Monovalent Ion Channels

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Monovalent Ion Channels
SIGMA-ALDRICH
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Monovalent Ion Channels Electrically active
cells, such as neurons and muscle cells, maintain
a resting membrane potential of approximately 70
mV. Neurotransmitters depolarize or hyperpolarize
the cell membrane by opening ion channels within
the membrane that are either an integral part of
the receptor molecule (ligand-gated ion channels)
or that are linked to the receptor through a
G-protein mediated mechanism (ion channel-linked
receptors). Occupation of the ligand recognition
site of a ligand-gated ion channel induces
changes in the conformation of the
channel-forming protein such that ion flux across
the membrane is increased. In contrast,
voltage-gated channels open or close in response
to a change in voltage across the adjacent cell
membrane. These channels are responsible for the
generation of action potentials in electrically
excitable cells. If Na permeability is
increased, Na moves into the cell down its
concentration gradient and the membrane becomes
depolarized in the region of the open channel. In
contrast, if Cl- permeability is increased, the
membrane will become hyperpolarized in the region
of the open channel. Depolarization is associated
with generation of action potentials,
degranulation, neurotransmission, and muscle
contraction. Hyperpolarization is associated with
inhibition of these processes. The resting
membrane potential is restored and maintained by
activation of the Na-K-ATPase pump that
actively extrudes Na from the cell.