Page 32 - Cardiac Electrophysiology | A Modeling and Imaging Approach

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2.7. The Purkinje Cell 93

Purkinje cells (Pcell) are characterized by different electrophysiological properties and Ca

cycling processes than ventricular myocytes (Vcell) and are frequently involved in ventricular
arrhythmias. Ultrastructurally, Pcell is devoid of transverse tubular (T-tubular) network that is
94
prominent and plays an important role in Ca handling in Vcell. Unlike Vcell, Pcell exhibits a
biphasic (double peaked) Ca transient (CaT) during an AP ; it has a complex, triple-layer spatial
2+
95
distribution of ryanodine receptor subtype 2 (RyR2) and subtype 3 (RyR3), and inositol triphos-
phate receptor subtype 1 (IP3R1) (Figure 2.18). Pcell AP is distinguished from Vcell by a faster
96
depolarization upstroke, sloping repolarization time course during phase 2 (the plateau phase in
Vcell) and longer APD 97-99 ; its underlying ion-channel profile is different from that of Vcell. These

unique electrophysiological and ultrastructural characteristics are likely the cause of differences in
rate dependence of the AP and CaT and in arrhythmic vulnerability between Pcell and Vcell.

Figure 2.18. A. Canine cardiac
Purkinje cell model. Model details
and parameters are provided in
Supplement to Reference .
93
The compartmental cell model
contains the following
compartments (from periphery
to center): peripheral coupling
subspace (PCS), subsarcolemma
(SSL), bulk myoplasm (Myo),
sarcoplasmic reticulum (SR),
junctional SR (JSR), network SR
(NSR), and corbular SR (CSR).
B. Comparison of ultrastructure
between Purkinje cell (Pcell) and
ventricular cell (Vcell). Intracellular
Ca cycling components are based
2+
on Stuyvers et al. (Pcell) and
96
Decker et al. (Vcell). Lack of
17
T-tubular network and
compartmental localization of
RyR2, RyR3, and IP R create spatial
3
heterogeneity of Ca cycling in
2+
Purkinje cells. From Li and Rudy
[93]. Reproduced with permission
from Wolters Kluwer Health, Inc.