structures. The signal from receptor flows through cellular signal transducing system. This system exists in most of cells because neuronal system and hormonal
system use receptor on each cell for communication among cells. Hormone as
cellular communication signal is secreted by hormone secretory cell and neuro
transmitter is secreted by axon terminal and it is received by receptor on a post
synaptic cell. Cell membrane (biomembrane) has properties of compartmentation
and selective permeation. The selective permeation is due to channel or pump
protein. Permeation of specific ion generated concentration difference between
inside and outside of membrane, and it triggers action potential of neuron. Pump
protein actively transports ions against chemical potential by use of energy. It plays
key role for maintaining membrane potential. H
+ ATPase, one of pump proteins
generate ATP from ADP and phosphate by rotation of rotator using concentration
difference of proton. Molecular structure of a potassium ion channel is obtained by
X-ray diffraction study and relationship between selective permeation of K
+ and
structure of channel path was elucidated [13].
2.7 Membrane Potential
There are various ions in biological body including cells, and ionic environment is
different in both sides of biomembrane. And the difference of ionic concentrations
generates membrane potential. Membrane proteins of channel and pump selectively
permeate corresponding ions. So, change of membrane potential correlates various
biological functions of cells. From view point of physical chemistry, concentration
of substance generates chemical potential. In a case that substance is ion, membrane
potential is also generated in addition to chemical potential. And electro chemical
potential is represented by the following equation. μ 0 , C i , z, F and φ are , standard
electrochemical potential, concentration of ion species i, electric charge, Faraday
constant and membrane potential, respectively.
μi ¼ μ0 þ RT ln Ci þ zFφ
When there are ions which are unable to permeate membrane in one side of the
membrane. Donnan potential is generated in equilibrium state. Donnan equilibrium
potential E is represented by following equation.
E ¼ φ out À φ in ¼
RT
F
ln
CKin
CKout
¼
RT
F
ln
CClout
CClin
A cell has negatively charged and impermeable proteins inside of it. Considering
this case in the presence of permeable ions of K
+ and Cl
-, the impermeable proteins
generate different concentrations of these ions between inside and outside of
2.7 Membrane Potential
25
system use receptor on each cell for communication among cells. Hormone as
cellular communication signal is secreted by hormone secretory cell and neuro
transmitter is secreted by axon terminal and it is received by receptor on a post
synaptic cell. Cell membrane (biomembrane) has properties of compartmentation
and selective permeation. The selective permeation is due to channel or pump
protein. Permeation of specific ion generated concentration difference between
inside and outside of membrane, and it triggers action potential of neuron. Pump
protein actively transports ions against chemical potential by use of energy. It plays
key role for maintaining membrane potential. H
+ ATPase, one of pump proteins
generate ATP from ADP and phosphate by rotation of rotator using concentration
difference of proton. Molecular structure of a potassium ion channel is obtained by
X-ray diffraction study and relationship between selective permeation of K
+ and
structure of channel path was elucidated [13].
2.7 Membrane Potential
There are various ions in biological body including cells, and ionic environment is
different in both sides of biomembrane. And the difference of ionic concentrations
generates membrane potential. Membrane proteins of channel and pump selectively
permeate corresponding ions. So, change of membrane potential correlates various
biological functions of cells. From view point of physical chemistry, concentration
of substance generates chemical potential. In a case that substance is ion, membrane
potential is also generated in addition to chemical potential. And electro chemical
potential is represented by the following equation. μ 0 , C i , z, F and φ are , standard
electrochemical potential, concentration of ion species i, electric charge, Faraday
constant and membrane potential, respectively.
μi ¼ μ0 þ RT ln Ci þ zFφ
When there are ions which are unable to permeate membrane in one side of the
membrane. Donnan potential is generated in equilibrium state. Donnan equilibrium
potential E is represented by following equation.
E ¼ φ out À φ in ¼
RT
F
ln
CKin
CKout
¼
RT
F
ln
CClout
CClin
A cell has negatively charged and impermeable proteins inside of it. Considering
this case in the presence of permeable ions of K
+ and Cl
-, the impermeable proteins
generate different concentrations of these ions between inside and outside of
2.7 Membrane Potential
25