Characteristics of sodium transport through the amiloride-sensitive sodium-magnesium pathway in hamster red cells
Xu, Wan Yan
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https://hdl.handle.net/2142/21375
Description
Title
Characteristics of sodium transport through the amiloride-sensitive sodium-magnesium pathway in hamster red cells
Author(s)
Xu, Wan Yan
Issue Date
1993
Doctoral Committee Chair(s)
Willis, John S.
Department of Study
Molecular and Integrative Physiology
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Cell
Biology, Animal Physiology
Biology, Zoology
Language
eng
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.
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