Neuronal Membrane: Ion Channels and Resting Membrane Potential

hydrophilic

dissolve in water due to uneven electrical charge

hydrophobic

does not dissolve in water due to even electrical charge

cellular fluid

intra and extra separated by the neuronal membrane

water (polar solvent) is key ingredient

ions

atoms or molecules with a net electrical charge

ion channel

made up from channel proteins

polar and nonpolar R groups

ion selectivity, ion permeability, gating property

control resting and action potentials

diffusion

dissolved ions distribute evenly, ions flow down concentration gradient

membrane potential

voltage across the neuronal membrane

resting is -65 mV

intracellular side is more negatively charged than the extracellular side

resting potential

depends upon a semi-permeable neuronal membrane, an unequal ionic distribution, “leak” K current, the Na/K pump

multiple states

characteristic of ion channel

open: allow ions to go through, have high conductance

close: prevent ion flow, low conductance

gating

characteristic of ion channels

the opening and closing of an individual ion channel is a probabilistic event, and the channel can flip between open-close states nearly instantaneously

selectivity

characteristic of ion channels

the size of the pore and the nature of the amino acid residues lining it control the permeability of ions diffusing through the channels

voltage-gated

channels open in response to changes in membrane potential

4 alpha subunits forming main channels, each subunit has 6 transmembrane domains

auxiliary proteins as regulatory subunits

ligand-gated

channels open/close in response to the binding of signal molecules

either 5 subunits with 4 transmembrane domains or g-protein with 7 transmembrane domains

gap junction

each hemi-channel is composed by 6 (repetitive) subunits

each subunit has 4 transmembrane proteins

K+ channel

4 subunits, key determinant in resting potential

equilibrium potential

depends on the charge of the ion, temperature, and ratio of external and internal ion concentrations