“…Intrinsic regulation of Na+ channels is governed by various factors including changes in the composition of the extracellular fluid, in cell volume, in cell metabolism or, the essence of this study, in Na+ transport load (Zeiske & Van Driessche, 1984;Sariban-Sohraby & Benos, 1986). Several lines of evidence have clearly demonstrated an inverse relationship between the concentration of mucosal Na+ and the apical membrane Na+ permeability in frog skin (Fuchs, Larsen & Lindemann, 1977) and many other tight epithelia (reviewed by Wills & Zweifach, 1987;Garty & Benos, 1988;Smith & Benos, 1991 Lewis, Ifshin, Loo & Diamond, 1984;Ling & Eaton, 1989). On the other hand, using patch clamp, Palmer & Frindt (1988) failed to observe any change in the number of active channels by external Na+ in rat cortical collecting tubules.…”