KIEHN, L.*; SALEUDDIN, A.S.M.; MUKAI, S.T.; York University, Toronto, Ontario; York University, Toronto, Ontario; York University, Toronto, Ontario: The Role of Calcium in Protein Secretion in the Albumen Gland of Helisoma duryi (Mollusca)

The albumen gland of the freshwater pulmonate snail Helisoma duryi produces and secretes the perivitelline fluid, which coats fertilized eggs and provides nutrients to the developing embryos. It is known that the perivitelline fluid secretion is stimulated by dopamine and forskolin and that Gi and Gs proteins, adenylate cyclase and protein kinase A are involved. This paper provides evidence of the role of calcium, phospholipase C, IP₃ and protein kinase C in perivitelline fluid secretion by the albumen gland based on protein secretion experiments and IP₃ assays. Both extracellular and intracellular calcium plays a role in the signaling process of protein secretion by the albumen gland. Cyclic AMP, synthesized by receptor coupled adenylate cyclase, activates protein kinase A, which presumably phosphorylates L-type calcium channels on the plasma membrane leading to an increase in cytosolic calcium concentration, which is a prerequisite for the stimulation of perivitelline fluid exocytosis. Phospholipase C appears not to be involved in regulating protein secretion and, consequently, IP₃, diacylglycerol and protein kinase C are not involved either. Intracellular calcium stores seem to play a role in the signaling, possibly through other types of calcium channels and other signaling pathways since neither IP₃ receptors nor ryanodine receptors were implicated. Combining the data in this paper with the results from our earlier studies, a model for signaling of perivitelline fluid release from the albumen gland secretory cells is proposed.