ouabain; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium