Sodium-lithium countertransport, sodium-hydrogen exchange and membrane microviscosity in patients with hyperlipidaemia.

1. We measured sodium-lithium countertransport, sodium-hydrogen exchange and membrane micro-viscosity in 48 individuals with familial hypercholesterolaemia, 33 subjects with hypertriglyceridaemia and 54 normolipaemic controls. Full lipid profile, blood pressure, body mass index, fasting glucose and insulin levels were also measured. 2. Subjects with hypertriglyceridaemia had higher blood pressure, body mass index, fasting glucose and insulin levels than normal controls. 3. Vmax of the sodium-lithium countertransport was elevated in the hypertriglyceridaemic group compared with controls. Across the whole group log(e) triacylglycerols correlated with Vmax of the sodium-lithium countertransport. There was no difference in sodium-lithium countertransport K(m) between the groups. 4. Sodium-hydrogen maximal proton efflux rate (Vmax) and K(m) were not different between the three groups. There were no correlations between sodium-hydrogen exchange and sodium-lithium countertransport parameters. 5. Microviscosity as measured by diphenylhexatriene was reduced at the core of the membrane in subjects with hypertriglyceridaemia compared with those with familial hypercholesterolaemia or normolipaemic controls, suggesting an alteration in membrane structure. 6. Changes in sodium transport in hyperlipidaemia may be mediated by changes in membrane structure resulting in altered protein conformation or turnover.