Propagation of Pacemaker Activity - Biopacemaking - page 113

Fig. 6. Interactions between an SAN model cell [22] and a real rabbit atrial cell. a The upper
panel shows action potentials recorded from an isolated uncoupled rabbit atrial cell ( solid line )
paced by repetitive current pulses of 2 ms duration at a basic cycle length (BCL) of 600 ms.
The dashed line shows the steady state solution of membrane potential for the SAN model cell
when the model cell is uncoupled ( G C = 0) from the real cell. The lower panel shows the
membrane potential of the atrial cell ( solid line ) and the membrane potential of the SAN model
cell ( dashed line ) for G C = 0.4 nS and no stimuli applied to the atrial cell. b The same atrial cell
with directly applied stimuli at BCL 300 ms with G C = 0 nS for the top panel and G C = 0.3 nS
in the lower panel. c Same real atrial cell paced at 600 ms with G C = 0.4 nS coupling to the
SAN model. From Joyner et al. [12].
potential of the SAN model cell (dashed line) for G C = 0.4 nS and no stimuli applied
to the atrial cell.
The coupled hybrid cell pair now has an increased CL of 437 ms (indicated by the
horizontal arrow in the lower panel), with each AP produced in the SAN model cell
accompanied, after a 52 ms delay (arrow), by a driven AP in the real atrial cell. We
investigated the effects of a range of G C for this hybrid cell pair, finding that for
values 0.4 nS there was propagation from the SAN model cell to this atrial cell with
a decreasing conduction delay as G C was increased. For G C < 0.3 nS there was
continued pacing of the SAN model without driving of the coupled atrial cell. For 0.3
< G C < 0.4 nS there was partial synchronization such that only some of the APs from
the SAN model cell were conducted to the atrial cell. In Fig. 6b we show the same