Ion relations of haemolymph, palliai fluid, and mucus of Lymnaea stagnalis

Abstract

The concentrations, and where possible, activities of the main inorganic ions were measured in haemolymph, palliai fluid, and mucus of Lymnaea stagnalis appressa Say (Gastropoda: Pulmonata), and in the artificial pond water (APW) in which the snails were stored. Activity coefficients of Na, K, Ca, and Cl in pallial fluid and in APW were compared with values calculated from Debye–Hückel theory. Some Na and Ca in pallial fluid, and Ca in APW are probably bound in organic or inorganic complexes. Comparison of the Nernst potentials with the transepithelial potential difference supports the idea that Na, K, Ca, and Cl must be actively taken up from APW by the snail. Pallial fluid is not identical to haemolymph and is probably a mixture of urine and haemolymph. Pallial fluid contaminates mucus during mucus collection. A method of correcting for this contamination is given. After correction, mucus had higher Ca and K, and possibly higher Mg concentrations than did haemolymph. Mucus had a high concentration of NH4+. Possible sources of ions in mucus are discussed. Mucus secretion rates are low enough that this is not an important cause of ion loss to the snail. Using ether to stimulate mucus secretion alters the water and K content of the mucus.