Septate and gap junctions between the epithelial cells of an invertebrate, the mollusc Cominella maculosa

Abstract

In most investigations of invertebrate epithelial cells only septate junctions have been identified. The present study has shown that a junctional complex involving both septate and gap junctions is present between the epithelial cells of Cominella maculosa, a stenoglossan prosobranch (Mollusca). As gap junctions fulfill the communicating function between epithelial cells in vertebrate junctional complexes, they have been interpreted as fulfilling this role in the invertebrate studied during the present investigation. This has allowed the septate junctions to be interpreted as having only a sealing function. Freeze-etch replicas of septate junctions indicate that regular rows of particles occur within both plasma membranes in the junctional region. Evidence is presented which suggests that these particles are located within ridges on the external surface of each plasma membrane. Complementary ridges on the two membranes would then give the sealing function of the junction.