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Xiao-Fang Li

Publications and source records attributed to Xiao-Fang Li.

6 recordsLinked to original sources
PubMed2006

Importance of K+-dependent Na+/Ca2+-exchanger 2, NCKX2, in motor learning and memory.

Plasma membrane Na+/Ca2+-exchangers play a predominant role in Ca2+ extrusion in brain. Neurons express several different Na+/Ca2+-exchangers belonging to both the K+-independent NCX family and the K+-dependent NCKX family. The unique contributions of each of these proteins to neuronal Ca2+ homeostasis and/or physiology remain largely unexplored. To address this question, we generated mice in which the gene encoding the abundant neuronal K+ -dependent Na+/Ca2+-exchanger protein, NCKX2, was knocked out. Analysis of these animals revealed a significant reduction in Ca2+ flux in cortical neurons, a profound loss of long term potentiation and an increase in long term depression at hippocampal Schaffer/CA1 synapses, and clear deficits in specific tests of motor learning and spatial working memory. Surprisingly, there was no obvious loss of photoreceptor function in cones, where expression of the NCKX2 protein had been reported previously. These data emphasize the critical and non-redundant role of NCKX2 in the local control of neuronal [Ca2+] that is essential for the development of synaptic plasticity associated with learning and memory.

Animals↗
PubMed2004

Differential contribution of plasmalemmal Na/Ca exchange isoforms to sodium-dependent calcium influx and NMDA excitotoxicity in depolarized neurons.

Inhibition of Na(+),K(+)-ATPase during NMDA applications greatly increased NMDA-induced excitotoxicity in primary cultures of forebrain neurons (FNs), but not in cerebellar granule cells (CGCs). Because Na(+),K(+)-ATPase inhibition promotes reversal of plasmalemmal Na(+)/Ca(2+) exchangers, we compared the activities of reversed K(+)-independent (NCX) and K(+)-dependent (NCKX) Na(+)/Ca(2+) exchangers in these cultures. To this end, we measured gramicidin-induced and Na(+)-dependent elevation in cytosolic [Ca(2+)] ([Ca(2+)](c)) that represents Ca(2+) influx via reversed NCX and NCKX; NCX activity was dissected out by removing external K(+). The [Ca(2+)](c) elevations mediated by NCX alone, and NCX plus NCKX combined, were 17 and 6 times more rapid in FNs than in CGCs, respectively. Northern blot analysis showed that FNs preferentially express NCX1 whereas CGCs expressed NCX3. Differences in expression of other isoforms (NCX2, NCKX2, NCKX3 and NCKX4) were less pronounced. We tested whether the NCX or NCKX family of exchangers contributes most to the toxic NMDA-induced Ca(2+) influx in depolarized neurons. We found that in FNs, inhibition of NCX alone was sufficient to significantly limit NMDA excitotoxicity, whereas in CGCs, inhibition of both NCX and NCKX was required. The data suggest that the high activity of NCX isoforms expressed in FNs, possibly NCX1, sensitizes these neurons to NMDA excitotoxicity.

Animals↗
PubMed2003

[The evolution and application of microsatellites].

Microsatellites,simple sequence repeats (SSR),are abundant and distributed throughout the eukaryote genome. The contents of microsatellites are variant in different creatures. There are also different types of microsatellites, which are dominant in different creatures. One of the most noticeable characters of microsatellites is that they are easy to expand during DNA replication. It is thought to attribute to DNA slippage. This kind of mutation is affected by many factors. It is guessed that microsatellites come from pro-microsatellites, while the pro-microsatellites origin from random point mutations. The length of microsatellites can be maintained under relative conservative ranges during species evolution. As they are abundant, codominatnt,distributed over the euchromatic part of the genome, and have the character of highly polimorphic, microsatellites are useful tools for gene mapping, clinical diagnosis and predicting, paternity or pedigree analysis, evolution study, and marker-assisted breeding.

English Abstract↗
PubMed2002

Molecular cloning of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4.

We report here the identification and characterization of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4 (gene SLC24A4), which mapped to the chromosomal region 14q32. Human NCKX4 encoded a protein of 605 amino acids that displayed a high level of sequence identity to previously described family members, rod NCKX1 (gene SLC24A1), cone/neuronal NCKX2 (gene SLC24A2), and ubiquitous NCKX3 (gene SLC24A3), in the hydrophobic regions surrounding the alpha-repeat sequences thought to form the ion-binding pocket used for transport. The protein product of the NCKX4 gene shared the highest level of amino acid identity, as well as an almost identical arrangement of exon boundaries, with NCKX3, indicating that these two genes have arisen from a recent duplication event. NCKX4 transcripts were abundantly expressed in all brain regions, aorta, lung, and thymus, as well as at a lower level in many other tissues. The NCKX4 protein demonstrated potassium-dependent sodium calcium exchanger activity when assayed in transfected HEK293 cells using digital imaging of fura-2 fluorescence. The discovery of NCKX4, as far as can be ascertained from the current version of the human genome sequence, completes the mammalian potassium-dependent sodium-calcium exchanger gene family.

Amino Acid Sequence↗
PubMed2002

Preferential expression of plasmalemmal K-dependent Na+/Ca2+ exchangers in neurons versus astrocytes.

Numerous isoforms of plasmalemmal K-dependent (NCKX) and K-independent (NCX) Na+/Ca2+ exchangers are expressed in the brain. The physiological functions of each isoform are presently unknown. Therefore, in this study, we compared expression of NCKX and NCX transcripts between primary cultures of cerebellar granule cells, and astrocytes. Northern blot analysis showed that granule cells expressed NCKX2, NCKX3, NCKX4 and NCX3, whereas astrocytes expressed primarily NCX1. Consistent with this molecular characterization, a significant fraction of 45Ca2+ accumulation in Na-loaded granule cells, but not in astrocytes, depended on external K+. This is the first demonstration of native NCKX activity in neurons derived from the central nervous system. Our data suggest that NCKX isoform expression may correspond to the unique Ca2+ homeostasis requirements of neurons.

Animals↗