Optical studies of membrane state during action potential propagation

Progress in Biophysics and Molecular Biology

2021

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Section: Falsification Criteria and The Role Of Optical Methodsmentioning

confidence: 99%

Section: Falsification Criteria and The Role Of Optical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Shock and detonation waves at an interface and the collision of action potentials

Progress in Biophysics and Molecular Biology

2021

“…For example, phase boundaries appear as single points in single component systems when observed as a function of a single variable, but in multicomponent system phase-boundaries exist as hypersurfaces and it is important to approach these boundaries using multiple variables for a complete understanding(70–72). For example, using solvato-chromic dyes it was recently show that in Chara Alga, the state of the membrane may change in strongly nonlinear manner as function of pH even though it changes linearly as a function of temperature (73). Relative changes in 2930 cm −1 band, both with respect to the temperature and voltage, have been found to change linearly in neurons over the limited range they have been tested.…”

Section: Challenges and Limitationsmentioning

confidence: 99%

A Thermodynamic Interpretation of the Stimulated Raman Spectroscopic Signature of an Action Potential in a Single Neuron

Lee

Cheng

2020

Preprint

It has previously been suggested that the plasma membrane condenses and melts reversibly during an action potential in a neuron. If true it has fundamental consequences for our understanding of the regulation of biological functions during an action potential. It has long been known that the electrical dipoles in the neuronal membrane reorient during an action potential, observed through a variety of optical methods. However, this information has been insufficient to confirm if and how the collective thermodynamic state of the neuronal membrane changes during an action potential. Here, we show that hyperspectral stimulated Raman spectroscopy can resolve the thermodynamic state of the neuronal membranes in a single neuron during an action potential. Based on these measurements we provide the first evidence that the system condenses during the de-polarisation phase and melts during the polarisation phase. Statement of SignificanceWhile action-potentials can be measured using a variety of methods, none of these methods have been able to provide sufficient information to characterise the collective thermodynamic state of the membrane during an action-potential. Therefore, new tools are required to satisfactorily resolve the fundamental nature of the phenomenon, i.e. does the wave-front propagates irreversibly/diffusively as in the burning of a fuse, or reversibly/elastically as in the propagation of sound. It has been postulated that if action-potentials indeed propagate elastically, then the membrane must undergo a localised condensation during the actionpotential. This article confirms and quantifies the condensation of the membrane during an action-potential based on time-resolved changes in the Raman band at 2930 cm -1 , also known as the "melting-marker".

“…the phase transition may appear different or not at all depending on the thermodynamic process and the choice of variable (15). For example, during quasi-static processes in real membranes, the state has been measured to change nonlinearly as a function of bulk pH (at constant temperature) but not temperature (at constant bulk pH) (16,17). In contrast, during an acoustic wave, both pH and temperature change (at constant entropy).…”

Section: Introductionmentioning

confidence: 99%

Shock and Detonation Waves at an Interface and the Collision of Action Potentials

2020

Preprint

Action potentials in neurons are known to annihilate each other upon collision, while there are cases where they might penetrate each other. Compression waves that travel within the plasma membrane of a neuron have previously been proposed as a thermodynamic basis for the propagation of action potentials. In this context, it was recently shown that two dimensional compressive shock waves in the model system of lipid monolayers can nearly annihilate each other upon head on collision when excited close to a phase transition. However, weaker shock waves showed penetration. In general, once the approximation of small perturbation is not valid, compression waves do not interact linearly anymore. While experiments in lipid monolayers demonstrated this principle, a mechanism remained unclear. In this article, we summarise the fundamentals of shock physics as applied to an interface and how it previously explained the observation of threshold and saturation of shockwaves in the lipid monolayer (all or none). While the theory has the same fundamental premise as the soliton model, i.e. the conservation laws and thermodynamics, we elaborate on how the two approaches make different predictions with regards to collisions and the detailed structure of the wave-front. As a case study and a new result, we show that previously unexplained annihilation of shock waves in the lipid monolayer is a direct consequence of the nature of state changes, i.e. jump conditions, within these shockwaves, and elaborate on the consequence of these results for the general understanding of the excitation waves in a thermo-fluids framework.