Meeting Abstract

32.1  Monday, Jan. 5  Evidence for chemical signalling systems (Glutamate, GABA and Nitric Oxide) involved in coordinated body contractions of Ephydatia muelleri. ELLIOTT, Glen RD*; LEYS, Sally P; University of Alberta gelliott@ualberta.ca

Sponges are benthic suspension feeders that are considered to lack a tissue level of organization, sensory cells and coordinated behaviour. Recent molecular and physiological studies suggest that the Porifera have cell signalling systems similar to those found in higher metazoans. Unfortunately, few model systems exist in the Porifera that enable functional experiments to be undertaken to examine their physiology. The demonstration of coordinated contractions of canals that function to expel waste water in Ephydatia muelleri prompted us to examine the physiology of these contractile canals. It is hypothesized that sponges are able to coordinate or modulate contractions by the use amino acids (Glutamate or GABA) or short-lived gases (Nitric Oxide). Using a combination of digital time-lapse microscopy, HPLC, immunocytochemistry, and pharmacological manipulations provides a description of signalling systems in the freshwater sponge. HPLC analysis of sponge tissue for free amino acids identified pools of glutamate, glutamine, and GABA used to maintain a metabotropic receptor signalling system. Application of glutamate induces contractions in a dose dependent manner and application of GABA induces rapid twitches of the choanosome. Nitric oxide induces the contraction of the osculum and nitric oxide synthase has been localized in mesenchyme cells of the apical pinacoderm, choanocytes and in cells surrounding excurrent canals and osculum, which is corroborated by using a cGMP assay indicating that the Nitric oxide system is functional. We propose that Ephydatia muelleri has chemical signalling systems to coordinate (Glutamate, GABA) or to locally modulate contractions (Nitric oxide).