Arrestment of carbohydrate metabolism during anaerobic dormancy and aerobic acidosis inArtemia embryos: determination of pH-sensitive control points

Summary Changes in concentrations of trehalose, glycogen, glycerol, some glycolytic intermediates and adenylate nucleotides that occur during aerobic development have been compared to those seen during anaerobic dormancy and aerobic acidosis in gastrula-stage embryos ofArtemia. The latter two incubation conditions are known to foster large drops in intracellular pH (Busa et al. 1982; Busa and Crowe 1983).During aerobic development, trehalose levels decline while glycogen and glycerol are synthesized (Fig. 1). These transitions are blocked during both anaerobic dormancy and aerobic acidosis, but are resumed by return of embryos to aerobic incubation (Fig. 1). Thus, it is concluded that carbohydrate catabolism in hydrated embryos is directly modulated by intracellular pH. Changes in metabolite levels (Figs. 2–4) reveal that this process is controlled primarily at the trehalase and hexokinase reactions with a less-pronounced negative crossover point noted at the phosphofructokinase step. Each of these reactions is shown to be nonequilibrium by comparing the mass action ratio to the equilibrium constant (Table 1).When embryos are placed under anaerobic conditions, ATP levels drop dramatically while AMP increases in concentration (Fig. 5). These changes are reflected in a drop in adenylate energy charge from a control value of 0.73 to 0.42 (Fig. 6). Aerobic acidosis only leads to a slight decrease in energy charge, emphasizing that shifts in adenylate poolsAbbreviations pH _i intracellular pH - glyceraldehyde 3-P glyeraldehyde 3-phosphate - DHAP dihydroxyacetone phosphate - glucose 6-P glucose 6-phosphate - fructose 6-P fructose 6-phosphate - fructose 1,6-P ₂ fructose 1,6-bisphosphate - HK hexokinase - PFK phosphofructokinase - MAR mass action ratio - K _eq equilibrium constant