Cellular uptake of lithium via amino acid transport system A.

We now add to the agencies by which cells take up lithium the process of cotransport with neutral amino acids via System A. In the Ehrlich cell various natural and synthetic amino acids, depending on their structure, can cause substantial accelerations of Li+ uptake over a considerable range of levels of Na+, Li+ and H+. Half the maximal augmentation of uptake, namely 1.2 mequiv. Li/kg cell water per 15 min, was obtained for 5.4 mM alanine in a double-reciprocal plot. Alanine also stimulated the exodus of Li+ from the Ehrlich cell. The human red blood cell, lacking System A as it does, becomes an imperfect model for studying cellular uptake of Li+. Until the Li+ dependence of amino acid uptake in the reticulocyte is known, reticulocytosis can be suspected of contributing to the interpersonal variations seen in Li+-for-Na+ exchange.