PUMP-LEAK PARALLELISM IN SODIUM-ABSORBING EPITHELIA - THE ROLE OF ATP-REGULATED POTASSIUM CHANNELS

In all Na+-absorbing and Cl--secreting epithelia, an increase in the a ctivity of the Na+,K+-pump at the basolateral membrane is accompanied by an increase in the K+ conductance of that barrier and vice versa. W e have recently identified an ATP-regulated K+ channel, K-(ATP), in ba solateral membrane vesicles isolated from Necturus maculosa small inte stinal epithelial cells that could be responsible for this parallelism between pump activity and leak. Thus, an increase in pump activity wo uld result in a decrease in local ATP activity and an increase in loca l ADP activity and, in turn, an increase in the open-probabilty of the channel whereas a decrease in pump activity would have the opposite e ffect. Further, the likelihood that the number of pumps far exceeds th e number of leaks per unit area of membrane suggests that the ATP and ADP activities that influence K-(ATP) channel activity may differ mark edly from the ''bulk'' cytoplasmic values. (C) 1997 Wiley-Liss, Inc.