The total extracellular proteins and the most abundant 960 intracellular proteins of clonal CNS nerve and glial cell lines were examined by quantitative 2-dimensional acrylamide gel electrophoresis. While less than 0.2% of the intracellular proteins differ among the 5 nerve and 4 glial cell lines studied, over 65% of the extracellular proteins vary in distribution between the 2 major classes of CNS cells. These data indicate that the phenotypic complexity of nerve and glia populations is similar and that most of the protein complexity is in extracellular molecules.It has been argued on the basis of RNA hybridization studies that the mammalian CNS has a severalfold higher number of unique mRNA sequences than other tissues (Brown and Church, 1972;Chikaraishi et al., 1983; Hahn and Laird, 197 1). Assuming that these mRNAs are translated, there are 2 alternatives that could explain the apparent increase in protein complexity within the brain; they are not mutually exclusive. Each cell within the CNS might make many more species of proteins than cells of other tissues, or there might be a greater number of cell types, each making a few unique species that contribute to total tissue complexity but whose overall protein complexity is similar to cells of different tissues. To distinguish between these alternatives, protein synthesis in a series of clonal CNS nerve and glial cell lines was examined by 2-dimensional gel electrophoresis. Total cellular protein synthesis and the extracellular proteins released into the culture medium were analyzed by computer-assisted methods. It is shown that there is a great deal of variability in the protein species synthesized by cells from the rat CNS and that the variability within the glial population is as great as that between the nerve cells. The majority of this protein complexity is associated with the extracellular proteins, which are more abundant in nerve and glia than in mesodermally derived cells. The total number of cellular proteins synthesized by clonal CNS cell lines is, however, indistinguishable from that of mesodermal cells. It follows that the higher protein complexity in the CNS is due to both the large number of unique phenotypes and the increased number of extracellular proteins relative to other tissues. Materials and MethodsCell lines

Inhibition of DNA polymerase g by nucleoside reverse transcriptase inhibitors (NRTIs) can cause mitochondrial dysfunction and cellular toxicity. Hyperlactataemia, which is a consequence of a shift in the metabolism of pyruvate, is an indicator of nucleoside-related mitochondrial toxicity. MethodsWe evaluated exercise and oxidative capacities as well as circulatory and ventilatory responses to exercise in 24 HIV-infected patients on NRTIs presenting hyperlactataemia [mean (AE standard deviation) fasted lactate 5 3.5 AE 1.1 mmol/L]; 27 NRTI-treated patients with normal baseline lactate concentrations were used as controls (mean fasted lactate 5 1.6 AE 0.3 mmol/L). ResultsIn the patients with hyperlactataemia, the average peak work capacity (1.7 AE 0.6 W/kg) and peak oxygen consumption (VO 2 ) (21 AE 4 mL/kg/min) were significantly lower (Po0.01) than in control subjects (work, 2.1 AE 0.4 W/kg; VO 2 , 25 AE 4 mL/kg/min). The capacity to increase oxygen extraction during exercise was significantly diminished in the hyperlactataemia group, as shown by a low peak systemic arteriovenous oxygen difference (a-vO 2 ) difference compared with controls (11 AE 3 vs 14 AE 3 mL/dL; P 5 0.008), and as indicated by a linear correlation between VO 2 and systemic a-vO 2 difference (r 2 5 0.76). During exercise, the increases in cardiac output relative to VO 2 (mean D cardiac output (Q)/DVO 2 5 8 AE 3.6) and ventilation (mean D ventilation (VE)/DVO 2 5 48.6 AE 13.2) were significantly higher in hyperlactataemia patients compared with controls (mean cardiac output D(Q)/DVO 2 5 6 AE 2; mean DVE/DVO 2 5 42 AE 12.7; P 5 0.03). ConclusionsThe degree of exercise limitation in patients with nucleoside-related mitochondrial toxicity correlates directly with the severity of impaired muscle oxidative phosphorylation, as indicated by the capacity for muscle oxygen extraction. Exaggerated circulatory and ventilatory responses to exercise are direct consequences of the level of impaired muscle oxidative phosphorylation.