Lithium's inhibition of erythrocyte cation countertransport involves a slow process in the erythrocyte

Summary

Chronic administration of lithium (Li⁺) to human subjects results in reduction of Li⁺/Na⁺ countertransport in their erythrocytes (RBC). The time course of development of inhibition is much slower than one would expect for an immediate effect of Li⁺ on the RBC membrane. Possible explanations include pharmacokinetic delays, a mediating humoral agent, and a slow process in the RBC. To discriminate among these possibilities, we incubated human RBC in sterile culture by the method of Freedman (Freedman, J. C. 1983J. Membrane Biol. 75:225–231), which permits much longer incubations than other methods.

As gauged by eight measures, the incubated RBC remain viable for two weeks. Small changes in intracellular concentrations with time during incubation are in the same direction as the changes associated with natural aging of RBCin vivo, except for a rise in ATP and related cation shifts during the first few days of incubation. Treatment of incubated RBC with 2mm Li⁺ inhibits countertransport by 48% without affecting Li⁺ leak efflux. The inhibition develops slowly: it is half-maximal after 1–2 days and maximal by 4–7 days. Differences betweenin vivo results and our incubated cells in the time course of inhibition are as expected from the pharmacokinetic delays operatingin vivo. The inhibition is reversible on removing Li⁺. Li⁺ inhibits countertransport similarly slowly and to a similar degree from inside the RBC and from outside.

Hence the slow time course of inhibitionin vivo is not due to a humoral factor or to the time required for intracellular Li⁺ accumulation and is only partly due to pharmacokinetic delays. The delay must involve an unidentified slow process at the level of the RBC.