A mechanism for the accumulation of choline in erythrocytes during treatment with lithium

We have examined the kinetics of isotopic exchange of choline (Ch) between erythrocytes and the medium in which they are suspended during a 4 hr incubation at 37 ° C using [²H₄]-Ch in the medium at a concentration (10 μM) similar to that in plasma. [²H₀]- and [²H₄]-Ch in erythrocytes and medium were measured by gas chromatography mass spectrometry (GCMS). A steady state was experimentally verified. The kinetics of exchange closely obeyed a simple model from which is was possible to estimate influx and efflux of Ch in three normal human subjects. In all subjects there was a substantial net efflux of Ch (78, 355 and 335 pmol m1^-1min^-1) which represents Ch released from phospholipids within the cells. We propose that the rise in erythrocyte Ch levels during treatment with lithium is due to the inability of Ch to escape as fast as it is released when the transport system is inhibited by lithium.