K+-dependent Na+/Ca2+ exchanger 3 is involved in renal active calcium transport and is differentially expressed in the mouse kidney

Regulation of K+-Dependent Na+/Ca2+-Exchangers (NCKX)

Potassium-dependent sodium-calcium exchangers (NCKX) have emerged as key determinants of calcium (Ca²⁺) signaling and homeostasis, especially in environments where ion concentrations undergo large changes, such as excitatory cells and transport epithelia. The regulation of NCKX transporters enables them to respond to the changing cellular environment thereby helping to shape the extent and kinetics of Ca²⁺ signals. This review examines the current knowledge of the different ways in which NCKX activity can be modulated. These include (i) cellular and dynamic subcellular location (ii); changes in protein expression mediated at the gene, transcript, or protein level (iii); genetic changes resulting in altered protein structure or expression (iv); regulation via changes in substrate concentration (v); and post-translational modification, partner protein interactions, and allosteric regulation. Detailed mechanistic understanding of NCKX regulation is an emerging area of research with the potential to provide important new insights into transporter function, the control of Ca²⁺ signals, and possible interventions for dysregulated Ca²⁺ homeostasis.

Organ‑specific expression of the divalent ion channel proteins NCKX3, TRPV2, CTR1, ATP7A, IREG1 and HEPH in various canine organs

Transmembrane cation channels include those for calcium, copper and iron ion transport. Each channel has physiological significance, and all have been associated with disease. However, the comparative study of transcriptional‑translational levels in canine organs has not been previously reported. In the present study, organ‑specific expression of calcium channels, including sodium/potassium/calcium exchanger 3 (NCKX3) and transient receptor potential cation channel subfamily V member 2 (TRPV2), copper channels, including high affinity copper uptake protein 1 (CTR1) and copper‑transporting ATPase 1 (ATP7A), and iron channels, including iron‑regulated transporter 1 (IREG1) and hephaestin (HEPH) proteins and their mRNAs were examined in the canine duodenum, kidney, spleen and liver. NCKX3 protein expression was highest in the kidney, moderate in the duodenum, and lowest in the spleen and liver, whereas TRPV2 protein was highly expressed in the kidney, duodenum and liver, and was low in the spleen. The CTR1 protein expression level was highest in the liver, followed (in descending order) by the duodenum, kidney and spleen. The ATP7A protein expression level was highest in the duodenum and lowest in the spleen. The IREG1 protein expression level was highest in the liver, followed (in descending order) by the kidney, duodenum and spleen. The HEPH protein level was high in liver, moderate in the duodenum and kidney, and low in the spleen. The results of the immunohistochemistry analysis demonstrated ion channel protein localizations. These results suggested that cation channel proteins are differentially expressed among canine organs, and they may be involved in organ‑specific functions associated with the maintenance of physiological homeostasis.

NCKX3 was compensated by calcium transporting genes and bone resorption in a NCKX3 KO mouse model

Gene knockout is the most powerful tool for determination of gene function or permanent modification of the phenotypic characteristics of an animal. Existing methods for gene disruption are limited by their efficiency, time required for completion and potential for confounding off-target effects. In this study, a rapid single-step approach to knockout of a targeted gene in mice using zinc-finger nucleases (ZFNs) was demonstrated for generation of mutant (knockout; KO) alleles. Specifically, ZFNs to target the sodium/calcium/potassium exchanger3 (NCKX3) gene in C57bl/6j were designed using the concept of this approach. NCKX3 KO mice were generated and the phenotypic characterization and molecular regulation of active calcium transporting genes was assessed when mice were fed different calcium diets during growth. General phenotypes such as body weight and plasma ion level showed no distinct abnormalities. Thus, the potassium/sodium/calcium exchanger of NCKX3 KO mice proceeded normally in this study. As a result, the compensatory molecular regulation of this mechanism was elucidated. Renal TRPV5 mRNA of NCKX3 KO mice increased in both male and female mice. Expression of TRPV6 mRNA was only down-regulated in the duodenum of male KO mice. Renal- and duodenal expression of PTHR and VDR were not changed; however, GR mRNA expression was increased in the kidney of NCKX3 KO mice. Depletion of the NCKX3 gene in a KO mouse model showed loss of bone mineral contents and increased plasma parathyroid hormone, suggesting that NCKX3 may play a role in regulating calcium homeostasis.

Multiple Calcium Export Exchangers and Pumps Are a Prominent Feature of Enamel Organ Cells

Calcium export is a key function for the enamel organ during all stages of amelogenesis. Expression of a number of ATPase calcium transporting, plasma membrane genes (ATP2B1-4/PMCA1-4), solute carrier SLC8A genes (sodium/calcium exchanger or NCX1-3), and SLC24A gene family members (sodium/potassium/calcium exchanger or NCKX1-6) have been investigated in the developing enamel organ in earlier studies. This paper reviews the calcium export pathways that have been described and adds novel insights to the spatiotemporal expression patterns of PMCA1, PMCA4, and NCKX3 during amelogenesis. New data are presented to show the mRNA expression profiles for the four Atp2b1-4 gene family members (PMCA1-4) in secretory-stage and maturation-stage rat enamel organs. These data are compared to expression profiles for all Slc8a and Slc24a gene family members. PMCA1, PMCA4, and NCKX3 immunolocalization data is also presented. Gene expression profiles quantitated by real time PCR show that: (1) PMCA1, 3, and 4, and NCKX3 are most highly expressed during secretory-stage amelogenesis; (2) NCX1 and 3, and NCKX6 are expressed during secretory and maturation stages; (3) NCKX4 is most highly expressed during maturation-stage amelogenesis; and (4) expression levels of PMCA2, NCX2, NCKX1, NCKX2, and NCKX5 are negligible throughout amelogenesis. In the enamel organ PMCA1 localizes to the basolateral membrane of both secretory and maturation ameloblasts; PMCA4 expression is seen in the basolateral membrane of secretory and maturation ameloblasts, and also cells of the stratum intermedium and papillary layer; while NCKX3 expression is limited to Tomes' processes, and the apical membrane of maturation-stage ameloblasts. These new findings are discussed in the perspective of data already present in the literature, and highlight the multiplicity of calcium export systems in the enamel organ needed to regulate biomineralization.

Isoforms of Spectrin and Ankyrin Reflect the Functional Topography of the Mouse Kidney

The kidney displays specialized regions devoted to filtration, selective reabsorption, and electrolyte and metabolite trafficking. The polarized membrane pumps, channels, and transporters responsible for these functions have been exhaustively studied. Less examined are the contributions of spectrin and its adapter ankyrin to this exquisite functional topography, despite their established contributions in other tissues to cellular organization. We have examined in the rodent kidney the expression and distribution of all spectrins and ankyrins by qPCR, Western blotting, immunofluorescent and immuno electron microscopy. Four of the seven spectrins (αΙΙ, βΙ, βΙΙ, and βΙΙΙ) are expressed in the kidney, as are two of the three ankyrins (G and B). The levels and distribution of these proteins vary widely over the nephron. αΙΙ/βΙΙ is the most abundant spectrin, found in glomerular endothelial cells; on the basolateral membrane and cytoplasmic vesicles in proximal tubule cells and in the thick ascending loop of Henle; and less so in the distal nephron. βΙΙΙ spectrin largely replaces βΙΙ spectrin in podocytes, Bowman’s capsule, and throughout the distal tubule and collecting ducts. βΙ spectrin is only marginally expressed; its low abundance hinders a reliable determination of its distribution. Ankyrin G is the most abundant ankyrin, found in capillary endothelial cells and all tubular segments. Ankyrin B populates Bowman’s capsule, podocytes, the ascending thick loop of Henle, and the distal convoluted tubule. Comparison to the distribution of renal protein 4.1 isoforms and various membrane proteins indicates a complex relationship between the spectrin scaffold, its adapters, and various membrane proteins. While some proteins (e.g. ankyrin B, βΙΙΙ spectrin, and aquaporin 2) tend to share a similar distribution, there is no simple mapping of different spectrins or ankyrins to most membrane proteins. The implications of this data are discussed.

The SLC24 gene family of Na⁺/Ca²⁺-K⁺ exchangers: from sight and smell to memory consolidation and skin pigmentation

Members of the SLC24 gene family encode K(+)-dependent Na(+)/Ca(2+) exchangers (NCKX) that utilize both the inward Na(+) and outward K(+) gradients to extrude Ca(2+) from cells. There are five human SLC24 genes that play a role in biological process as diverse as vision in retinal rod and cone photoreceptors, olfaction, skin pigmentation and at least three of the five genes are also widely expressed in the brain. Here I review the functional, physiological and structural features of NCKX proteins that have emerged in the past few years.

Change of genes in calcium transport channels caused by hypoxic stress in the placenta, duodenum, and kidney of pregnant rats

Preeclampsia is a pregnancy-specific disease characterized by concurrent development of hypertension, proteinuria, and oxidative stress in the placenta. In this study, we induced hypoxic stress in rats during pregnancy to reproduce physiological conditions associated with preeclampsia. The maternal weight of hypoxic pregnant rats was lower than that of normoxic animals. The level of calcium ions were also increased in urine collected from the hypoxic animals. In contrast, urinary concentrations of sodium, chloride, and potassium ions declined in hypoxic rats, and developed to proteinuria. The expression of genes known as two biomarkers, sFLT1 (for preeclampsia) and HIF-1alpha (for hypoxia), were highly induced in the placenta, duodenum, and kidney by hypoxic stress. The overexpression of sFLT1 and HIF-1alpha demonstrated that our experimental conditions closely mimicked ones that are associated with preeclampsia. In the present study, we measured the expression of calcium transporters (TRPV5, TRPV6, PMCA1, NCKX3, NCX1, and CaBP-9k) in the placenta, duodenum, and kidney under hypoxic conditions on Gestational Day 19.5 in rats. Placental TRPV5, TRPV6, and PMCA1 expression was up-regulated in the hypoxic rats, whereas the levels of NCX1 and CaBP-9k were unchanged. In addition, NCKX3 expression was increased in the placenta of hypoxic rats. Duodenal expression of CaBP-9k, TRPV5, TRPV 6, and PMCA1 was decreased in the hypoxic rats, whereas levels of NCXs were not altered. Renal expression of NCKX3 and TRPV6 was increased, whereas NCX1 was decreased in the hypoxic rats compared to the normoxic controls. Taken together, these results indicate that physiological changes observed in the hypoxic rats were similar to ones associated with preeclampsia. Expression of calcium transport genes in the placenta, duodenum, and kidney perturbed by hypoxic stress during pregnancy may cause calcium loss in the urine, and thereby induce calcium-deficient characteristics of preeclampsia.

Genes involved in vasoconstriction and vasodilation system affect salt-sensitive hypertension

The importance of excess salt intake in the pathogenesis of hypertension is widely recognized. Blood pressure is controlled primarily by salt and water balance because of the infinite gain property of the kidney to rapidly eliminate excess fluid and salt. Up to fifty percent of patients with essential hypertension are salt-sensitive, as manifested by a rise in blood pressure with salt loading. We conducted a two-stage genetic analysis in hypertensive patients very accurately phenotyped for their salt-sensitivity. All newly discovered never treated before, essential hypertensives underwent an acute salt load to monitor the simultaneous changes in blood pressure and renal sodium excretion. The first stage consisted in an association analysis of genotyping data derived from genome-wide array on 329 subjects. Principal Component Analysis demonstrated that this population was homogenous. Among the strongest results, we detected a cluster of SNPs located in the first introns of PRKG1 gene (rs7897633, p = 2.34E-05) associated with variation in diastolic blood pressure after acute salt load. We further focused on two genetic loci, SLC24A3 and SLC8A1 (plasma membrane sodium/calcium exchange proteins, NCKX3 and NCX1, respectively) with a functional relationship with the previous gene and associated to variations in systolic blood pressure (the imputed rs3790261, p = 4.55E-06; and rs434082, p = 4.7E-03). In stage 2, we characterized 159 more patients for the SNPs in PRKG1, SLC24A3 and SLC8A1. Combined analysis showed an epistatic interaction of SNPs in SLC24A3 and SLC8A1 on the pressure-natriuresis (p interaction = 1.55E-04, p model = 3.35E-05), supporting their pathophysiological link in cellular calcium homeostasis. In conclusions, these findings point to a clear association between body sodium-blood pressure relations and molecules modulating the contractile state of vascular cells through an increase in cytoplasmic calcium concentration.