Receptor-mediated calcium influx in Chlamydomonas reinhardtii

Alcian blue acts as a secretagogue and chemorepellent in a variety of unicellular eukaryotes. We report that alcian blue stimulates flagellar excision and induction of RNA encoding flagellar proteins in Chlamydomonas reinhardtii. Flagellar excision by alcian blue is dependent on extracellular Ca2+ and is blocked by La3+, ruthenium red, and neomycin, and so is similar to flagellar excision by acid shock. However, the adf-1 mutant excises its flagella following alcian blue treatment, but not following acid shock, thus genetically distinguishing alcian-blue-induced excision from acid-shock-induced excision. Wild-type, but not adf-1, cells regrow their flagella in the continued presence of alcian blue. Wild-type cells that regrow flagella in the presence of alcian blue fail to excise their flagella in response to either increased concentrations of alcian blue or to acid shock. Alcian blue treatment of cells also induces RNA encoding flagellar components, but in a manner distinct from other means of stimulation. These results suggest that treating Chlamydomonas with the secretagogue alcian blue initiates it Ca2+ influx pathway and that prolonged treatment with alcian blue desensitizes the acid-shock-activated Ca2+ influx pathway to acid treatment. Alcian blue will thus be a useful excitatory ligand in future studies of receptor-mediated Ca2+ signaling in the Chlamydomonas flagellar regeneration system.