Accumulation of calcium in the antennal gland during the molting cycle of the freshwater crayfish Procambarus clarkii

Calcium (Ca⁺²) was histochemically localized in antennal glands during the molting cycle of the crayfish Procambarus clarkii. In tissues involved in electrolyte reabsorption, alizarin red S formed precipitates with Ca⁺² (4-30 μm in diameter). In the coelomosac, the number of Ca⁺²-alizarin precipitates did not vary significantly during the molting cycle. In labyrinth and nephridial canal tissues, Ca⁺² precipitates were significantly more abundant during postmolt than during intermolt, with a maximum at 4 days postmolt; by 14 days postmolt, Ca⁺² precipitation had decreased in the labyrinth and nephridial canal, although the values remained significantly greater than intermolt levels. Distal nephridial canal cells treated with potassium oxalate contained mitochondria with electron-dense precipitates (30-85 nm in diameter). These deposits reached a maximum at 4 days postmolt, but remained significantly above intermolt levels by 14 days postmolt. These findings suggest that Ca⁺² accumulates in reabsorptive tissues during postmolt and that the mitochondria of distal nephridial canal cells may also serve to maintain intracellular and extracellular Ca⁺² homeostasis. Additional key words: nephridial canal, labyrinth, alizarin red S, K+-oxalate, histochemistry.