The relationship between [Ca2+]i and cell death using an in vivo model: a study using the ced-1 mutant strain of C. elegans.

The ced-1 mutant of the free-living nematode, Caenorhabitis elegans, was used to study cell injury and cell death in relation to changes in intracellular ionized calcium ([Ca2+]i). This animal, which is being genetically characterized, may prove to be extremely useful for certain toxicologic studies because of its small size, optical transparency, rapid generation time, and the morphologic and genetic data currently available. During the development of this animal, 131 of 1,090 ultimate somatic cells undergo programmed cell death. Using mutagenesis techniques, several genes responsible for this death have been identified. In this study, we have taken advantage of the ced-1 mutant in which dead cells accumulate, as they cannot be phagocytized and removed. Although changes in [Ca2+]i have been studied in relation to cell injury and cell death, observations have been essentially restricted to in vitro monolayer cultures because of the methodology involved. To study the relationship between changes in [Ca2+]i and injury in vivo, we selected this animal model for further study and report here the morphological changes following the effects of ionomycin treatment in relation to increases of [Ca2+]i and cell death as measured using the fluorescent probes Fluo-3/AM and propidium iodide, respectively. The technique of confocal laser scanning microscopy is ideally adapted to such measurements in these living animals, and the results can be readily correlated with those made with Nomarski differential interference contrast microscopy as well as with transmission electron microscopy. The results support previous in vitro observations and show that early increases of [Ca2+]i accompany early reactions to injury. Furthermore, the results also show that changes in this small invertebrate metazoan parallel those seen in mammalian systems, including human. Thus, the current study indicates that ced-1 C. elegans can potentially serve as an in vivo model not only for evaluating the possible temporal relationship of [Ca2+]i elevation with cell death but also for evaluating the [Ca2+]i elevation observed in relation to other phenomena and in evaluating toxic agents.