membrane hyperpolarization

Definition

Target type: biologicalprocess

The process in which membrane potential increases with respect to its steady-state potential, usually from negative potential to a more negative potential. For example, during the repolarization phase of an action potential the membrane potential often becomes more negative or hyperpolarized before returning to the steady-state resting potential. [GOC:dph]

Membrane hyperpolarization is a process that increases the electrical potential difference across a cell membrane, making the inside of the cell more negative relative to the outside. This occurs due to a change in the permeability of the membrane to certain ions, most commonly potassium ions (K+).

**Mechanism of Membrane Hyperpolarization:**

* **Increased Potassium Permeability:** A key mechanism for hyperpolarization involves opening potassium channels in the cell membrane. This allows potassium ions, which carry a positive charge, to flow out of the cell. The loss of positively charged ions from the cell's interior makes the inside more negative relative to the outside.
* **Decreased Sodium Permeability:** In some cases, hyperpolarization can also be caused by a decrease in the permeability of the membrane to sodium ions (Na+). Sodium ions carry a positive charge, and reducing their influx into the cell contributes to a more negative intracellular environment.

**Role of Ion Pumps:**

* **Sodium-Potassium Pump:** This active transport mechanism plays a vital role in maintaining the concentration gradients of sodium and potassium ions across the membrane. The pump continuously pumps three sodium ions out of the cell for every two potassium ions pumped in. This contributes to the negative charge within the cell and helps establish the conditions for hyperpolarization.

**Consequences of Membrane Hyperpolarization:**

* **Reduced Excitability:** Hyperpolarization makes it more difficult for a cell to reach its threshold potential, the level of depolarization required to trigger an action potential. This reduces the cell's excitability, making it less likely to generate electrical signals.
* **Inhibition of Neurotransmitter Release:** In neurons, hyperpolarization can inhibit the release of neurotransmitters, reducing synaptic transmission.
* **Modulation of Neuronal Activity:** Hyperpolarization is a critical mechanism for regulating neuronal activity, contributing to processes such as learning and memory.

**Examples of Hyperpolarization:**

* **Afterhyperpolarization (AHP) in Neurons:** Following an action potential, a brief period of hyperpolarization known as AHP occurs, which contributes to the refractory period and helps regulate the firing rate of neurons.
* **GABAergic Inhibition:** The neurotransmitter GABA (gamma-aminobutyric acid) can induce hyperpolarization in neurons by opening chloride channels, allowing chloride ions to enter the cell and making the intracellular environment more negative.

**Summary:**

Membrane hyperpolarization is a fundamental cellular process that plays a crucial role in regulating cellular excitability, neuronal communication, and a range of physiological functions.'
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Proteins (6)

Compounds (193)