Effect of K+ channels in the apical plasma membrane on epithelial secretion based on secondary active Cl- transport.
Models of epithelial salt secretion, involving secondary active transport of Cl- [9], locate the K+ conductance of the plasma membrane exclusively in the basolateral membrane, although there is considerable experimental evidence to show that many secretory epithelia do have a significant apical K+ conductance. We have used an equivalent circuit model to examine the effect of an apical K+ conductance on the composition and flow rate of the fluid secreted by an epithelium in which secretion is driven by the secondary active transport of Cl-. The parameters of the model were chosen to be similar to those measured in the dog tracheal mucosa when stimulated with adrenaline to secrete. We find that placing a K+ conductance in the apical membrane can actually enhance secretion provided the proportion of the total cell K+ conductance in the apical membrane is not greater than about 60%, the enabling effect on secretion being maximal when the proportion is around 10-20%. We also find that even when the entire cell K+ conductance is located in the apical membrane, the secreted fluid remains relatively Na+ rich. Analysis of the sensitivity of model behavior to the choice of values for the parameters shows that the effects of an apical K+ conductance are enhanced by increasing the ratio of the paracellular resistance to the transcellular resistance.
Cook
D I
DI
Department of Physiology, University of Sydney, New South Wales, Australia.
Young
J A
JA
D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism*; D007365:Intercellular Junctions / Q000378:metabolism; D008954:Models, Biological; D015221:Potassium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002712:Chlorides; D015221:Potassium Channels; D000254:Sodium-Potassium-Exchanging ATPase