Pump-leak parallelism in sodium-absorbing epithelia: the role of ATP-regulated potassium channels.

ABSTRACT

In all Na(+)-absorbing and Cl(-)-secreting epithelia, an increase in the activity of the Na+,K(+)-pump at the basolateral membrane is accompanied by an increase in the K+ conductance of that barrier and vice versa. We have recently identified an ATP-regulated K+ channel, K(ATP), in basolateral membrane vesicles isolated from Necturus maculosa small intestinal epithelial cells that could be responsible for this parallelism between pump activity and leak. Thus, an increase in pump activity would result in a decrease in local ATP activity and an increase in local ADP activity and, in turn, an increase in the open-probability of the channel whereas a decrease in in pump activity would have the opposite effect. Further, the likelihood that the number of pumps far exceeds the number of leaks per unit area of membrane suggests that the ATP and ADP activities that influence K(ATP) channel activity may differ markedly from the "bulk" cytoplasmic values.