Biochemical studies of phenylalanine ammonia-lyase encapsulated in erythrocytes.

37°C. Krebs-Henseleit bicarbonate buffer solutions were added to the hemichambers on each side of the tissue: the buffer on the mucosal (lumen) side was modified such that lithium chloride replaced sodium chloride at concentrations ranging from 0 to 40 mmol/l. The extracellular marker polyethylene glycol, M, 900 (PEG-900), was also present in buffer solutions on the mucosal side of the tissue. Subsequently, the effects of the combined metabolic inhibitors 2,4dinitrophenol (DNP) and NaF, on tissue uptake of lithium were investigated. At the conclusion of the experiments blood for serum lithium assay was obtained by cardiac puncture; these and all other lithium estimations were performed using atomic absorption spectrometry. Mean serum lithium was 2.1 1 (s.E.M. 0.24) mmol/l, well into the accepted toxic range for man; however, despite some weight loss, the animals did not appear to be ill or otherwise distressed. Lithium was detected to a mean concentration of 1.16 (s.E.M. 0.06) nmol/ mg wet weight in intestinal epithelial mucosa removed from animals before further lithium exposure in vitro. This contrasts with negligible tissue uptake of lithium under conditions of acute exposure in vitro [6], and reflects accumulation of lithium in the enterocytes during the 2 1-day treatment period. Tissue lithium was calculated after exposure to mucosal buffers containing lithium at concentrations ranging from 0 to 40 mmol/l. Allowance was made for lithium associated with the extracellular space, calculated from tissue retention of the extracellular marker PEG-900. After incubation in mucosal buffer containing 0 and 5.0 mmol of lithium/l tissue lithium had fallen to values which were less than the mean concentration before incubation of the tissue [0.41 (s.E.M. 0.05) nmol/mg and 0.73 (s.E.M. 0.14) nmol/mg, respectively]. Thus, at these low external concentrations of lithium net efflux was observed. In contrast, at concentrations of 20 and 40 mmol of lithium/l in the mucosal buffer net tissue uptake was observed [2.97 (s.E.M. 0.47) nmol/mg and 4.97 (s.E.M. 0.44) nmol/mg, respectively]. In the presence of DNP (0.5 mmol/l) and NaF (5.0 mmol/l) tissue uptake of 20 mmol of lithium/l in the mucosal buffer was prevented. There was no significant difference between tissue lithium concentrations in the presence of both 20 mmol of lithium/l and the combined metabolic inhibitors [ 1.20 (s.E.M. 0.3 1) nmol/mg, n = 81 and the lithium concentration in freshly removed tissue [ 1.16 (s.E.M. 0.06) nmol/mg, n = 91. A further experiment was performed to investigate the effects of a wider range of inhibitors on tissue uptake of 16 mmol of lithium/l in the mucosal buffer (Table 1). These data confirm a significant reduction in lithium uptake in the Table 1. Effects of specific inhibitors on tissue lithium uptake in guinea-pigs chronically exposed to lithium