Optical imaging of calcium transients in neurons and pharyngeal muscle of C-elegans

Electrophysiology and optical indicators have been used in vertebrate syste ms to investigate excitable cell firing and calcium transients, but both te chniques have been difficult to apply in organisms with powerful reverse ge netics. To overcome this limitation, we expressed cameleon proteins, geneti cally encoded calcium indicators, in the pharyngeal muscle of the nematode worm Caenorhabditis elegans. In intact transgenic animals expressing camele ons, fluorescence ratio changes accompanied muscular contraction, verifying detection of calcium transients. By comparing the magnitude and duration o f calcium influx in wild-type and mutant animals, we were able to determine the effects of calcium channel proteins on pharyngeal calcium transients. We also successfully used cameleons to detect electrically evoked calcium t ransients in individual C. elegans neurons. This technique therefore should have broad applications in analyzing the regulation of excitable cell acti vity in genetically tractable organisms.