Roles of NCX and PMCA in Basolateral Calcium Export Associated with Mineralization Cycles and Cold Acclimation in Crayfish

Basolateral Na + /Ca 2+ exchanger (NCX) and plasma membrane Ca 2+ ATPase (PMCA) are the primary transmembrane proteins that export calcium (Ca 2+ ) from cells. In our lab we use a nonmammalian animal model, the freshwater crayfish, to study cellular Ca 2+ regulation. Two experimental conditions are employed to effect Ca 2+ dyshomeostasis: (a) in the postmolt stage of the crustacean molting cycle increased unidirectional Ca 2+ influx associated with cuticular mineralization is accompanied by elevated basolateral Ca 2+ export (compared with intermolt Ca balance); and (h) exposure of the poikilothermic crayfish to cold acclimation (4°C) causes influx of Ca 2+ into cells, which is compensated by increased basolateral Ca 2+ export (compared with exposure to 23°C). This study compares expression of both NCX and PMCA mRNA (real-time PCR) and protein (Western) in both epithelial (kidney) and nonepithelial tissue (tail muscle) during elevated basolateral Ca 2+ export. Both experimental treatments produced increases in NCX and PMCA expression (mRNA and protein) in both tissues. Mineralization produced greater upregulation of mRNA in kidney than in tail, whereas cold acclimation yielded comparable increases in both tissues. Protein expression patterns were generally confirmatory of real-time PCR data although expression changes were less pronounced. Both experimental treatments appear to increase basolateral Ca 2+ export.