Objective: To ascertain the relationships between the kinetic properties of erythrocyte Na+-H+ exchange [maximum kinetic energy (Vmax), Michaelis constant (Km) for internal H+ and Hill's coefficient], Na+-Li+ (Vmax and Km for external Na+), and metabolic parameters in normotensive 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) subjects.
Results: In comparison with normotensives, the hypertensives had a higher Vmax for Na+-Li+ and Na+-H+ exchange, a higher Km for external Na+ for Na+-Li+ exchange and a lower reduced Hill's number for Na+-H+ exchange. Vmax values for Na+-Li+ and Na+-H+ exchange were significantly correlated, as were Km values for internal H+ for Na+-H+ exchange and Km for external Na+ for Na+-Li+ exchange. Insulin resistance and beta-cell function indices were higher in the hypertensives than the normotensives. Upon stepwise multiple regression analysis, Vmax for Na+-Li+ exchange was correlated significantly and independently with Km for external Na+ and with the insulin resistance index, while Km for external Na+ was correlated with Km for internal H+, Vmax for Na+-H+ exchange and mean blood pressure. Vmax and Hill's coefficient for Na+-H+ exchange were correlated only with mean blood pressure.
Conclusions: The demonstration of functional correlations between the kinetic properties of Na+-H+ and Na+-Li+ exchange provides further evidence that erythrocyte Na+-Li+ exchange is a functioning mode of Na+-H+ exchange, which is affected by insulin resistance.