Effects of inhibitors on 3-O-methylglycose transport in rabbit ileum

Summary Previous studies (Goldner, Schultz & Curran,J. Gen. Physiol. 1969,53:362) have suggested a direct coupling between influxes of sugars and Na across the brush border membrane of rabbit ileum. Effects of several inhibitors, ouabain, cyanide, dinitrophenol and iodoacetate on 3-O-methylglucose fluxes were examined in an effort to obtain information about coupling of sugar transport to metabolism. The inhibitors virtually abolished net active sugar transport across the whole tissue but had less striking effects on sugar influx across the brush border membrane, particularly when the cells were prevented from gaining Na as a result of inhibitor action. However, substantial but incomplete inhibition of influx was observed when the cells were permitted to gain Na. Mucosal strips incubated with ouabain to elevate cellular Na extruded sugar against a concentration gradient when cell Na concentration exceeded that in the medium. Conversely, a small extrusion of Na from ouabain-poisoned cells was observed in the presence of an outwardly directed concentration gradient for sugar. These results provide further evidence of coupling between Na and sugar movement. Additional direct coupling of sugar movement to metabolism cannot be ruled out.