Calcium transport in crayfish gastrolith disc: Morphology of gastrolith disc and ultrahistochemical demonstration of calcium

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Abstract
After induction of premolt conditions in crayfish by injection of the molting hormone (β‐ecdysone), gastrolith disc tissue was examined electron‐microscopically. The following four types of epithelial cells were morphologically distinguished, synchronized with the stage of gastrolith growth. Type 1 cells, containing abundant mitochondria with microtubules extending from apical to basal side, are abundant during the intermolt period. Type 2 cells, highly vacuolated and containing hypertrophied mitochondria, are involuting and abundant during the period of gastrolith formation. Type 3 cells, having fine microvilli at the apical portion, begin to appear at the large gastrolith period. Type 4 cells, containing many irregular vesicles at the apical portion with mitochondria present in basal infoldings, are seen when the gastrolith formation is completed.These observations led to the assumption that the four types of cells represent the whole life cycle of an epithelial cell, starting from type 3 through type 4, type 1, and ending at type 2 involuting cells.From ultrahistochemical demonstration of calcium, the presence of calcium was nearly restricted to the hypertrophied mitochondria of type 2 cells, which eventually slough off to the gastric lumen.These findings suggest a unique calcium transport system: The hypertrophied mitochondria accumulate a large amount of calcium and supply calcium to the gastrolith.

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