Highly Ca2+-selective TRPM channels regulate IP3-dependent oscillatory Ca2+ signaling in the C. elegans intestine.
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 (IP3)-dependent Ca2+ oscillations in the intestine. The intestinal epithelium can be studied by patch clamp electrophysiology, Ca2+ 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 Ca2+ signaling pathway. Intestinal cells express an outwardly rectifying Ca2+ (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 Ca2+ oscillations. Loss of GTL-l and GON-2 function inhibits I(ORCa) approximately 70% and approximately 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 Ca2+ than Na+. Epistasis analysis suggests that GON-2 and GTL-1 function in the IP3 signaling pathway to regulate intestinal Ca2+ oscillations. We postulate that GON-2 and GTL-1 form heteromeric ORCa channels that mediate selective Ca2+ influx and function to regulate IP3 receptor activity and possibly to refill ER Ca2+ stores.
Xing
Juan
J
Department of Anesthesiology, Vanderbilt University Medical Center,Nashville, TN 37232, USA.
Yan
Xiaohui
X
Estevez
Ana
A
Strange
Kevin
K
D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D005786:Gene Expression Regulation; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007811:Lanthanum / Q000378:metabolism / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D050053:TRPM Cation Channels / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D050053:TRPM Cation Channels; D007811:Lanthanum; D015544:Inositol 1,4,5-Trisphosphate; D008274:Magnesium; D002118:Calcium