ABNORMAL NA+ H+ ANTIPORTER PHENOTYPE AND TURNOVER OF IMMORTALIZED LYMPHOBLASTS FROM TYPE-1 DIABETIC-PATIENTS WITH NEPHROPATHY/

Cellular Na+/H+ eschanger (NHE) activity is elevated in type 1 diabeti c patients with nephropathy and patients with essential hypertension. The characteristics of this NHE phenotype in hypertension (raised V-ma x and a lowered Hill coefficient) are preserved in Epstein-Barr virus- transformed lymphoblasts from hypertensive patients. In this study, we have determined NHE kinetics in cultured lymphoblasts from diabetic p atients with and without nephropathy, with nondiabetic controls, using fluorometry with the pH indicator 2,7' bis-(carboxyethyl)-5,6-carboxy fluorescein and estimation of NHE isoform 1 (NHE-1) density with speci fic polyclonal antibodies. The V-max of NHE was elevated significantly , and the Hill coefficient for internal H+ binding was lowered in cell s from patients with diabetic nephropathy compared with both normal co ntrols and normoalbuminuric diabetic patients. NHE-1 density as measur ed by Western blotting was similar in all groups. The turnover number of NHE-1 was thus elevated in cells from nephropathy patients. This ph enotype in cells from diabetic nephropathy patients resembles that in essential hypertension and suggests that such patients may have a pred isposition to hypertension. Moreover, as these changes persist in cult ured lymphoblasts in vitro, these cells should provide a cell culture model to further define the basic mechanisms leading to NHE activation in diabetic nephropathy.