Ca2+ sparks in rabbit ventricular myocytes evoked by action potentials:
involvement of clusters of L-type Ca2+ channels.
Circ Res, 92 (5):
532--538 (March 2003)DOI: 10.1161/01.RES.0000064175.70693.EC
Abstract
It is not clear how many L-type Ca2+ channels (LCCs) are required
to ensure that a Ca2+ spark is triggered during a normal mammalian
action potential (AP). We investigated this in rabbit ventricular
myocytes by examining both the properties of sparks evoked by APs
and the activity of LCCs. We measured Ca2+ sparks evoked by repeated
APs with pipettes containing 2 mmol/L EGTA and single LCC activity
in cell-attached patches depolarized to +50 mV using pipettes containing
110 mmol/L Ba2+. With 2 mmol/L Ca2+ in the external solution, we
observed sparks at the beginning of every evoked AP at numerous locations.
Each spark was observed repeatedly at a fixed location and began
during a limited interval after the AP peak. These sparks occurred
with a probability of approximately unity. However, the chance that
an LCC does not open during the interval when a spark is triggered
is quite high ( approximately 0.13). Therefore, because single channels
open with a probability significantly lower than 1, more than one
LCC must be available to ensure that sparks are triggered with a
probability of approximately unity. We conclude that it is likely
that a cluster of LCCs is involved in gating a cluster of ryanodine
receptors at the beginning of an AP.
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The whole bibliography file I use.