Secretory granule-cytoplasm relationships in serous glands of anurans: ultrastructural evidence and possible functional role

A survey covering the serous (granular) cutaneous glands in several anuran families from the Old and New Worlds (Bombinatoridae, Discoglossidae, Ranid ae, Hylidae, Pseudidae and Leptodactylidae) has revealed consistent pattern s of complex interactions between the syncytial secretory unit and serous d eposits (granules). These relationships involve outgrowths from the syncyti al cytoplasm encircling the granules and complex invaginations of the perig ranular compartment (halo) into the syncytium. The outgrowths are branched, cytoplasm processes resembling ramified microvilli, or can be larger, dome -like to cylindrical structures. Despite their different features and origi ns, all these structures are efficient devices for amplifying the cytoplasm ic surfaces round the granules, so improving exchange between the secretory syncytium and serous product. These complex secretory granule-cytoplasm in teractions affect the product released from the Golgi apparatus and are con sistent with the hypothesis of prolonged serous maturation Following the in itial phase of biosynthesis. Post-Golgian maturation modifies the secretory material on a centripetal gradient, causing condensation and, possibly, th e transfer of component molecules from and/or to the cytoplasm. (C) 2001 El sevier Science Ltd. All rights reserved.