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Modeling osmotic transients during exercise
Author(s) -
Christmas Kevin M,
Jensen Austin,
Bassingthwaighte James
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.860.2
Subject(s) - osmotic concentration , osmole , extracellular fluid , chemistry , extracellular , biophysics , osmosis , intracellular fluid , body fluid , osmotic pressure , medicine , endocrinology , biochemistry , biology , membrane
The body maintains tight osmotic regulation despite deviations from homeostasis at rest or during intense exercise. Maintaining osmotic equilibrium can result in exercising muscle reducing plasma volume by 10–15% depending on intensity, the mass of tissue stimulated, and mode of exercise. Research often references this phenomenon with reduced plasma volume or increased plasma osmolarity during exercise, but more correctly whole body osmolarity goes up with volume shifts occurring in all tissues. Elevated muscle osmolarity from exercising metabolism results in water flux into active muscle from the extracellular compartment, causing muscle cells to swell, decreasing plasma volume, and hemoconcentrating the blood. Assuming all solutes are fixed, impermeable to membranes, we can calculate the increase in extracellular osmolarity due to volume loss from a normal value of 280 mOsM to ~329 mOsM. Assuming de novo formation of intramuscular solutes, exercising metabolism would have to increase the muscle osmolarity by ~94 mM to produce this volume shift, assuming none leaves the cell. This rise in muscle osmolarity results in water influx, diluting the cells concentration to match the bodies osmolarity of 329 mOsM. These simple algebraic calculations fail to incorporate tissue mass, diffusion of metabolic substrates out of the muscle, or anatomical representation of a working human. During intense exercise a 70‐kilogram man generates an osmotic gradient shifting over a liter of fluid towards muscle within 30–60 seconds. Metabolically, glycolytic intermediates are prime candidates with muscle lactate concentration rising ten fold during intense exercise, but cannot be the only factor of importance. This model quantifies osmotic water flux due to metabolic byproducts of glycolysis and ATP breakdown with whole body osmotic balance and recirculation. Additional products of muscle metabolism need to be identified to explain the water fluxes during short term exercise. Support or Funding Information Research supported by NIH grants NHLBI T15 088516 and U01‐HL122199, and NIBIB EB08407.