“…The original model proposed for intestine (Nellans, Frizzell & Schultz, 1973) and gallbladder (Cremaschi, H6nin & Ferroni, 1974;Frizzell, Dugas & Schultz, 1975) was similar to that formulated by Crane for Na+-glucose cotransport (Crane, 1962). However, a Na+/H + and C1-/HCO~-double exchange was later revealed in many epithelia with a coupling between Na + and C1-due to cellular pH (Murer, Hopfer & Kinne, 1976;Liedtke & Hopfer, 1977;Petersen et al, 1981;Friedman & Andreoli, 1982;Liedtke & Hopfer, 1982a,b;Baerentsen, Giraldez & Zeuthen, 1983;Aronson & Seifter, 1984;Reuss, 1984). In other epithelia, Na+-CI -cotransport was found to be dependent on K + and to be due in fact to a Na+-K+-2C1 -symport (Frizzell & Field, 1984;Greger, 1984); similar findings were also reported for nonepithelial cells (Geck et al, 1980;Aiton et al, 1981;Ellory et al, 1982;Russell, 1983).…”