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Ionic currents in cell's membrane: inflow of Na
C
and Cl
and outflow of K
C
Fig. 1.1
The structural component of the membrane are lipids and proteins and based on
these an explanation of its conductivity features can be provided (Fig.
1.1
). Lipids
prohibit current's conduction whereas proteins enable ions to go through them, thus
forming ion channels.
There are two types of ion channels, the gated and the non-gated ones. The non-
gated ion channels are always open. The gated ion channels switch from the open to
the closed status according to a probability that depends on the membrane's potential
(voltage-gated channels).
When the cell's membrane is in rest the gated channels remain closed and the
associated resting potential of the membrane is due only to ions getting through
the non-gated channels. When specific gates in the membrane are open there is an
inflow of Na
C
and Cl
and an outwards motion of K
C
. The inflow of ions continues
until an equilibrium condition is reached, i.e. until the concentration of positive ions
in the inner part of the membrane becomes equal to the concentration of ions to
the outer part of the membrane (equivalent is the equilibrium condition for negative
ions).
The balance mechanism in the inflow or outflow of ions is as follows: It is
assumed that there is an outflow of ions K
C
towards the outer part of the membrane.
In the inner part of the membrane there is a surplus of positive charges while in
the outer part of the membrane there is a surplus of negative charges (organic ions
A
). The outflow of the K
C
ions continues until there is an equalization of the
concentration of positive and negative charges in the inner and outer part of the
membrane.
