DYNAMICS OF CALCIUM REGULATION IN PARAMECIUM AND POSSIBLE MORPHOGENETIC IMPLICATION

This paper is the first report of the use of a fluorescent indicator ( Dextran-coupled calcium green-1) for imaging of cytosolic free calcium in ciliate cells. Using this technique in Paramecium, we show that a very transient increase in the mean intracellular calcium concentratio n accompanied exocytosis. It has long been postulated based on indirec t experimental evidence, that a calcium wave which would spread across the cortex at the time of cell division, would be the primary event t hat triggers morphogenesis in these species. We theoretically show tha t a unifying interpretation can be given for the possible occurrence o f a single wave and that of multiple oscillations of cytosolic calcium : both of which correspond to two different behaviors of the same dyna mic system. Experimental conditions allowing the visualization of poss ible calcium periodicities in the interphase Paramecium cell are much more easily fulfilled than those permitting the observation of a singl e wave at the time of cell division. Hence, experiments were performed on interphase cells. After microinjection of calcium indicator into a mutant strain which is defective in exocytosis, we observed Ca2+ osci llations with a period close to 2 minutes. Hence, we conclude that Par amecium possesses all the dynamic elements required to generate, at th e time of cell division, a morphogenetic calcium wave.