The Na+/H+ exchangers at the brush border membrane (BBM) and the basolateral membrane (BLM) are each distinct with different kinetic and pharmacologic characteristics. At the BBM, Na+/H+ exchange provides an acid microenvironment necessary for nutrient transport. At the BLM, the Na+/H+ exchanger regulates intracellular pH and cell volume which affect cell growth and repair. This study was designed to determine the effect of burn injury on Na+/H+ exchange at the BBM and BLM of the rat enterocyte. Adolescent Sprague-Dawley rats were divided into control (n = 6) and 20% scald burn groups (n = 6). Using differential centrifugation and percoll density gradient techniques, BBM and BLM vesicles were prepared from the jejunum. 22Na+ uptake was measured using a rapid filtration technique. Initial rate uptake studies showed that the slope of Na+ uptake in BBM (y = 0.06x + 0.12, r2 = 0.99) and BLM (y = 0.075x + 0.1, r2 = 0.99) of the control group was higher (P < 0.05) than that in the burn group (y = 0.0345x + 0.06, r2 = 0.98 and y = 0.056x + 0.01, r2 = 0.99). To determine whether the changes in transport are related to the feeding pattern in burn rats, similar experiments were done in pair-fed animals. The initial rate uptake studies of BBM showed a similarily greater slope of Na+ uptake in pair-fed control animals compared to the burn group (y = 0.043x + 0.06, r2 = 0.99 and y = 0.062x + 0.008, r2 0.98; P < 0.05). A similar relationship was noted for the BLM (y = 0.054x + 0.02, r2 = 0.99 and y = 0.078x + 0.03, r2 = 0.98 for burn and controls, respective; P < 0.05). Kinetic studies showed that the Vmax levels of the Na+/H+ exchanger in BBM and BLM vesicles were decreased (P < 0.05) in the burn group (0.60 ± 0.16 nmol/mg protein/5 sec and 1.00 ± 0.16 mM) compared to controls (0.83 ± 0.02 nmol/mg protein/5 sec and 1.80 ± 0.17 mM). Km values were not significantly different. Na+/H+ exchange in the BBM and BLM of burned rats was decreased compared to controls.
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