Abstract
We are studying both Na:Ca exchange stoichiometry and cytosolic Ca
(Cai)-dependent regulation of Na-Ca exchange (NCX) in intact rabbit
ventricular myocytes. Analysis of NCX fluxes in subcellular systems
strongly supports a dominant 3Na:1Ca exchange, and our measurements
in intact cells confirm this. However, in intact native cells, local
ion gradients and other factors complicate the process of inferring
stoichiometry. From a functional viewpoint, NCX stoichiometry is
near 3:1 but is affected by ion accumulation/depletion as well as
non-NCX fluxes. We and others have viewed Cai-dependent NCX regulation
as a static process (dependent on instantaneous local Cai). However,
evidence from subcellular and expression systems shows the process
to be dynamic, and our observations confirm this to be the case in
intact cardiac cells as well.
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