Biomedical Engineering Reference
In-Depth Information
4 Discussion
Our study demonstrates a hyperpolarizing effect of Kir2.1 on the RMP of
neonatal cardiac myocytes by electrotonic coupling, which thereby results in
inhibition of spontaneous depolarizations of the cardiomyocytes. A remarkably
strong inhibition of the beating frequency was accomplished with relatively few
HEK-KWGF cells (Fig. 3). This may be explained by the large difference in
I
K1
densities between the two cell types, which are -60 and -8 pA/pF at -100 mV
for HEK-KWGF and NCM cells, respectively. This mechanism would be of
support to create cellular constructs consisting of a heterogeneous
population of
I
f
expressing cells and
I
K1
expressing cells, which dependent on
their relative contribution within the construct might generate a
predetermined pacemaker frequency. This approach would obviously benefit
from a controlled expression of
I
K1.
This could be reached by generating
clonal cells expressing different amounts of Kir2.1 and thereby
I
K1
Alternatively, intervention in natural Kir2.1 regulatory mechanisms could be
used, such as PKC or PKA mediated effects on
I
K1
[4, 15]. Furthermore, Kir2.1
channels appear sensitive to intracellular polyamine [10] or PIP
2
regulation [18]
which seems to operate at least in part interdependently [22]. Obvious drawback
of these approaches is the rather limited specificity of the signaling interference
which may have many undesired effects on other ion channels in the heart or
on
I
K1
in other tissues than the heart. More specific, and thus in favor, is to
produce cells in which Kir2.1 is placed under the control of an inducible
promoter, in which the inducing agent has no other physiologically relevant
biological function. To achieve this, ecdysone could be an inducer of choice [3].
The current promises in cardiac tissue engineering aside, the preclinical
research now first has to establish the applicability of proofs of principles
studies like this one, for their eventual clinical relevance.
5 Conclusion
Electrotonic coupling of Kir2.1 expressing cells to spontaneous depolarizing
NCMs results in silencing of the spontaneous beating behavior of the latter.
This system is a proof of concept demonstrating the power of electrotonic
coupling for the application of specific ion currents into an engineered cellular
construct such as a biological pacemaker.
Acknowledgments.
We thank Anatoli Lopatin for sharing Kir2.1-GFP
expression construct and Henk Rozemuller for FACS sorting of the HEK-
KWGF cells. This study is supported by the Technology Foundation (STW
program DPTE, grant #MKG5942, MvdH and grant UGT.6746, TvV), the
Netherlands Heart Foundation (grant 2003B073, TdB) and the Netherlands
Organization for Scientific Research (NWO, grant 916.36.012, TvV). FP6
(Framework Program LSHB-CT-2004-502988) of the European Committee (BK).
