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Dynamics of cell membrane passive depolarization: a phase portrait
Gaetano L Aiello1, Enrico Bignetti, Carlo Casarino
1Universita di Palermo, Italy, Dipartimento di Fisica e Tecnologie Relative, Viale delle Scienze, Ed. 18, Palermo , 90128, Italy.
Nonlinear Dynamics, Psychology, and Life Sciences
|June 19, 2007
Summary
Blocking ionic pumps in cells does not lead to zero membrane voltage. Instead, a 3-ion model shows it causes a negative voltage and sodium gradient inversion, crucial for cell revival.
Area of Science:
- Cellular Biology
- Nonlinear Dynamics
- Biophysics
Background:
- Persistent blockage of ionic pumps is a critical factor in cell membrane potential dynamics.
- Understanding the steady-state behavior of cell membranes under pump inhibition is essential for cellular health.
Purpose of the Study:
- To investigate the effect of sustained ionic pump blockage on cell membrane voltage.
- To explore the nonlinear dynamics governing ionic concentration changes and membrane potential.
- To determine if chemical equilibrium is reached or if a gradient inversion occurs.
Main Methods:
- A 3-ion model was developed based on continuity and charge conservation principles.
- Experimental validation using PC12 cells incubated with Oubaine for 24 hours.
- Analysis of ionic concentrations and membrane voltage dynamics in a 3D phase space.
Main Results:
- The 3-ion model predicts that membrane voltage stabilizes at a negative value, not zero.
- Experimental results show a significant increase in cytosolic Na+ (266 mM/l), supporting Na+ gradient inversion.
- The dynamics of depolarization exhibit unique topological features in the ionic concentration space.
Conclusions:
- Chemical equilibrium is not reached; instead, a reversal of the Na+ concentration gradient occurs hours after pump blockage.
- Late repolarization of Na+-K+ pumps can lead to cell revival.
- Depolarization-repolarization cycles display complex dynamics, potentially leading to phase space wandering or closed loops.
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The action potential is a complex electrical event that occurs in excitable cells, such as neurons and muscle cells. It consists of several distinct phases, each with specific characteristics.
Resting Phase:
In this phase, the cell's membrane is at its resting potential, typically around -70 millivolts (mV) for neurons. Inside the cell, there is a higher concentration of potassium ions (K+) and a lower concentration of sodium ions (Na+). Voltage-gated sodium channels are closed, and...
Resting Phase:
In this phase, the cell's membrane is at its resting potential, typically around -70 millivolts (mV) for neurons. Inside the cell, there is a higher concentration of potassium ions (K+) and a lower concentration of sodium ions (Na+). Voltage-gated sodium channels are closed, and...
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Overview
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The resting membrane potential of a neuron (-70mV) is sustained due to the selective ion permeability of the membrane. At the resting potential, the membrane is slightly permeable to ions like sodium (Na+) and chloride (Cl−) and highly permeable to potassium ions (K+). Differences in the ions' concentration inside the cell compared to the outside are maintained by membrane transport proteins like channels and pumps.
At rest, the K+ is the main ion that moves across the membrane through...
At rest, the K+ is the main ion that moves across the membrane through...