AJP - Renal Physiology, Vol 273, Issue 6 939-F948, Copyright © 1997 by American Physiological Society
Identification of Mg-transporting renal tubules and cells by ion microscopy imaging of stable isotopes
S. Chandra, G. H. Morrison and K. W. Beyenbach
Department of Chemistry, Cornell University, Ithaca, New York 14853, USA.
Sites of renal Mg transport were identified in seawater killifish (Fundulus
heteroclitus) using a Cameca model IMS-3f ion microscope. Killifish were
given an intraperitoneal injection of the stable isotope 26Mg (99.5%
enrichment) to stimulate and trace renal Mg excretion. We identified two
sites of 26Mg transport in frozen freeze-dried cryosections of kidney: the
proximal tubule, known to secrete Mg, and the collecting duct, heretofore
not known to handle Mg. In epithelial cells of the proximal tubule, the
punctate distribution of injected 26Mg suggests transcytotic excretion of
Mg in bound form. In collecting ducts, a subpopulation of Mg/Ca-rich cells
was identified with high accumulations of injected 26Mg. Here, the punctate
distribution of 26Mg decreased from the apical to the basal region of the
cells, revealing a transcytotic gradient of apparently bound Mg. Since
proximal tubules of fish are implicated with Mg secretion, Mg/Ca-rich cells
in the collecting duct may reabsorb Mg, thereby providing the usual
two-step of renal regulation, now also for Mg.
