MULTI-COMPARTMENTAL REPRESENTATION OF SODIUM KINETICS IN THE VASCULAR MUSCLE BIOSYSTEM (BOUND SODIUM, MAGNESIUM DEFICIENCY, TEMPERATURE, BIOLOGICAL MODELS)
It is generally accepted that Sodium (Na('+)) in vascular muscle exists not only in a dissolved, osmotically active form, but also in a bound, osmotically inactive, form, presumably associated with the extracellular space (ECS). Although there have been attempts to define it with static studies, investigators have not yet explicitly incorporated the bound Na('+) fraction into a kinetic model. A four-compartment (bound extracellular, dissolved extracellular, dissolved intracellular, dissolved subcellular) model consonant with the bound Na('+) concept was developed to represent distribution of Na('+) in vascular muscle. In vitro washouts of rat aorta segments were performed after incubation in ('22)Na('+). A nonlinear least-squares multiexponential fit to each tracer washout curve was obtained. The multiexponential description having as parameters means of parameters of individual multiexponential fits was used to generate a prototype washout curve which was fit compartmentally. Two groups of aorta segments were studied: (1) those in which uptake and washout temperature was the only variable; (2) those obtained from rats with established dietary magnesium (Mg('2+)) deficiencies. Four prototype data records can be identified: (1) Low-temperature; (2) Normal-temperature; (3) Mg('2+)-deficient; (4) Mg('2+)-sufficient. The four-compartment model not only incorporated the bound fraction, but yielded better fits than a three-compartment model. In the temperature perturbation study, quantities of Na('+) in extracellular compartments decreased by 15% with decrease in temperature, while intra and subcellular quantities increased by 9 and 530%, respectively. Transport of Na('+) from the subcellular compartment to the intracellular compartment increased 700% while transport into the ECS was decreased with decrease in temperature. In the Mg('2+)-deficiency study, quantities of Na('+) in extracellular compartments increased slightly (3%), while intra and subcellular quantities increased by 54 and 150% in aorta from Mg('2+)-deficient rats. Transport of Na('+) from the subcellular compartment to the intracellular compartment increased 330%, as did transport into the ECS in Mg('2+)-deficient tissues.
ROBERT A MUELLER,
"MULTI-COMPARTMENTAL REPRESENTATION OF SODIUM KINETICS IN THE VASCULAR MUSCLE BIOSYSTEM (BOUND SODIUM, MAGNESIUM DEFICIENCY, TEMPERATURE, BIOLOGICAL MODELS)"
(January 1, 1986).
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