| Summary: | Posterior body wall muscle contraction (pBoc) in the nematode Caenorhabditis elegans occurs rhythmically every 45 – 50 s and mediates defecation. pBoc is controlled by inositol-1,4,5-trisphosphate (IP 3) – dependent Ca 2+ oscillations in the intestine. The intestinal epithelium can be studied by patch clamp electrophysiology, Ca 2+ imaging, genome-wide reverse genetic analysis, forward genetics, and molecular biology and thus provides a powerful model to develop an integrated systems level understanding of a nonexcitable cell oscillatory Ca 2+ signaling pathway. Intestinal cells express an outwardly rectifying Ca 2+ (ORCa) current with biophysical properties resembling those of TRPM channels. Two TRPM homologues, GON-2 and GTL-1, are expressed in the intestine. Using deletion and severe loss-of-function alleles of the gtl-1 and gon-2 genes, we demonstrate here that GON-2 and GTL-1 are both required for maintaining rhythmic pBoc and intestinal Ca 2+ oscillations. Loss of GTL-l and GON-2 function inhibits I ORCa � 70 % and � 90%, respectively. I ORCa is undetectable in gon-2;gtl-1 double mutant cells. These results demonstrate that (a) both gon-2 and gtl-1 are required for ORCa channel function, and (b) GON-2 and GTL-1 can function independently as ion channels, but that their functions in mediating I ORCa are interdependent. I ORCa, I GON-2, and I GTL-1 have nearly identical biophysical properties. Importantly, all three channels are at least 60-fold more permeable to Ca 2+ than Na +. Epistasis analysis suggests that GON-2 and GTL-1 function in the IP 3 signaling pathway to regulate intestinal Ca 2+ oscillations. We postulate that GON-2 and GTL-1 form heteromeric ORCa channels that mediate selective Ca 2+ influx and function to regulate IP 3 receptor activity and possibly to refill ER Ca 2+ stores.
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