ELEVATED ERYTHROCYTE SODIUM-LITHIUM COUNTERTRANSPORT ACTIVITY CORRELATES WITH INCREASED INTRACELLULAR SODIUM AND FREE CALCIUM-ION CONCENTRATION IN TYPE-2 DIABETES

To explore the mechanism by which elevated sodium-lithium countertrans port activity (SLC) associates with both predisposition to hypertensio n and diabetic nephropathy, we investigated the interrelationships amo ng SLC, intracellular sodium concentration ([Na]i), intracellular free calcium-ion concentration ([Ca2+]i), diabetic nephropathy, hypertensi on, family history of hypertension, and other factors in 48 patients w ith Type 2 diabetes and 24 healthy controls. There was a significant c orrelation between SLC and [Na]i (r = 0.36, p < 0.05), [Na]i and [Ca2]i (r = 0.47, p < 0.01), SLC and [Ca2+]i (r = 0.46, p < 0.01), and bet ween HbA(1c) and [Ca2+]i (r = 0.38, p < 0.01). Both [Na]i and [Ca2+]i were significantly higher in the patients with elevated SLC than in th ose with normal SLC (p < 0.01 and p < 0.05, respectively). In stepwise multivariate regression analysis, [Na]i, HbA(1c), and SLC appeared as independent determinants of [Ca2+]i. These data suggest a significant correlation of elevated SLC with increased [Na]i and [Ca2+]i. This ma y be a possible mechanism underlying the close association of elevated SLC with both predisposition to hypertension and diabetic nephropathy .