Sodium Regulation in the Crayfish Astacus Fluviatilis

Abstract

1. In Bristol tap water containing 0.4 mM./l. sodium and artificial tap water containing 2 mM./l. sodium, Astacus maintains a blood sodium concentration of about 203 mM./l. This value was not markedly affected by starvation periods of up to a month. 2. Methods of taking small blood and urine samples from individual crayfish at intervals over several hundred hours have been described. 3. Under steady state conditions, curves for the uptake and loss of 22Na by the blood are described by equations derived for a one-compartment system. 4. The volume of this single compartment, which exchanges sodium with the medium, is larger than the actual blood volume by an amount roughly equivalent to the sodium in the tissues. Exchange of sodium between the blood and tissues is probably very rapid. 5. Sodium losses in the urine account for about 6% of the total sodium outflux found using 22Na. The urine sodium concentration of about 6 mM./l. was temporarily increased by conditions such as heavy feeding when the blood may have gained additional sodium. 6. Potential difference measurements across the body surface indicate that the high blood sodium concentration is maintained by active uptake of sodium.