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Title:Characteristics of sodium transport through the amiloride-sensitive sodium-magnesium pathway in hamster red cells
Author(s):Xu, Wan Yan
Doctoral Committee Chair(s):Willis, John S.
Department / Program:Molecular and Integrative Physiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Cell
Biology, Animal Physiology
Biology, Zoology
Abstract:In hamster red cells, amiloride-sensitive Na influx, 0.8 mmol/l cell/hr, is the only, carrier-mediated, Mg-dependent pathway for inward Na transport. This Na-dependent Mg transport is involved in the regulation of intracellular Mg$\sp{2+}$ concentration under physiological conditions.
The Na-Mg transport system was studied in hamster red cells by unidirectional Na fluxes, as well as by net Mg movement. This amiloride-sensitive Na influx can be greatly stimulated by intracellular Mg$\sp{2+}$. Kinetic studies of both Na influx and Mg efflux in parallel show that a cooperative mechanism is involved in the activation by Mg$\sb{\rm i}$ with a Mg$\sb{0.5}$ of 1.7-1.8 mM and a Hill coefficient of 1.7-1.8 and that activation by Na$\sb{\rm o}$ fits a simple Michaelis-Menten equation, with a K$\sb{\rm m}$ of 83-104 mM. The similarity of the kinetics for Na and Mg activation and for amiloride inhibition (IC$\sb{50}$ = 0.3 mM) for both Na influx and net Mg loss confirm that transport of Mg$\sp{2+}$ is coupled with Na$\sp+$ with a ratio of 2 Na:1 Mg.
Amiloride-sensitive Na influx is rapidly activated by hypotonic incubation in both fresh and Mg-loaded cells. Amiloride-sensitive Na influx requires ATP. Kinase promoters, phorbol ester and dibutyl cAMP, and phosphatase inhibitors, vanadate and okadaic acid, did not stimulate amiloride-sensitive Na influx.
There was virtually no amiloride-sensitive Na efflux in hamster red cells with high (Na$\sp+$) $\sb{\rm i}$ and (Mg$\sp{2+}$) $\sb{\rm o}$, nor with hypotonicity, nor with ATP depletion.
The ATP-dependence, asymmetry of Na transport, volume dependence and apparent lack of dependence on phosphorylation mechanisms all suggest that the Na-Mg transport mechanism in hamster red cells is not a simple carrier.
Issue Date:1993
Rights Information:Copyright 1993 Xu, Wan Yan
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9411831
OCLC Identifier:(UMI)AAI9411831

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