Meeting Abstract

25.6  Friday, Jan. 4  Metabotropic Glutamate Signalling System in a Freshwater Sponge ELLIOTT, GRD*; LEYS, SP; University of Alberta; University of Alberta gelliott@ualberta.ca

Ephydatia muelleri propagates contractions across the sponge body to expel waste or stagnant water. The entire behaviour consists of a peristaltic contraction of the incurrent canals that progresses to the excurrent canals, eventually moving water towards and out of the osculum. We hypothesize that a chemical messenger working in a paracrine manner controls the progression of the contraction through the choanosome in a calcium dependent manner. Since there is no evidence that sponges possess either voltage or ligand gated ion channels such as those found in neurons, we tested whether a metabotropic glutamate signalling system coordinates the slow contractions. We found that L-glutamate, an ubiquitous and ancient signalling molecule, triggers contractions in a dose-dependent manner with stimulation of the full inflation-contraction event at a threshold concentration of 75-80 uM. Lower concentrations generated smaller or no contractions, and higher concentrations caused seizure of all the canals, destroying the sponge. Contractions are reduced by the prior incubation in the general metabotropic glutamate blocker AP3 and/or calcium-free media buffered with EDTA, EGTA and BAPTA, indicating external calcium is required for propagated events.