Calcium‐dependent regulation of proton signaling during a rhythmic behavior in C. elegans

Abstract

In C. elegans, rhythmic defecation behavior is controlled by oscillatory Ca2+ signaling in the intestine. The first motor step in defecation requires the intestinal Na+/H+ exchanger NHX‐7, which extrudes protons through the basolateral membrane. Protons are a direct ligand for the PBO‐5 receptor on the overlying body wall muscle, and transient acidification signals the muscles to contract. This model represents the first demonstration that Na+/H+ exchangers can use protons to transmit information between cells. To test whether NHX‐7 is regulated by Ca2+ signaling, we mutated predicted Ca2+ regulatory motifs in the nhx‐7 coding region, including those for calmodulin and phosphatidylinositol 4,5‐bisphosphate binding as well as modification by various Ca2+‐activated protein kinases, then tested their ability to complement an nhx‐7(ok585) null allele. In addition, dynamic fluorescent imaging of a genetically‐encoded pH biosensor was used in these worms to measure the extent of acidification occurring between the posterior intestine and muscle cells during defecation. Finally, recombinant wildtype and mutant NHX‐7 activity was measured in tissue culture cells using conventional pharmacology and physiologic techniques. The results of these experiments provide an integrated perspective of Ca2+ and proton signaling during a model rhythmic behavior. Supported by NSF IOS0919848 (K.N.)