Interdisciplinary Applied Mathematics

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1. Their selectivity (what ions can pass through),


2. Their conductance (how rapidly can ions get through), and


3. Their sensitivity (how the conductance is modulated by such factors as the chemical composition of their environment, the transmembrane voltage, the membrane surface tension, and the chemical binding of the ion).


Some of the biological functions of channels include signaling and computation, triggers for cellular events, electrical power generation, energy transduction, fluid pumping and filtration, chemical sensing and mechan-otransduction.


The gating property of the ion channel:


Whenever there is a conformational change in the protein structure that lets the channel open or close, allowing the ionic current to be turned “on” or “off,” the channel is said to be gated, analogous to opening and closing of a gate. Ion channels can be classified according to which chemical or physical modulator controls their gating activity. Thus we have different groups of channels as summarized below:


1.    Ligand    gated channels:    Ligand    gated    channels    open    or    close    in    re


sponse to the binding of a small signaling molecule or “ligand.” Some ion channels are gated by extracellular ligands and others by intracellular ligands.


2. Voltage gated channels: Volt age gated channels are found in neurons and muscle cells. They open or close in response to changes in the voltage drop across the plasma membrane.


3. Mechanosensitive channels: These channels open or close in response to some mechanical deformation. For example, sound waves bending

FIGURE 13.9. A potassium channel in a lipid membrane.


the cilia-like projections on the hair cells of the inner ear open up some type of ion channels leading to the creation of nerve impulses that the brain interprets as sound.

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