INTRACELLULAR CALCIUM IN THE CELLS OF THE OUTER MANTLE EPITHELIUM OF ANODONTA-CYGNEA

1. The intracellular concentration of ionized calcium was measured with double-barrelled ion-sensitive microelectrodes under short-circuit conditions in the isolated outer mantle epithelium of Anodonta cygnea. 2. When the outside baths contained 1 mmol/l Ca2+ the average intracellular Ca2+ was 5.42 +/- 0.64 mmol/l (N = 41) while the equilibrium concentration estimated from the intracellular potential measured in the same cells was 5.51 +/- 0.33 mmol/l. 3. Bilateral removal of calcium from the external baths induced a fast fall in the intracellular concentration of this ion by almost three orders of magnitude. This effect was similar to that obtained by removing calcium from the bath on the basolateral side. 4. Removal of calcium from the bath in contact with the apical side of the preparation had little effect on intracellular calcium.