KINETIC-PROPERTIES OF ERYTHROCYTE NA-LI+ AND NA+-H+ EXCHANGE IN HYPERTENSIVE PATIENTS()

Objective: To ascertain the relationships between the kinetic properti es of erythrocyte Na+-H+ exchange [maximum kinetic energy (V-max), Mic haelis constant (K-m) for internal H+ and Hill's coefficient], Na+-Li (V-max and K-m for external Na+), and metabolic parameters in normote nsive controls and hypertensive subjects. Materials and methods: Na+-H + exchange was measured as the Na+ influx driven by intracellular H+, and Na+-Li+ exchange as the Li+ efflux driven by extracellular Na+, in erythrocytes from normotensive (n = 59) and hypertensive (n = 93) sub jects. Results: In comparison with normotensives, the hypertensives ha d a higher V-max for Na+-Li+ and Na+-H+ exchange, a higher K-m for ext ernal Na+ for Na+-Li+ exchange and a lower reduced Hill's number for N a+-H+ exchange. V-max values for Na+-Li+ and Na+-H+ exchange were sign ificantly correlated, as were K-m values for internal H+ for Na+-H+ ex change and K-m for external Na+ for Na+-Li+ exchange. Insulin resistan ce and beta-cell function indices were higher in the hypertensives tha n the normotensives. Upon stepwise multiple regression analysis, V-max for Na+-Li+ exchange was correlated significantly and independently w ith K-m for external Na+ and with the insulin resistance index, while K-m for external Na+ was correlated with K-m for internal H+, V-max fo r Na+-H+ exchange and mean blood pressure. V-max and Hill's coefficien t for Na+-H+ exchange were correlated only with mean blood pressure. C onclusions: The demonstration of functional correlations between the k inetic properties of Na+-H+ and Na+-Li+ exchange provides further evid ence that erythrocyte Na+-Li+ exchange is a functioning mode of Na+-H exchange, which is affected by insulin resistance.