Abstract
ABSTRACT Calcium regulation in normal and calcium-depleted snails has been investigated. L. stagnalis has an uptake mechanism with a high affinity for calcium ions and shows a positive calcium balance in media containing more than 0·062 mM Ca/l. Influx and net uptake of calcium are related to external calcium concentration in a non-linear manner. The uptake mechanism is half-saturated and near-saturated in external media containing 0·3 and 1·0–1·5 mM Ca/l respectively. Calcium uptake from external concentrations of less than 0·5 mM Ca/l is against a small electrochemical gradient whereas from external concentrations greater than 0·5 mM Ca/l there is no adverse gradient. Calcium depletion does not significantly alter the normal influx or net uptake rate of calcium from 1·o mM Ca/l. The calcium concentration in the blood remains constant during net uptake from, and net loss to, the medium. A comparison is made between the mechanisms of sodium regulation and calcium regulation in L. stagnalis.
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