Cell glutamate-damage induced by overstimulation of ionotropic receptors is initiated by modification of the intracellular Ca 2+ homeostasis and the concomitant activation of Ca 2+ -dependent cysteine proteases, the calpain and caspase families. The resultant cleavage of target molecules mediates a critical function in the execution of the cell death. In this work, we investigated relationships between the activity of calpain and glutamate-or kainate-induced apoptosis in several organs of Xenopus laevis tadpole. Animals (stage 48) were incubated for 3 hours with glutamate (30-120 mM) or kainate (0.015-0.75 mM) and the rise of both apoptosis and calpain was observed in several organs. Our results indicated that glutamate (120 mM) or kainate (0.15 mM) exposure induced cell death with apoptotic features. The toxic effects of drugs into the organs were variable. Apoptosis was probably not the only form of cell death and option of necrosis or apoptosis was depending on the stimulation degree of the receptor, i.e. the receptor type, intensity and time course of molecule exposure. The increase of ubiquitous calpain was not correlated with the peak of apoptosis, suggesting the role of calpain in cell death was complex: calpain and caspase pathways were tightly interrelated in the glutamate-or kainate-induced cell death and the contribution of calpain to another type of death than apoptosis was perhaps preferred.
Calpains are a superfamily of Ca 2+ -dependent cysteine proteases, implicated in various cellular processes and thus probably necessary in all the stages of cell life. The first extended report of quantification of total RNAs within the developmental stages of Xenopus laevis was described in this study. Decreases of total RNAs were positively associated with waves of apoptotic cell death (onset of gastrulation, and morphogenesis). Using qPCR, the temporal expression pattern of CAPN1 and CPAN8b (XCL-2) were characterized during the Xenopus laevis embryogenesis. Transcripts of the CAPN1 and CAPN8 genes were detectable from gastrula stage and their levels oscillated throughout development. The expression of the CAPN1 (mu/I) gene was observed in earliest stage, indicating a maternal origin, while expression of the CAPN8b gene was detectable after midblastula transition. The levels of the two transcripts then started to rise again obviously as a result of zygotic expression (stage 11). The CAPN1 gene expression was particularly expressed at tailbud stage, while the CAPN8 transcripts were found at gastrula, neurula and tailbud stages. This is the first report of quantification of mRNAs CAPN8b and CAPN1 (mu/I) within the developmental stages of Xenopus laevis by qPCR.
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