TRYPSIN DIGESTION INCREASES NA-H+ EXCHANGE-RATES IN NATIVE RABBIT BRUSH-BORDER MEMBRANE()

Experiments were designed to examine the effects of trypsin-mediated p roteolysis on the activity of the rabbit renal brush border membrane N a+-H+ exchanger. Incubation of brush border membrane vesicles with try psin resulted in a concentration and time-dependent change in proton g radient-stimulated sodium uptake. Extensive trypsin digestion resulted in a marked decrease in the activity of the transporter. By contrast, limited trypsin digestion resulted in a significant increase in proto n gradient-stimulated, amiloride-inhibitable sodium uptake. Sodium-dep endent proton efflux was also significantly increased by limited tryps in digestion. The passive permeability of the vesicles to sodium and p rotons, and the sodium-dependent and sodium-independent uptake of gluc ose were not affected by limited trypsin digestion. These data indicat e that limited trypsin digestion increases the activity of the renal b rush border membrane Na+-H+ exchanger. It is suggested that the renal Na+-H+ exchanger contains one or more inhibitory components or sites w hich are sensitive to inactivation by limited trypsin-mediated proteol ysis.