Studies on the lithium transport across the red cell membrane

Abstract

Extracellular potassium, bicarbonate, ouabain, dipyridamole and the Na⁺ distribution between red cells and plasma influence Li⁺ transport across the human red cell membrane. The significance of these parameters for theintraindividual variability of the steady-state ratio of external to internal Li⁺ was studied in vitro. Elevation of external K⁺ in the physiological concentration rangeincreases the steady-state distribution ratio Li _e ^/+ /Li _i ^/+ indirectly by increasing the ratio Na _e ^/+ /Na _i ^/+ through activation of the Na⁺−K⁺ pump, and directly by inhibiting ouabain-sensitive Li⁺ uptake. A rise in bicarbonate concentrationdecreases the Li⁺ ratio directly by accelerating Li⁺ uptake through a leak, and indirectly by increasing the Na⁺ leak, thus reducing the Na⁺ ratio. Dipyridamole blocks both bicarbonate effects. Ouabain decreases the Na⁺ ratio and inhibits Li⁺ uptake by the Na⁺−K⁺ pump, thereby exerting two opposite effects on the Li⁺ distribution ratio. The results confirm the previous observation that the steady-state Li⁺ distribution depends strongly on the Na⁺ distribution ratio, i.e., the driving force for Na⁺-dependent Li⁺ uphill countertransport. It is concluded that the Na⁺ distribution between red cells and plasma and the concentrations of K⁺ and bicarbonate in plasma need to be considered as factors influencing the in vivo Li⁺ distribution. However, the considerableinterindividual differences of Li⁺ distribution cannot be ascribed to variations in these parameters.