Trypsin digestion increases Na(+)-H+ exchange rates in native rabbit brush border membrane

Experiments were designed to examine the effects of trypsin-mediated proteolysis on the activity of the rabbit renal brush border membrane Na(+)-H+ exchanger. Incubation of brush border membrane vesicles with trypsin resulted in a concentration and time-dependent change in proton gradient-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 proton gradient-stimulated, amiloride-inhibitable sodium uptake. Sodium-dependent proton efflux was also significantly increased by limited trypsin digestion. The passive permeability of the vesicles to sodium and protons, and the sodium-dependent and sodium-independent uptake of glucose were not affected by limited trypsin digestion. These data indicate that limited trypsin digestion increases the activity of the renal brush border membrane Na(+)-H+ exchanger. It is suggested that the renal Na(+)-H+ exchanger contains one or more inhibitory components or sites which are sensitive to inactivation by limited trypsin-mediated proteolysis.