A calfluxin-related peptide is present in the bag cells and atrial gland of Aplysia

The caudodorsal cells of Lymnaea and the bag cells of Aplysia are neuroendocrine cells whose peptide products have homologous functions, i.e., regulation of egg deposition. One of the Lymnaea products, calfluxin, increases cytosolic and hence mitochondrial calcium concentrations in secretory cells of the albumen gland, an exocrine organ that secretes perivitellin fluid around the egg cells during packaging; the changes can be visualized at the ultrastructural level for quantification with the pyroantimonate precipitation technique and are correlated with changes in the secretory and biosynthetic activity in the gland. Comparable studies have now been carried out with Aplysia and indicate that the bag cells of A. californica and A. brasiliana also contain a factor with calfluxin-related activity, and that the factor is not the egg-laying hormone (ELH). The bag cell factor does not affect mitochondrial calcium levels in the Lymnaea albumen gland, and synthetic calfluxin does not affect the Aplysia gland. Thus, although the bag cell and caudodorsal cell peptides have the same activity in their respective genera, the sequences have diverged sufficiently during the course of evolution to preclude cross-reactivity. Calfluxin-related activity was also detected in the atrial gland of A. californica and the atrial gland-like epithelium of A. brasiliana, two exocrine organs in the oviduct that express genes structurally related to the bag cell ELH gene. It is postulated that the active atrial gland factors may be peptides A and B.