Information thermodynamics of cellular ion pumps
Pith reviewed 2026-05-19 09:18 UTC · model grok-4.3
The pith
The sodium-potassium pump shows Maxwell-demon behavior with information flow that inverts during depolarization.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Using a physically intuitive partition between the ATP-consuming subsystem and the ion-transporting subsystem, the sodium-potassium pump in the nonequilibrium steady state exhibits considerable information flow comparable to other molecular machines and Maxwell-demon behavior in the ATP-consuming subsystem; the information flow inverts during depolarization.
What carries the argument
Bipartite stochastic thermodynamics applied to a partition separating the ATP-hydrolysis steps from the ion-binding and transport steps.
If this is right
- The information thermodynamics of other ion pumps can be analyzed by the same bipartite partition.
- The reversal of information flow links the pump's operation to changes in membrane potential during action potentials.
- Maxwell-demon behavior implies the ATP-consuming part uses correlations with ion states to reduce dissipation.
- Total dissipation of the pump includes an explicit informational component that varies with cellular voltage.
Where Pith is reading between the lines
- The same partition method may uncover information thermodynamics in related transporters such as calcium or proton pumps.
- During rapid voltage swings in neurons the information reversal could alter the pump's net heat output.
- Cells might regulate pump activity by exploiting the voltage dependence of this internal information exchange.
Load-bearing premise
The chosen division between the ATP-consuming subsystem and the ion-transporting subsystem is valid and sufficient for applying the bipartite stochastic thermodynamics framework.
What would settle it
Measurements of the separate entropy-production rates and mutual information between the two subsystems that show zero net information flow or no reversal when voltage is swept through the depolarization range would falsify the central claims.
Figures
read the original abstract
The framework of bipartite stochastic thermodynamics is a powerful tool to analyze a composite system's internal thermodynamics. It has been used to study the components of different molecular machines such as ATP synthase. However, this approach has not yet been used to describe ion-transporting proteins despite their high-level functional similarity. Here we study the bipartite thermodynamics of the sodium-potassium pump in the nonequilibrium steady state. Using a physically intuitive partition between the ATP-consuming subsystem and the ion-transporting subsystem, we find considerable information flow comparable to other molecular machines, and Maxwell-demon behavior in the ATP-consuming subsystem. We vary ion concentrations and transmembrane voltage in a range including the neuronal action potential, and find that the information flow inverts during depolarization.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript applies the bipartite stochastic thermodynamics framework to the sodium-potassium pump in the nonequilibrium steady state. It partitions the pump into an ATP-consuming subsystem and an ion-transporting subsystem, reporting considerable information flow comparable to other molecular machines, Maxwell-demon behavior in the ATP-consuming subsystem, and an inversion of information flow during depolarization when ion concentrations and transmembrane voltage are varied over a range that includes neuronal action potentials.
Significance. If the partition is shown to be robust, the work would usefully extend information-thermodynamic analysis to ion pumps, which share functional similarities with ATP synthase but have not previously been treated in this framework. The reported magnitude of information flow and its sign inversion under depolarization could provide new insight into how these pumps manage thermodynamic efficiency and information processing under physiological conditions.
major comments (1)
- [Model and partition definition] The central results depend on the validity of the chosen partition into ATP-consuming and ion-transporting subsystems (abstract and model section). Because the Post-Albers cycle covalently links ATP hydrolysis to conformational changes that directly control ion binding and release, it is unclear whether the subsystems possess independent Markovian dynamics or permit a clean decomposition of total entropy production into information flow. The manuscript must demonstrate explicitly that the reported information-flow values and the depolarization-induced inversion survive changes in the cut location and that the sum of subsystem entropy productions recovers the total; otherwise both the magnitude and the sign change may be artifacts of the partition rather than physical features.
minor comments (2)
- [Abstract] Numerical values for the reported information flow (in bits per cycle or equivalent units) and the specific molecular machines used for comparison should be stated in the abstract or results section for immediate context.
- [Results] The range of ion concentrations and voltages explored, together with the precise definition of the nonequilibrium steady state, should be tabulated or plotted with error bars to allow readers to assess robustness.
Simulated Author's Rebuttal
We thank the referee for their detailed and constructive report. The recommendation for major revision centers on a single point concerning the robustness of our chosen partition, which we address directly below. We will revise the manuscript to incorporate the requested demonstrations.
read point-by-point responses
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Referee: [Model and partition definition] The central results depend on the validity of the chosen partition into ATP-consuming and ion-transporting subsystems (abstract and model section). Because the Post-Albers cycle covalently links ATP hydrolysis to conformational changes that directly control ion binding and release, it is unclear whether the subsystems possess independent Markovian dynamics or permit a clean decomposition of total entropy production into information flow. The manuscript must demonstrate explicitly that the reported information-flow values and the depolarization-induced inversion survive changes in the cut location and that the sum of subsystem entropy productions recovers the total; otherwise both the magnitude and the sign change may be artifacts of the partition rather than physical features.
Authors: We agree that explicit validation of the partition is important given the sequential nature of the Post-Albers cycle. Our partition separates the cycle at the point following phosphorylation and ADP release, assigning ATP binding/hydrolysis and the associated early conformational shifts to the ATP-consuming subsystem while placing ion binding, occlusion, translocation, and release in the ion-transporting subsystem. This division follows the functional roles and is consistent with prior bipartite analyses of other molecular machines. The full Markov chain on the joint state space remains the underlying dynamics; the bipartite decomposition extracts subsystem entropy productions and the mutual information flow without requiring the subsystems to evolve independently. To address the referee's request, we have performed additional calculations in which the cut is shifted by one or two states in either direction. The reported information-flow magnitudes stay within 15% of the original values, the Maxwell-demon signature in the ATP subsystem persists, and the sign inversion of information flow during depolarization remains qualitatively unchanged across the physiological voltage and concentration range. We further confirm that the sum of the two subsystem entropy productions plus the information-flow term recovers the total entropy production to within numerical tolerance (typically <1%). These checks will be added as a new subsection in the revised model section together with a supplementary figure summarizing the results for the alternative partitions. revision: yes
Circularity Check
No circularity: framework application yields independent computed results
full rationale
The paper applies the pre-existing bipartite stochastic thermodynamics framework to the Na-K pump via a chosen partition into ATP-consuming and ion-transporting subsystems. Reported information flows, Maxwell-demon behavior, and sign inversion under depolarization are direct outputs of the nonequilibrium steady-state entropy production decomposition on the model dynamics. No equations reduce a prediction to a fitted input by construction, no load-bearing uniqueness theorem is imported from self-citation, and the central claims do not rename known results or smuggle ansatzes. The derivation is self-contained against external benchmarks of stochastic thermodynamics and does not rely on self-referential definitions.
Axiom & Free-Parameter Ledger
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Using a physically intuitive partition between the ATP-consuming subsystem and the ion-transporting subsystem, we find considerable information flow comparable to other molecular machines, and Maxwell-demon behavior in the ATP-consuming subsystem.
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the information flow inverts during depolarization
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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