Long-term monitoring of Ca(2+) dynamics in C. elegans pharynx: an in vivo energy balance sensor

Ca(2+) is a key signal transducer for muscle contraction. Continuous in vivo monitoring of intracellular Ca(2+)-dynamics in C. elegans pharynx muscle revealed surprisingly complex Ca(2+) patterns. Despite the age-dependent decline of pharynx pumping, we observed unaltered fast Ca(2+) oscillations both in young and old worms. In addition, sporadic prolonged Ca(2+) increases lasting many seconds or minutes were often observed in between periods of fast Ca(2+) oscillations. We attribute them to the inhibition of ATP-dependent Ca(2+)-pumps upon energy depletion. Accordingly, food deprivation largely augmented the frequency of prolonged [Ca(2+)] increases. However, paradoxically, prolonged [Ca(2+)] increases were more frequently observed in young worms than in older ones, and less frequently observed in energy-deficient mitochondrial respiratory chain nuo-6 mutants than in wild-type controls. We hypothesize that young animals are more susceptible to energy depletion due to their faster energy consumption rate, while nuo-6 mutants may keep better the energy balance by slowing energy consumption. Our data therefore suggest that the metabolic state of the pharynx during feeding stimulation depends mainly on the delicate balance between the instant rates of energy production and consumption. Thus, in vivo monitoring of muscle Ca(2+) dynamics can be used as a novel tool to study cellular energy availability.