Biomedical Engineering Reference
In-Depth Information
amplitudes being 136 and 105 mV, respectively. These values are comparable to our
previous experimental data [9] for the resting membrane potential, amplitude and
maximum d
V
/d
t
measured from ten isolated rabbit atrial cells (-80 ± 1 mV, 109 ± 3
mV, and 206 ± 17 V/s, respectively) which differed significantly (p < 0.05) from
those values we measured from six isolated rabbit ventricular cells (-82.7 ± 0.4 mV,
127 ± 1.12 mV, and 395 ± 21 V/s, respectively). Several fundamental differences in
the membrane currents are included in these models. These differences include a
lower value of maximum sodium conductance, lower value of the inward rectifier
current (
I
K1
), and greater transient outward current for the atrial model compared to
the ventricular model and these differences are based on experimental data as
described in the model papers.
Fig. 7. a
Diagram of the experimental setup in which a 7 × 7 array of cells is represented by a
real central focus cell (isolated cell from the atrioventricular nodal area) is coupled to model
elements which are real-time simulations of mathematical models of either ventricular or atrial
cells (Luo and Rudy model [17] for ventricular cells, Courtemanche et al. model [6] for atrial
cells). The coupling conductances (nS) in the X or Y directions are assumed to be constant and
identical (
G
X
=
G
Y
).
b
Summary of results obtained from eight real isolated atrioventricular
nodal cells by coupling each cell into atrial model arrays and ventricular model arrays with
coupling conductances of 10, 20, 30, or 40 nS and varying the size factor of the real nodal cell
to determine the critical size which allows spontaneous activity of the nodal cell with
propagation into each model array with each value of coupling conductance. For
G
X
=
G
Y
= 10
nS only 4 of the 8 nodal cells tested were able to successfully propagate into the V model array
at any of the sizes (up to 100) tested. Data are shown as mean ± SEM for the V model arrays
(
solid triangles
) and the A model arrays (
open triangles
). From Joyner et al. [15].
For these studies, we isolated spontaneously active myocytes from the rabbit
atrioventricular node region and then coupled a real nodal cell into a real-time
simulation of a small sheet of cells with specified electrical coupling in the
X
and
Y
directions, as shown in Fig. 7a. From eight spontaneously active cells, the average CL
when uncoupled was 340 ± 52 ms, with a maximum diastolic depolarization of -65 ±
8 mV, a peak positive amplitude of 36 ± 9 mV, and a maximum d
V
/d
t
of the rising
phase of 13.6 ± 3.9 V/s. In the experimental protocol, we allowed the real nodal cell
