Intestinal Ca2+wave dynamics in freely movingC. eleganscoordinate execution of a rhythmic motor program

Abstract

Defecation in the nematode worm Caenorhabditis elegans is a highly rhythmic behavior that is regulated by a Ca2+wave generated in the 20 epithelial cells of the intestine, in part through activation of the inositol 1,4,5-trisphosphate receptor. Execution of the defecation motor program (DMP) can be modified by external cues such as nutrient availability or mechanical stimulation. To address the likelihood that environmental regulation of the DMP requires integrating distinct cellular and organismal processes, we have developed a method for studying coordinate Ca2+oscillations and defecation behavior in intact, freely behaving animals. We tested this technique by examining how mutations in genes known to alter Ca2+handling [including egl-8/phospholipase C (PLC)-β, kqt-3/KCNQ1, sca-1/sarco(endo)plasmic reticulum Ca2+ATPase, and unc-43/Ca2+-CaMKII] contribute to shaping the Ca2+wave and asked how Ca2+wave dynamics in the mutant backgrounds altered execution of the DMP. Notably, we find that Ca2+waves in the absence of PLCβ initiate ectopically, often traveling in reverse, and fail to trigger a complete DMP. These results suggest that the normal supremacy of the posterior intestinal cells is not obligatory for Ca2+wave occurrence but instead helps to coordinate the DMP. Furthermore, we present evidence suggesting that an underlying pacemaker appears to oscillate at a faster frequency than the defecation cycle and that arrhythmia may result from uncoupling the pacemaker from the DMP rather than from disrupting the pacemaker itself. We also show that chronic elevations in Ca2+have limited influence on the defecation period but instead alter the interval between successive steps of the DMP. Finally, our results demonstrate that it is possible to assess Ca2+dynamics and muscular contractions in a completely unrestrained model organism.