Localization of Mg 2+ -sensing shark kidney calcium receptor SKCaR in kidney of spiny dogfish, Squalus acanthias

• Published in: American journal of physiology. Renal physiology 2003-09, Vol.285 (3), p.F430-F439
• Main Authors: Hentschel, Hartmut, Nearing, Jacqueline, Harris, H. William, Betka, Marlies, Baum, Michelle, Hebert, Steven C., Elger, Marlies
• Format: Article
• Language: English
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.00081.2002

We recently cloned a homologue of the bovine parathyroid calcium receptor from the kidney of a spiny dogfish ( Squalus acanthias) and termed this new protein SKCaR. SKCaR senses alterations in extracellular Mg 2+ after its expression in human embryonic kidney cells (Nearing J, Betka M, Quinn S, Hentschel H, Elger M, Baum M, Bai M, Chattopadyhay N, Brown E, Hebert S, and Harris HW. Proc Natl Acad. Sci USA 99: 9231-9236, 2002). In this report, we used light and electron microscopic immunocytochemical techniques to study the distribution of SKCaR in dogfish kidney. SKCaR antiserum bound to the apical membranes of shark kidney epithelial cells in the following tubular segments: proximal tubules (PIa and PIIb), late distal tubule, and collecting tubule/collecting duct as well as diffusely labeled cells of early distal tubule. The highly specific distribution of SKCaR in mesial tissue as well as lateral countercurrent bundles of dogfish kidney is compatible with a role for SKCaR to sense local tubular Mg 2+ concentrations. This highly specific distribution of SKCaR protein in dogfish kidney could possibly work in concert with the powerful Mg 2+ secretory system present in the PIIa segment of elasmobranch fish kidney to affect recycling of Mg 2+ from putative Mg 2+ -sensing/Mg 2+ -reabsorbing segments. These data provide support for the possible existence of Mg 2+ cycling in elasmobranch kidney in a manner analogous to that described for mammals.