Biomedical Engineering Reference
In-Depth Information
6.5
Noninvasive and Real-Time Monitoring of Cell Functions
6.5.1
Metabolism
Glucose-stimulated electrical activity in pancreatic “-cells was provided as evidence
of cell electrical activity [
39
-
49
], although muscle and nerve cells were believed
to be specialized cells with electrical excitability. After the investigation, numerous
works on the electrophysiology of “-cells were carried out and it has been elucidated
[
50
-
52
]. The patch-clamp technique makes it possible to demonstrate the channels
that contribute to the generation of electrical activity. The adenosine triphosphate
(ATP) regulated K
C
channels (K
AT P
channels) provide the crucial link between
metabolic and electrophysiological effects of glucose. K
C
flows out of the cell
through spontaneously active K
AT P
channels at low glucose and ATP concentrations.
The K
C
gradients existing over the “-cell membrane results in a negative membrane
potential of approximately -70 mV. Increasing glucose concentrations subsequently
elevates intracellular ATP concentrations and closes K
AT P
channels. Moreover, the
generation of electrical activity is a key step in glucose-induced insulin release, and
it is widely thought to represent the primary mechanism by which Ca
2
C
is imported
into the “-cell cytosol, causing an increase in intracellular Ca
2
C
concentration and
triggering several processes that ultimately result in insulin exocytosis [
53
].
Basically, the semiconductor-based biosensing device that was used in this study
is an ion-sensitive field-effect transistor (IS-FET), which has been commonly used
as a pH sensor [
3
]. The principle of IS-FET is based on the direct detection of hydro-
gen ion concentration based on the site-binding model [
54
] at the gate insulator,
as also described above. On the other hand, the glucose-induced insulin secretion
process includes the activation of ATP generation, which is closely related to
respiration activity in the mitochondrion. The induction of respiration activity would
increase hydrogen ion concentration at the cell/gate interface because of CO
2
release
in solutions [
55
]. As a result of activation of respiration, the increase of hydrogen
ion concentration at the cell/gate interface will be directly detected as pH variation
using IS-FET. In this section, we introduce the real-time, label-free, and noninvasive
monitoring of electrical activity of rat pancreatic “-cells using a cell-based FET,
focusing on the correlation between respiration activity accompanied by insulin
secretion process due to glucose induction and electrical activity of pancreatic
“-cells.
Rat pancreatic “-cells (RIN-5F) were used for the electrical detection of glucose
response using the FETs in the present study. The “-cells were introduced to the
sensing areas of the FET chip in a culture medium RPMI1640 medium, pH 7.4
(Invitrogen) including 2 mg/ml glucose supplemented with 10 % fetal bovine serum
(FBS; JRH Biosciences) and 1 % penicillin/streptomycin (Invitrogen) at 37
ı
in an
atmosphere of 5.0 % CO
2
for 3 days after being maintained on a culture dish with
the controlled RPMI1640 medium at 37
ı
in an atmosphere of 5.0 % CO
2
for 1 week.
In the electrical measurements, 400 l of controlled medium without glucose was
placed in the FET chamber, and 10 mg/ml glucose was added to the culture medium
