Osmotic pressure in body fluids is highly regulated in vertebrates, but the sensing mechanisms for such control have not been identified. One possible sensing mechanism involves sensors for tension in membranes. Indeed, in Caenorhabditis elegans, the OSM-9 protein, a putative ion channel, confers sensitivity to osmotic pressure, touch, and certain odorants. Liedtke et al. screened for vertebrate homologs of this protein and obtained cDNAs for rat, mouse, human, and chicken versions of the vanilloid receptor-related osmotically activated channel or VR-OAC. When expressed in Chinese hamster ovary cells, the rat or chicken orthologs conferred Ca2+ influx that was sensitive to small changes in transmembrane osmotic pressure. Expression of the putative osmoreceptor was detected in multiple locations, consistent with its function in physiological sensing of osmotic pressure.
Liedtke, W., Choe, Y., Marti-Renom, M.A., Bell, A.M., Denis, C.S., Sali, A. Hudspeth, A. J., Friedman, J.M., and Heller, S. (2000) Vanilloid receptor-related osmotically activated channel (VR-OAC), a candidate vertebrate osmoreceptor. Cell 103: 525-535. [Online Journal]