Abstract
Here, we address three issues in intact ventricular myocytes that
specifically relate to the role of Na/Ca exchange (NCX) current under
physiological conditions. First, we revisit the issue of NCX stoichiometry
in light of some recent findings that the stoichiometry of the NCX
may not be fixed at 3Na: 1Ca. We discuss some data that strongly
favor the 3:1 stoichiometry, at least under physiological conditions.
Second, we address the controversy over the role of allosteric Ca
regulation in intact myocytes. We show that outward and inward I(NCX)
can be activated dynamically by changing Ca(i) over the physiological
range and that outward I(NCX) can be activated quite rapidly with
sarcoplasmic reticulum Ca release. These data are well described
using an instantaneous equation for NCX current that includes an
allosteric activation factor with K(mCaAct) = 125 nM. Finally, we
consider the effect on NCX current of submembrane elevations in Ca(i)
(that are far greater than are measured in the bulk cytoplasm). Taken
together with a NCX stoichiometry of 3, these findings have allowed
us to make some predictions of the role of I(NCX) during an AP. Our
simulations suggest that NCX current is outward for less than approximately
10 ms at the beginning of the action potential.
- 12502604
- allosteric
- animals,
- calcium,
- cells,
- exchanger,
- gov't,
- heart
- humans,
- kinetics,
- membrane
- muscle
- non-u.s.
- p.h.s.,
- potentials,
- regulation,
- research
- sodium,
- sodium-calcium
- support,
- u.s.
- ventricles,
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