Biomedical Engineering Reference
In-Depth Information
110 cycles/min. Mice were then anesthetized with isoflurane (0.5-1.5%) under con-
trolled ventilation with the respirator for the remainder of the surgical procedure. A
left thoracotomy was performed between ribs four and five, and the pericardial sac
was removed. Isolated EGFP (+) cells that had been expanded for 5 days were resus-
pended in phosphate-buffered saline at a concentration of 5 ×·10
7
cells/ml. A cell sus-
pension volume of 50 ȝl was drawn into a 50 ȝl Hamilton syringe with a 31-gauge
needle, and 10 ȝl was injected into the anterior wall of the left ventricle. Injection of
phosphate-buffered saline was used as a control.
2.9 Statistical Analysis
Values are presented as mean ± SEM. The significance of differences between means
was determined by ANOVA. Comparison of the control and treated groups was car-
ried out using the non-parametric Fisher's multiple comparison tests. The accepted
level of significance was P < 0.05.
3 Results
3.1 Temporal Changes of the Action Potentials in Bone Marrow-Derived
Cardiomyocytes
To characterize the action potentials of the bone marrow-derived cardiomyocytes, we
first recorded the action potentials of differentiated CMG cells at 2-5 weeks after
treatment. Cardiomyocyte-like action potentials recorded from these spontaneously
beating cells had (1) relatively long action potential durations or plateaus, (2) rela-
tively shallow resting membrane potentials, and (3) pacemaker-like late diastolic slow
depolarizations. Action potentials were distinctly sinus node-like (Fig. 1a) or ven-
tricular myocyte-like (Fig. 1b). The sinus node-like action potentials had shallower
resting membrane potentials and more marked late diastolic slow depolarizations, like
pacemaker potentials. The ventricular myocyte-like action potentials had peak- and
dome-like morphologies.
The two distinct types of action potential in CMG cells may reflect different devel-
opmental stages. Figure 1c shows how the proportions of sinus node-like and ven-
tricular myocyte-like action potentials changed over successive weeks. Until 3 weeks,
all of the action potentials recorded from CMG cells were sinus node-like. The ven-
tricular myocyte-like action potentials were recorded from 4 weeks, and the percent-
age of these action potentials progressively increased there after. These findings sug-
gested that bone marrow-derived cardiomyocytes showed temporal changes indicative
of maturation.
3.2 Expression of K
+
Cannels in CMG Cells
Cardiomyocytes have a wide variety of K
+
currents, including
I
K1
,
I
to
,
I
Kr
,
I
Ks
,
I
K
,
Ach
, and
I
K,ATP
. To begin to address the expression of inward rectifying K
+
(
I
K1
) channels,
we first investigated expression of their constituting subunits Kir2.1 and Kir2.2 using
