Electrodiffusive transport of mg across renal membrane vesicles of
the rainbow trout (oncorhynchus mykiss).
Freire, C. A., R. K. H. Kinne, E. Kinne-Saffran, and K. W. Beyenbach.
Department of Epithelial Physiology, Max-Planck-Institute for
Molecular Physiology, Rheinlanddamm 201, Dortmund 44139, Germany,
Section of Physiology, VRT 926, Cornell University, Ithaca, NY 14853
-6401
APStracts 2:0196F, 1995.
The mechanism of tubular Mg transport was investigated in membrane
vesicles (MV) of trout kidneys prepared by differential
centrifugation with sucrose. MV consisted largely of brush-border
membranes as indicated by high enrichments of brush-border membrane
enzymes. Although measured transport of 28Mg included a binding
component, most membrane transport was into or out of an osmotically
active space. There was no evidence for amiloride-sensitive Na/Mg
exchange, nor was Mg uptake affected by the carboxyl-group reagents
TMO, GME/EDAC, and DCCD, or the Ca-channel modulators D-600,
verapamil, diltiazem, and BAY K 8644. However, Mg uptake increased in
the presence of inside-negative voltages generated by either inward
gradients of the permeant anions NO3, SCN, and Cl or by outward
gradients of K (plus valinomycin). Alkaline-earth cations displayed
the selectivity sequence VII (Mg>Ca>Sr>Ba) for cis
-inhibition of 28Mg uptake. Mg efflux was trans-inhibited by La and
Gd, and Mg uptake was cis-inhibited by Mn. The sulfhydryl-group
reagents PCMB and PCMBS stimulated both Mg uptake and efflux. These
results reveal an electrodiffusive pathway for Mg transport in trout
renal MV.
Received 23 June 1995; accepted in final form 23 October 1995.
APS Manuscript Number F203-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95