RGD Reference Report - Electrophysiological characterization and ionic stoichiometry of the rat brain K(+)-dependent NA(+)/CA(2+) exchanger, NCKX2.

General

Electrophysiological characterization and ionic stoichiometry of the rat brain K(+)-dependent NA(+)/CA(2+) exchanger, NCKX2.
Authors:	Dong, H Light, PE French, RJ Lytton, J
Citation:	Dong H, etal., J Biol Chem. 2001 Jul 13;276(28):25919-28. Epub 2001 May 7.
RGD ID:	7175087
Pubmed:	PMID:11342562 (View Abstract at PubMed)
DOI:	DOI:10.1074/jbc.M103401200 (Journal Full-text)
We have recently described a novel K(+)-dependent Na(+)/Ca(2+) exchanger, NCKX2, that is abundantly expressed in brain neurons (Tsoi, M., Rhee, K.-H., Bungard, D., Li, X.-F., Lee, S.-L., Auer, R. N., and Lytton, J. (1998) J. Biol. Chem. 273, 4115--4162). The precise role for NCKX2 in neuronal Ca(2+) homeostasis is not yet clearly understood but will depend upon the functional properties of the molecule. Here, we have performed whole-cell patch clamp analysis to characterize cation dependences and ion stoichiometry for rat brain NCKX2, heterologously expressed in HEK293 cells. Outward currents generated by reverse NCKX2 exchange depended on external Ca(2+) with a K(12) of 1.4 or 101 microm without or with 1 mm Mg(2+), and on external K(+) with a K(1/2) of about 12 or 36 mm with choline or Li(+) as counter ion, respectively. Na(+) inhibited outward currents with a K(1/2) of about 60 mm. Inward currents generated by forward NCKX2 exchange depended upon external Na(+) with a K(1/2) of 30 mm and a Hill coefficient of 2.8. K(+) inhibited the inward currents by a maximum of 40%, with a K(1/2) of 2 mm or less, depending upon the conditions. The transport stoichiometry of NCKX2 was determined by observing the change in reversal potential as individual ion gradients were altered. Our data support a stoichiometry for rat brain NCKX2 of 4 Na(+):(1 Ca(2+) + 1 K(+)). These findings provide the first electrophysiological characterization of rat brain NCKX2, and the first evidence that a single recombinantly expressed NCKX polypeptide encodes a K(+)-transporting Na(+)/Ca(2+) exchanger with a transport stoichiometry of 4 Na(+):(1 Ca(2+) + 1 K(+)).

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Biological Process

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Term	Qualifier	Evidence	With	Reference	Notes	Source	Original Reference(s)
calcium ion transmembrane transport		IDA		7175087; 7175087		RGD

Molecular Function

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Term	Qualifier	Evidence	With	Reference	Notes	Source	Original Reference(s)
calcium, potassium:sodium antiporter activity		IDA		7175087		RGD
calcium:sodium antiporter activity		IDA		7175087		RGD

Objects Annotated

Genes (Rattus norvegicus)

Slc24a2 (solute carrier family 24 member 2)

Slc8a1 (solute carrier family 8 member A1)

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Electrophysiological characterization and ionic stoichiometry of the rat brain K(+)-dependent NA(+)/CA(2+) exchanger, NCKX2.