Abstract
We have characterized modulation of ICa by Ca$^2+$ at the t-tubules
(ie, in control cells) and surface sarcolemma (ie, in detubulated
cells) of cardiac ventricular myocytes, using the whole-cell patch
clamp technique to record ICa. ICa inactivation was significantly
slower in detubulated cells than in control cells (27.1+/-7.8 ms,
n=22, versus 16.4+/-7.9 ms, n=22; P<0.05). In atrial myocytes, which
lack t-tubules, ICa inactivation was not changed by the treatment
used to produce detubulation. In the presence of ryanodine or BAPTA,
or when Ba2+ was used as the charge carrier, the rate of inactivation
was not significantly different in control and detubulated cells.
Frequency-dependent facilitation occurred in control cells but not
in detubulated cells, and was abolished by ryanodine. These results
suggest that Ca$^2+$ released from the SR has a greater effect
on ICa in the t-tubules than at the surface sarcolemma. This does
not appear to be due to differences in local Ca$^2+$ release
from the SR, because the gain of Ca$^2+$ release was not significantly
different in control and detubulated cells. These data suggest that
the t-tubules are a key site for the regulation of transsarcolemmal
Ca$^2+$ flux by Ca$^2+$ release from the SR; this could play
a role in altered Ca$^2+$ homeostasis in pathological conditions.
The full text of this article is available online at http://circres.ahajournals.org.
- 15192026
- animals,
- calcium
- calcium,
- cardiac,
- cell
- cells,
- channels,
- conductivity,
- cultu,
- electric
- gov't,
- heart
- l-type,
- membrane,
- myocytes,
- non-u.s.
- patch-clamp
- rats,
- red,
- research
- reticulum,
- sarcoplasmic
- support,
- techniques,
- ventricles,
- wistar,
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