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#sodium

7 public questions tagged with this topic.

Membrane Transportation

Which ion has the highest intracellular concentration in most animal cells?

Ionic composition asymmetry between cytosol and extracellular fluid is actively established but reflects passive equilibrium for some ions. Primary determinant is Na+/K+ ATPase, P-type pump undergoing E1 to E2 transitions phosphorylating Asp369 in DKTGT motif, exporting three sodium and importing two potassium per ATP hydrolyzed. This creates extracellular sodium about 145 millimolar versus intracellular about 12 millimolar, and intracellular potassium about 140 millimolar versus extracellular 4 millimolar. Leak potassium channels dominated at rest maintain membrane potential near minus 90 millivolts close to EK. Chloride distribution about 110 millimolar outside versus 4 to 15 millimolar inside largely follows passive Donnan equilibrium set by impermeable anionic proteins and is modulated by K-Cl cotransporters. Calcium kept extremely low at 100 nanomolar cytosolic compared with 1 to 2 millimolar outside by SERCA sequestering into endoplasmic reticulum and PMCA extruding. Comparing abundant monovalents, potassium concentration highest inside cells, essential for enzyme activation, protein synthesis and volume regulation.

Ref: Lodish et al., Molecular Cell Biology, Section: Intracellular Ion Composition - Na+/K+ ATPase and K+ Dominance.

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Membrane Transportation

Which ion has the highest intracellular concentration in most animal cells?

Intracellular ion composition is highly asymmetric relative to extracellular fluid actively maintained using ATP to support excitability volume and enzyme function. In most mammalian cells at rest dominant intracellular cation is potassium one thirty to one forty millimolar inside versus four to five outside ten to thirtyfold gradient while sodium inverse ten to fifteen inside versus one forty five outside chloride four to twenty inside versus one ten outside bicarbonate ten inside versus twenty five outside free calcium extremely low one hundred nanomolar inside versus one point two millimolar outside twelve thousandfold plus magnesium half millimolar free. Asymmetry established primarily by continuous Na+/K+ ATPase exporting three sodium importing two potassium generating chemical and electrical gradients plus NKCC importing K+, chloride and sodium channels like Kir Kir4.1 leaking potassium to set resting potential close to potassium Nernst minus ninety millivolts. High potassium required for sixty S ribosomal peptidyl transferase pyruvate kinase maintaining negative potential counterbalancing anionic proteins buffering pH via K+/H+ exchange preventing apoptosis. Reduction triggers caspase activation and cell shrinkage during apoptosis.

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 11: Intracellular Ion Composition – High K+.

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