METABOLIC HEAT DISSIPATION AND INTERNAL SOLUTE LEVELS OF ARTEMIA EMBRYOS DURING CHANGES IN CELL-ASSOCIATED WATER

Embryos (cysts) of the brine shrimp Anemia enter a profound, yet reversible, state of metabolic arrest in response to cellular dehydration. We have monitored metabolic activity during this transition in embryos from the Great Salt Lake population by using microcalorimetric measurements of heat dissipation. Embryo hydration states can be precisely controlled by immersing cysts in solutions of varying ionic strength. When developing embryos were incubated in a 2-0moll"1 NaCl solution, heat dissipation fell after 20 h to l-OmWg " 1 dry mass, or 21 % of the value obtained when embryos were in control solutions of 0-25moll"1. At higher ionic concentrations, heat dissipation declined to as low as 3 % of control values. Recovery from dehydration was rapid. Energy flow increased to 135 % of control values within 2h after returning cysts to the control medium. These metabolic transitions were correlated with embryo hydration levels measured across the same dehydration series. Total cyst water ranged from 112 ±2-6gH20100 g"1 dry mass in 0-25 moll"1 NaCl to 46±0-6gH2O100g"1 dry mass in 5-0 moll"1 NaCl. At the first point where heat dissipation wa