Biomedical Engineering Reference
In-Depth Information
Table 7.1
Average parameter values
Name
Value
Units
10
−
6
s
−
1
Apical sodium conductance (
Pa
Na
)
2
.
2
×
cm
·
10
−
7
s
−
1
Apical potassium conductance (
Pa
K
)
4
.
0
×
cm
·
10
−
6
s
−
1
Apical chloride conductance (
Pa
Cl
)
1
.
6
×
cm
·
10
−
7
s
−
1
Apical bicarbonate conductance (
Pa
HCO
3
)
1
.
6
×
cm
·
10
−
6
s
−
1
Basolateral potassium conductance (
Pb
K
)
6
.
0
×
cm
·
10
−
7
s
−
1
Basolateral chloride conductance (
Pb
Cl
)
1
.
0
×
cm
·
Na
+
-
n
HCO
3
cotransporter permeability (
G
Na
−
HCO
3
)
10
−
6
cm
2
1
.
5
×
mol
/
s
/
cm
−
2
Pump current (
I
max
)
20
µ
A
·
Sodium Affinity (
k
Na
i
)
10
mM
n
Hill
3
P
mol
·
cm
−
2
·
s
−
1
Na-K-2Cl cotransporter (trCl)
10
1
.
0
×
10
−
8
cm
·
s
−
1
Na shunt permeability (
P
Na
s
)
1
.
0
×
10
−
8
cm
·
s
−
1
K shunt permeability (
P
K
s
)
1
.
0
×
10
−
8
cm
·
s
−
1
Cl shunt permeability (
P
Cl
s
)
10
−
9
s
−
1
.
×
·
HCO
3
shunt permeability (
P
HCO
3
s
)
2
0
cm
Coupling ratio in Na-
n
HCO
3
cotransporter (
n
Co
)
2
Effective charge of unloaded carrier (
zL
)
1
Velocity constant ratio (
R
lk
)
100
Na
+
dissociation constant (
K
c
Na
)
500
mM
HCO
3
dissociation constant (
K
c
HCO
3
)
30
mM
e
−
(
1
−
n
)
×
F
×
Na
+
]
c
[
HCO
3
]
n
c
R
l
/
k
×
[
PD
bl
2
RT
B
=
+
K
c
Na
K
c
HCO
3
1
HCO
3
]
Na
+
]
bl
K
c
Na
Na
+
]
bl
[
n
bl
+
[
+
[
×
K
c
Na
K
c
HCO
3
Table
7.1
lists the values of parameters used in the model, while Table
7.2
lists the
average values used for different parameters and ionic concentrations as a starting
point in the model.
The model computes the flow of ions across a layer of epithelial cells, the cel-
lular currents, the amounts of different ions being secreted and other electrogenic
properties of different ion transporters. By understanding the above, we can better
understand the mechanisms that lead to ion imbalances, such as those during the flu,
or more serious conditions such as cystic fibrosis. Another important use of the model
is to test the effects of new drugs on the system. Besides testing, the model can help
us hypothesize new mechanisms for future drug action. Affecting one channel has a
direct effect on the way other ion channels behave. In case of cystic fibrosis, we may
be able to compensate for low bicarbonate and chloride conductivity by affecting the
permeability of other channels.
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