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#sodium-potassium pump

16 public questions tagged with this topic.

Membrane Transportation

What is the primary function of Na+/K+ ATPase in maintaining secondary active transport?

Primary role of Na+/K+ ATPase in context of secondary active transport is generation and maintenance of electrochemical sodium gradient that powers numerous symporters and antiporters. By pumping three Na+ outward and two K+ inward per ATP hydrolyzed, it creates chemical gradient low intracellular Na+ and electrical gradient interior negative near minus 70 mV. Combined sodium motive force represents stored free energy. Solute carrier families SLC5 SGLT, SLC6 neurotransmitter transporters, SLC38 amino acid transporters, SLC9 NHE and SLC8 NCX exploit this force allowing Na+ to move downhill while accumulating glucose, amino acids, phosphate or extruding H+ and Ca2+ uphill. Without pump activity Na+ accumulates intracellularly, gradient collapses, concentrative nutrient absorption in gut and kidney fails, pH regulation falters, calcium overload occurs via reverse Na+/Ca2+ exchanger. Ouabain inhibition illustrates dependence. Thus pump does not directly carry glucose but indirectly energizes secondary systems, explaining coupling between primary and secondary active transport in animal cells for nutrient uptake and homeostasis.

Ref: Alberts et al., 7th ed., Chapter 11, Na+/K+ pump and secondary transport coupling.

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Membrane Transportation

The Na+/K+ ATPase pump operates by exchanging:

Active maintenance of sodium and potassium gradients consumes significant portion of cellular ATP budget, about one third in neurons, mediated by Na+/K+ ATPase discovered by Skou. P-type pump cycle begins in E1 conformation with ion binding site open to cytoplasm high affinity for sodium, coordinating three sodium ions using side chain carboxyls of Glu327, Glu776, Asp804 and backbone carbonyls in M4-M6. ATP binds N domain, phosphorylates Asp369 in P domain forming E1P occluded state. Transition to E2P lowers sodium affinity releasing ions extracellularly where sodium about 145 millimolar. Cavity now reorganized high affinity for potassium accommodating two potassium ions via similar carbonyl coordination requiring smaller dehydration energy. Potassium binding triggers dephosphorylation by A domain TGES motif generating E2 with occluded K+ then conversion to E1 opening intracellular releasing K+ where affinity weak. Net exchange three Na+ outward, two K+ inward per ATP, electrogenic exporting one positive charge, contributing to negative interior and enabling secondary active processes like SGLT and NCX. Inhibitor ouabain binds E2P extracellular vestibule.

Ref: Morth et al., Nature 2007, Crystal Structure of Na+/K+ ATPase Stoichiometry 3Na+ Out 2K+ In.

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Membrane Transportation

Which of the following ATP-powered pumps is responsible for maintaining resting membrane potential?

Resting membrane potential stability essential for excitability maintained by differential permeability and active ion distribution. Key player is Na+/K+ ATPase, P-type ion pump encoded by ATP1A genes for alpha isoforms, ATP1B for beta, FXYD for gamma regulatory. Catalytic alpha subunit roughly 112 kDa with ten membrane spans contains nucleotide N domain binding ATP, phosphorylation P domain with conserved DKTGTLT aspartate that forms phosphoenzyme intermediate, actuator A domain and transmembrane ion binding pocket coordinating ions with carbonyl oxygens. Cycle Post-Albers: E1 high Na affinity intracellular binding three Na+, phosphorylation to E1P occluding, transition to E2P outward low Na affinity releasing, high K affinity binding two K+, dephosphorylation to E2, return. Electrogenic 3 out 2 in adds minus 3 millivolts directly plus creates gradients enabling K+ leak through Kv and Kir producing minus 70 to minus 90 millivolts. V-type pumps acidify lysosomes, F-type synthesizes ATP, ABC exporters expel drugs. Only P-class Na+/K+ ATPase directly maintains gradients underlying resting potential.

Ref: Skou and Glynn, P-Type ATPases Review, Na+/K+ ATPase Role in Resting Membrane Potential Maintenance.

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Membrane Transportation

The Na+/K+ ATPase pump is an example of:

Coupled transporters classified as antiporters exchange substrates in opposite directions driven by gradients. Sodium potassium ATPase exemplifies primary active antiporter using ATP rather than secondary gradient. Alpha subunit has ten transmembrane helices forming pocket with three sodium sites and two potassium sites. It binds three intracellular Na+ in high affinity E1 and exports them while binding two extracellular K+ and importing them, so Na+ and K+ move opposite in same cycle. Exchange is electrogenic due to 3:2 stoichiometry, contributing about minus four millivolts to potential and producing outward current measurable in voltage clamp. Antiport contrasts with symport where solutes travel same direction as Na+-glucose symport and uniport where single solute moves passively. Mechanistically antiporters use alternating-access rocker-switch where binding of one substrate lowers affinity for other enforcing exchange in many secondary transporters, while ATPase cycle allows slippage under nonphysiological conditions. E1 to E2 conformational change alternates binding site exposure, coupling ATP hydrolysis to opposing movements essential for excitability and volume control.

Ref: Skou & Esmann, Journal of Bioenergetics 1992: Na+,K+-ATPase as Antiporter Mechanism.

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Membrane Transportation

The Na+/K+ ATPase pump transports:

Sodium-potassium pump is archetypal P-type ATPase maintaining electrochemical gradients vital for volume control and excitability. Each cycle hydrolyzes one ATP to ADP and phosphate, driving conformational shift from E1 high Na+ affinity inward to E2 low affinity outward via phosphorylated Asp369 intermediate. In E1 facing cytosol, cavity binds three sodium ions, triggering autophosphorylation. Transition to E2-P exposes cavity extracellularly where Na+ affinity drops, sodium released and potassium sites exposed. Two extracellular potassium ions bind with high affinity in E2-P, inducing dephosphorylation returning to E1 where potassium released inside due to low affinity. Net result is outward movement of three Na+ and inward two K+ per ATP, generating net outward positive current and inside-negative potential around minus seventy millivolts, preventing swelling and providing high internal K+ favoring ribosome function. This gradient fuels secondary transporters like Na+/Ca2+ and Na+/H+ exchangers and action potential recovery. Cardiac glycosides ouabain and digoxin inhibit by binding E2-P state, raising intracellular Na+.

Ref: Skou & Esmann, Journal of Bioenergetics 1992: Na+,K+-ATPase Stoichiometry – 3 Na+ out, 2 K+ in.

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