Page 88 - YORAM RUDY BOOK FINAL

P. 88
Figure 3.9. Role of I Ca,L
in propagation during
reduced gap junction
conductance.
A. Diagram showing
direction of propagation.
B. AP upstroke at greatly
reduced gap junction
conductance g =0.020μS
j
with (solid line) and
without (dashed line)
I Ca,L . The AP shown is for
cell 1 (see diagram in A).
The bar graph shows
charge contribution to
conduction by I (Q )
Na
Na
and I Ca,L (Q Ca(L) ) during the
period from cell 1
excitation to excitation of
cell 2 (3.6 msec, marked
by the horizontal bar
above the AP). Charge
contribution from I Ca,L
approaches that from
I because the long
Na
intercellular delay
extends into the
plateau of the source
cell (cell 1), during which
I Ca,L is the major source
of depolarizing charge.
C. At extreme levels of
uncoupling, (g =0.006μS)
j
charge contribution
from I Ca,L exceeds that
from I by up to an
Na
order of magnitude and
conduction depends
strongly on I Ca,L . D. SF
with (solid line) or
without (dashed line)
I Ca,L over a range of gap
junction coupling. SF
without I Ca,L begins to
diverge at about 5-fold
decrease of coupling
(g =0.5μS). Propagation
j
without I Ca,L fails at three
times the gap junction
conductance compared
to propagation with I Ca,L.
Adapted from Shaw and
Rudy [174], with permis-
sion from Wolters
Kluwer Health, Inc.