Biomedical Engineering Reference
In-Depth Information
Table 4.1 Comparison of conductance induced by single channel measured from discrete current
jumps and calculated using empirical equations
Conductance/
channel calculated
by discrete steps
(nS)
Conductance/
channel calculated
using the empirical
equations (nS)
No. of
Independent
experiments Buffer solutions
Buffer
conductivity
(mS cm
1
)
2
5 mM Tris + 0.5 M
NaCl
1.65
0.07
(
n ¼
44.6
1.72
62)
6
5 mM Tris + 1 M NaCl 3.04
0.56
(
n ¼
76.3
2.79
52)
3
5 mM Tris + 2 M NaCl 4.71
0.18
(
n ¼
130.9
4.64
45)
40
TMS + 1 M NaCl
3.14
0.36
(
n ¼
500)
80.5
2.94
2
5 mM HEPES + 0.5 M
KCl
2.48
0.13
(
n ¼
10)
54.4
2.73
4
5 mM HEPES + 1 M
KCl
4.73
0.20 (
n ¼
9)
99.7
4.49
Note
: The conductance in Table was calculated using the ratio of the measured current jump
induced by a discrete step to the applied voltage. “(
n
)” in column three represents the number
of insertions
A formula specific to the phi29 system can be derived for calculating the single
channel conductance. A plot of solution conductivity,
s
b
(measured with a
Corning conductivity meter) versus single channel conductance (obtained from
the slopes of the regression equations) revealed a linear relationship (Fig.
4.6e, f
).
Using the regression equations,
G
c
at NaCl or KCl concentration within the
range 0.5-2.0 M can be deduced from buffer conductivity,
s
b
.
The NaCl buffer conductivity is given by:
s
b; NaCl
ðmS cm
1
G
c
;
NaCl
nS
ðR
2
Þ
¼
29
:
58
6
:
32
¼
0
:
9994
Þ
(4.2)
s
b; NaCl
ðmS cm
1
Þ
þ
6
:
32
G
c
;
NaCl
nS
Thus,
¼
29
:
58
Similarly, the KCl buffer conductivity can be obtained as follows:
s
b; KCl
ðmS cm
1
G
c
;
KCl
nS
ðR
2
Þ
¼
25
:
69
15
:
61
¼
0
:
9923
Þ
(4.3)
s
b; KCl
ðmS cm
1
Þ
þ
15
:
61
G
c
;
KCl
nS
¼
Thus,
25
:
69
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