Na+ and K+ transport at basolateral membranes of epithelial cells. I. Stoichiometry of the Na,K-ATPase.
The stoichiometry of pump-mediated Na/K exchange was studied in isolated epithelial sheets of frog skin. 42K influx across basolateral membranes was measured with tissues in a steady state and incubated in either beakers or in chambers. The short-circuit current provided estimates of Na+ influx at the apical membranes of the cells. 42K influx of tissues bathed in Cl- or SO4-Ringer solution averaged approximately 8 microA/cm2. Ouabain inhibited 94% of the 42K influx. Furosemide was without effect on pre-ouabain-treated tissues but inhibited a ouabain-induced and Cl--dependent component of 42K influx. After taking into account the contribution of the Na+ load to the pump by way of basolateral membrane recycling of Na+, the stoichiometry was found to increase from approximately 2 to 6 as the pump-mediated Na+ transport rate increased from 10 to 70 microA/cm2. Extrapolation of the data to low rates of Na+ transport (less than 10 microA/cm2) indicated that the stoichiometry would be in the vicinity of 3:2. As pump-mediated K+ influx saturates with increasing rates of Na+ transport, Na+ efflux cannot be obligatorily coupled to K+ influx at all rates of transepithelial Na+ transport. These results are similar to those of Mullins and Brinley (1969. Journal of General Physiology. 53:504-740) in studies of the squid axon.
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D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011894:Rana pipiens / Q000378:metabolism; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007473:Ion Channels; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium