Submitted on February 26, 2002
Accepted on May 13, 2003
Localization of Mg2+-sensing shark kidney calcium receptor SKCaR in kidney of dogfish, Squalus acanthias
Hartmut Hentschel1*, Jacqueline Nearing2, H. William Harris2, Marlies Betka2, Michelle Baum3, Steven C. Hebert4, and Marlies Elger5
1 AG Hentschel, Max-Planck-Institut mol. Physiol., Dortmund, Germany; Mount Desert Island Biological Laboratory, Salsbury Cove, Maine, USA
2 MariCal LLC, Portland, Maine, USA
3 Childrens Hospital Boston, Boston, Massachusetts, USA
4 Yale University School of Portland, New Haven, Connecticut, USA
5 Department of Nephrology, Medizinische Hochschule Hannover, Hannover, Germany
* To whom correspondence should be addressed. E-mail: hartmut.hentschel{at}mpi-dortmund.mpg.de.
We have recently cloned a homologue of the bovine parathyroid calcium receptor (BoPCaR) from the kidney of spiny dogfish, Squalus acanthias and termed this new protein SKCaR. SKCaR senses alterations in extracellular magnesium (Mg2+) after its expression in human embryonic kidney (HEK) cells. [Nearing, J., et. al. Proc. Nat. Acad. Sci. (USA) 99:9231-9236 (2002)]. In this report, we used light and electron microscopy immunocytochemical techniques to study SKCaR's distribution 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 (LDT) and collecting tubule-collecting duct (CT/CD) as well as diffusely labelled cells of early distal tubule (EDT). SKCaR's highly specific distribution in the mesial tissue (MT)as well as lateral countercurrent bundles (LB)of dogfish is compatible with a role for SKCaR to sense the local tubular Mg2+ -concentrations. This highly specific distribution of SKCaR protein in dogfish kidney could possibly work in concert with the powerful Mg2+ secretory system present in the PIIa segment of elasmobranch fish to affect recycling of Mg2+ from putative Mg2+ -sensing/Mg2+ reabsorbing segments. These data provide support for the possible existence of Mg2+ cycling in elasmobranch kidney in a manner analogous to that described for mammals.
