Pharynx mitochondrial [Ca2+] dynamics in live <i>C. elegans</i> worms during aging

Abstract

Progressive decline in mitochondrial function is generally considered one of the hallmarks of aging. We have expressed a Ca²⁺ sensor in the mitochondrial matrix of <i>C. elegans</i> pharynx cells and we have measured for the first time mitochondrial [Ca²⁺] ([Ca²⁺]_M) dynamics in the pharynx of live <i>C. elegans</i> worms during aging. Our results show that worms stimulated with serotonin display a pharynx [Ca²⁺]_M oscillatory kinetics that includes both high frequency oscillations (up to about 1Hz) and very prolonged "square-wave" [Ca²⁺]_M increases, indicative of energy depletion of the pharynx cells. Mitochondrial [Ca²⁺] is therefore able to follow "beat-to-beat" the fast oscillations of cytosolic [Ca²⁺]. The fast [Ca²⁺]_M oscillations kept steady frequency values during the whole worm life, from 2 to 12 days old, but the height and width of the peaks was progressively reduced. [Ca²⁺]_M oscillations were also present with similar kinetics in respiratory chain complex I <i>nuo-6</i> mutant worms, although with smaller height and frequency than in the controls, and larger width. In summary, Ca²⁺ fluxes in and out of the mitochondria are relatively well preserved during the <i>C. elegans</i> life, but there is a clear progressive decrease in their magnitude during aging. Moreover, mitochondrial Ca²⁺ fluxes were smaller in <i>nuo-6</i> mutants with respect to the controls at every age and decreased similarly during aging.