Biomedical Engineering Reference
In-Depth Information
features, Andersen syndrome patients may suffer from cardiac arrhythmias.
Therefore, unlike mice, large animal species, including man, may be more
vulnerable for a loss of
I
K1
from the heart with respect to the occurrence of
arrhythmias. In principle, introduction of a dominant negative form of Kir2.1
in the working myocardium may undermine a stable resting membrane
potential (RMP), and thereby increase vulnerability of the cell for membrane
potential fluctuations, which may eventually result in a spontaneous
depolarization. Dependent upon the size of such an unstable region, a real
local pacemaker able to drive the heart may be formed. In guinea pig, where a
more prominent role for Kir2.1 in ventricular cardiomyocyte membrane
potential stabilization is suspected than in mice, a strong ectopic expression
of dominant negative forms of Kir2.1 indeed leads to liberation of pacemaker
activity in the ventricle [9].
Although introduction of potent dominant negative Kir2.1 may result in
biological pacemaker activity, the disadvantage is its dependence on
spontaneous membrane potential fluctuations rather than on pacemaker currents
formed by the HCN family. A similar situation can be found in embryonic
stem cell pacemaker action. During stem cell differentiation into cardio-
myocytes, the developmental program is recapitulated resulting in
spontaneously beating cells. In the P19 cell model, only a minority of the cells
expresses functional
I
f
, and no
I
K1
is found in such cells [21] from which it can
be concluded that pacemaker behavior occurs through RMP fluctuations
allowed by the absence of the inward rectifier. Upon maturation, however, some
cells start to express
I
K1
, which is accompanied by stable, more negative
RMPs and a cessation of spontaneous beating. The uncontrolled maturation
of embryonic stem cell derived cardiomyocytes makes them currently unsuitable
for use as biological pacemakers. A promising avenue seems to use a cell-based
tissue construct delivering HCN-mediated
I
f
to the surrounding myocardium
[12]. Such a biological pacemaker cell construct needs to be tightly controlled,
and we hypothesized that biologically engineered ion channel expressing cells
could attribute to biological pacemaker regulation through electrotonic
coupling. Here, we demonstrate, as a proof of principle, that
I
K1
expressing
HEK-293 cells can modulate the beating frequency of spontaneously active
neonatal rat cardiomyocytes through electronic interaction.
2 Methods
2.1 HEK-KWGF Cells and Neonatal Cardiomyocytes
HEK-293 cells (ATCC # CRL-1573) were regularly cultured in DMEM
supplemented with 10% fetal calf serum, 2 mM
L
-glutamine, 50 U/ml
penicillin, and 50 µg/ml streptomycin, all purchased from Cambrex
(Verviers, Belgium).
