Concentration of sodium and free amino acids in the haemolymph and other fluid compartments in an adephagous and a polyphagous species of beetle

1. 1. The extracellular and intracellular concentrations of sodium and free amino acids were determined in the adephagous beetle Carabus nemoralis and the polyphagous beetle Rhagium inquisitor acclimated to 0 and 25°C. 2. 2. C. nemoralis had substantially higher extracellular sodium concentrations than R. inquisitor, and also substantially lower extracellular concentrations of free amino acids. 3. 3. The possible mechanistic relationship between the transmembrane sodium distribution and the distribution of free amino acids via symport mechanisms is discussed.