Countertransport Activity Research Articles

Model-fitting and linkage analysis of sodium-lithium countertransport.

Increased sodium-lithium countertransport activity (SLC) associates with hypertension and is highly heritable, yet the underlying genes remain unknown. SLC, measured on 1113 and remeasured 2-3 years later on 675 adult members of 48 Utah pedigrees, was tested for candidate gene association, major locus inheritance, and linkage to genome scan markers using a bivariate model with genotype-specific effects of age, body mass index (BMI), and triglycerides level (TG). No effect of the alpha-adducin Gly460Trp polymorphism on SLC was found. In contrast, SLC increased with age in carriers of apolipoproteinE varepsilon2 (85 individuals; 8.7% of the sample) and decreased in noncarriers. Model-fitting analyses inferred two additional loci with genotype-specific responses to BMI and TG. Using the inferred model, lod scores >2 were obtained for D3S3038, D11S4464, and D10S677 for the BMI-responsive locus, and for D8S1048 for the TG-responsive locus.

Increased sodium-lithium countertransport activity: a cellular dysfunction common to essential hypertension and diabetic nephropathy.

An increased activity of sodium-lithium countertransport (SLC) is a common finding in patients who have essential hypertension. The evidence that a similar dysfunction is shared also by patients with type 1 diabetes and nephropathy has suggested the hypothesis that a predisposition to essential hypertension may be the factor that, along with hyperglycemia, underlies the development of diabetic nephropathy. Despite the initial enthusiasm surrounding the potential use of SLC activity as a marker for the early detection and treatment of individuals who are predisposed to hypertension and diabetic nephropathy, its use has been so far restricted to epidemiologic studies, as specificity and sensitivity of the test are still too low to justify any clinical use. The recent finding, however, that the measurement of kinetic parameters of SLC can significantly increase the power to discriminate among individuals with and without hypertension or diabetic nephropathy could be of help toward a future clinical use of the measurement of this membrane transport. A second major point relates to the possibility that SLC per se might be directly involved in the pathogenesis of essential hypertension and diabetic nephropathy. This case has never been fully tested, as the gene responsible for this membrane transport has been, until recently, unknown. The recent identification of an alternative splicing of the first isoform of Na-H exchange that mediates SLC activity should allow for a rapid comprehension of the role of this transport in the pathophysiology of essential hypertension and diabetic nephropathy.

Involvement of OCTN1 (SLC22A4) in pH-Dependent Transport of Organic Cations

OCTN1 (SLC22A4) transports cationic compounds such as tetraethylammonium in a pH-sensitive and sodium-independent manner in cultured cells, and is expressed in wide variety of tissues, including kidney, muscle, placenta, heart, and others. This study focused on the clarification of its subcellular distribution in kidney and on its driving force to throw light on the pharmacological and physiological roles of OCTN1. Uptake of [14C]tetraethylammonium by membrane vesicles prepared from HEK293 cells stably transfected with human OCTN1 cDNA was osmolarity-sensitive, and the Km of tetraethylammonium was 1.28 mM at intravesicular and extravesicular pH values of 6.0 and 7.4, respectively. Tetraethylammonium uptake was pH-dependent, and overshoot uptake was observed in the presence of an outwardly directed proton gradient. A protonophore and membrane potential affected the overshoot uptake. Furthermore, preloading tetraethylammonium in the vesicles significantly increased the rate of uptake of [14C]tetraethylammonium. In mouse kidney, OCTN1 was expressed predominantly at the apical membrane of cortical proximal tubular epithelial cells. It was concluded that OCTN1 is involved in renal excretion of organic cations across the apical membrane in a pH-dependent, membrane potential-sensitive manner and is affected significantly by the organic cations on the trans side, showing counter transport activity.

Sodium-lithium countertransport activity of red blood cells (SLC) in patients with essential hypertension (EH) and dyslipidaemia (D)

Sodium-lithium countertransport activity of red blood cells (SLC) in patients with essential hypertension (EH) and dyslipidaemia (D)

HbA1c levels and erythrocyte transport functions in complication-free type 1 diabetic children and adolescents.

Higher erythrocyte sodium-lithium countertransport activity (SLC) is implicated in the development of diabetic nephropathy. Altered glucose homeostasis and genetic susceptibility are claimed to play a role in the elevation of SLC. We aimed to test whether metabolic control or the genetic variants of G protein beta 3 (Gb3) subunits determine SLC and other erythrocyte transport activities in complication-free stage of type 1 diabetes. A total of 96 complication-free type 1 diabetic children and adolescents were enrolled. SLC, Na(+)/K(+)-ATPase (NAK) and Ca(2+)-ATPase (CA) were measured by functional assays in erythrocytes. Gb3-C825T polymorphism was determined by PCR-RFLP. Results were related to HbA(1c) and were compared to those of 97 healthy controls. SLC activity was higher in diabetics (387+/-146 vs. 280+/-65 mmol/RBC. hour) and correlated with HbA(1c) levels (y=0.004x+6.42, r=0.33, n=96, p<0.01). NAK and CA activities were unaltered. The prevalence of (825)T allele was similar in the patient and control groups (0.34 vs 0.37) and no differences in enzyme activities were observed between the (825)T allele-positive and negative subjects. Although metabolic control correlated with SLC, other membrane functions were not affected. Therefore we hypothesize that the relationship between advanced glycation and SLC elevation is not causative. Rather, a genetic susceptibility for the coexistence of poor metabolic control and higher SLC is more likely. However, the presence of Gb3-C825T variant is not likely to be a risk factor for SLC-elevation and altered metabolic control diabetes.

Sodium/lithium countertransport and intracellular calcium concentration in patients with essential hypertension and coronary heart disease

The present study was designed to test the hypothesis that enhanced intracellular calcium signalling and increased sodium/lithium countertransport (Na+/Li+ CT) activity may be associated with coronary heart disease (CHD) in non-diabetic patients with essential hypertension. Platelet-activating factor (PAF)-evoked rises in the intracellular calcium concentration ([Ca2+]i) were measured in Epstein–Barr-virus-immortalized lymphoblasts from 62 hypertensive patients with CHD and 34 patients without CHD. Na+/Li+ CT activity was assessed in erythrocytes from 80 hypertensive patients with CHD and 46 patients without CHD. Baseline values of unstimulated and PAF-stimulated [Ca2+]i were not significantly different between hypertensive subjects with (baseline, 126±5nmol/l; stimulated, 550±43nmol/l) and without (baseline, 125±5nmol/l; stimulated, 654±105nmol/l) CHD. Similarly, Na+/Li+ CT activity was not significantly different between the two groups (patients with CHD, 219±8µmol·l-1·h-1; patients without CHD, 234±10µmol·l-1·h-1). We conclude that intracellular signal transduction, as indicated by PAF-induced rises in [Ca2+]i and Na+/Li+ CT activity, is not associated with an increased risk of CHD in non-diabetic patients with essential hypertension.

3P-0720 Sodium-lithium countertransport activity of red blood cells (SLC) in patients with dyslipidaemia (D)

3P-0720 Sodium-lithium countertransport activity of red blood cells (SLC) in patients with dyslipidaemia (D)

Erythrocyte Sodium-Lithium Countertransport and Blood Pressure

Increased activity of erythrocyte sodium-lithium countertransport is associated with essential hypertension. Sodium-lithium countertransport is highly heritable, but no single gene product mediating the exchange or explaining the association of increased sodium-lithium countertransport activity and hypertension has been identified. We performed a linkage study by using erythrocyte sodium-lithium countertransport as a quantitative phenotype and genome-wide markers at an average resolution of approximately 10 cM to identify quantitative trait loci explaining sodium-lithium countertransport activity. A peak LOD score of 2.83 was detected on chromosome 15q at D15S642, a marker previously shown to be linked to blood pressure. Several genes mapped to this region are possible candidates for factors affecting erythrocyte sodium-lithium countertransport and/or blood pressure. Further studies confirming the presence of a quantitative trait locus in this region and evaluating these candidate genes may help explain the association of elevated sodium-lithium countertransport and hypertension.

The apolipoprotein E2 allele modulates activity and maximal velocity of the sodium–lithium countertransporter

Background Alterations in erythrocyte sodium–lithium countertransport (SLC) activity and its maximal velocity (V max) are associated with hypertension and hypertriglyceridemia. The presence of apolipoprotein (apo) E variants is associated with hypertriglyceridemia. This study investigated the relationship between apoE phenotype and SLC kinetics. Methods Cardiovascular risk factors and SLC kinetics were measured in 171 subjects and 69 controls. Apolipoprotein E phenotypes were determined by Western blotting. Results Patients were 51% male, aged 56 ± 13 years, with a blood pressure (BP) of 134 ± 22/81 ± 11 mm Hg, total cholesterol of 6.71 ± 1.57 (256 ± 61 mg/dL); median triglycerides 1.65 mmol/L (146 mg/dL) (range, 0.31 to 9.85 mmol/L; 27 to 872 mg/dL) and high-density lipoprotein (HDL) 1.39 ± 0.43 mmol/L (54 ± 16.6 mg/dL); fasting glucose 4.91 ± 0.61 mmol/L (88.5 ± 11.0 mg/dL); median insulin 11.7 IU/L (range, 3.7 to 39.8 IU/L). Phenotype frequencies were E3/E3 56%, E2/E3 14%, E2/E2 1%, E3/E4 27%, and E4/E4 2%. The SLC activity, V max, and sodium affinity (K m) were not significantly different with respect to apoE phenotype in simple analysis by Kruskal Wallis test. However, in multiple regression analysis after exclusion of BP, a strong co-correlate of SLC activity, the presence of an apoE2 allele was associated reduced activity (β = −0.061; P = .01) along with HDL:apoA1 ratio (β = −0.170; P < .001), whereas for the kinetic parameter V max, associations were found with triglyceride (β = 0.029; P = .04), HDL:apoA1 ratio (β = −0.186; P = .03) and the presence of an apoE2 allele (β = −0.089; P = .04). Conclusions These findings suggest that the apoE phenotype may modulate SLC activity and that the presence of an apoE2 allele phenotype is associated with lower SLC activity and V max.

Increased red cell sodium-lithium countertransport and lymphocyte cytosolic calcium are separate phenotypes in patients with essential hypertension.

Increased red blood cell sodium-lithium countertransport (SLC) activity and elevated intracellular calcium have been observed in hypertensive patients. The association of these ion transport abnormalities with each other and with another phenotype, insulin resistance, has been suggested. We investigated whether elevated SLC activity and increased lymphocyte cytosolic calcium (Ca(cyt)) occur in the same individuals and whether either is associated with hyperinsulinaemia. We measured SLC activity, lymphocyte Ca(cyt)and fasting insulin levels in hypertensive patients and normal subjects. Consistent with prior studies, SLC activity was significantly and positively correlated with fasting insulin levels (r = 0.45, P < 0.01). However, SLC activity and lymphocyte Ca(cyt) were significantly but inversely correlated (r = -0.42, P < 0.01) and lymphocyte Ca(cyt) was also inversely correlated with fasting insulin (r = -0.55, P < 0.001). When the study participants were instead separated into two groups based on fasting insulin levels, those above the median (15 microU/ml) had significantly higher SLC activity and significantly lower Ca(cyt). When separated by lymphocyte Ca(cyt) levels (above or below 120 nM) those patients with low lymphocyte Ca(cyt) had significantly higher SLC activity and significantly higher insulin levels. Multiple linear regression showed that fasting insulin was significantly predictive of SLC activity (P = 0.05) and Ca(cyt) (P < 0.01). Thus, elevated SLC activity and increased lymphocyte Ca(cyt) are separate and distinct ion transport phenotypes in hypertensive patients, linked through a relationship to hyperinsulinaemia that is direct with SLC activity and inverse with lymphocyte Ca(cyt).

Sodium-lithium countertransport activity in proximal tubule cells

Sodium-lithium countertransport activity in proximal tubule cells

Sodium-lithium countertransport is increased in normoalbuminuric type 1 diabetes but is not related to other risk factors for microangiopathy.

It has been reported that sodium-lithium countertransport (Na/Li CT) activity is increased in patients with diabetes mellitus and that this increased Na/Li CT activity is associated with the development of diabetic nephropathy. It is unclear however, whether Na/Li CT is related to other pathophysiological factors in diabetic patients. We studied kinetic parameters of Na/Li CT activity together with other putative risk factors for microangiopathy in normoalbuminuric type 1 diabetic patients and matched control subjects. We measured maximum velocity (Vmax) and sodium affinity (Km) of Na/Li CT in 53 diabetic patients and 45 healthy controls. Endothelial function was assessed by monitoring forearm vascular response to intrabrachial infusion of acetylcholine. Blood samples were collected for measurement of HbA1c, glucose, insulin and lipids. Blood pressure was measured intra-arterially. Renal haemodynamics were measured by inulin/p-aminohippurate clearance. Urinary albumin was measured by enzyme-linked immunosorbent assay. Transcapillary escape of albumin (TERalb) was calculated by the disappearance curve of 125I-labelled albumin. Vmax was increased in diabetic patients (779 +/- 36 micromol Li+ h-1 L-1 erythrocytes vs. 623 +/- 35 in controls, P < 0.01), whereas Km was decreased (64 +/- 16 mmol L-1 vs. 76 +/- 27 in controls, P = 0.03). The ratio of Vmax : Km was 12.4 +/- 0.6 in diabetic patients and 8.9 +/- 0.9 in controls (P < 0.001). When comparing diabetic patients in the lowest and highest quartile of Vmax or Km there were no differences in blood pressure, renal haemodynamics, urinary albumin excretion, TERalb, endothelial function, HbA1c, glucose, insulin, or lipid profile. Na/Li CT is increased in uncomplicated type 1 diabetes and characterized by an increase in Vmax and a decrease in Km. The increase in Na/Li CT is not associated with changes in endothelial function, degree of metabolic control, blood pressure or renal haemodynamics.

Sodium-Lithium Countertransport Activity Is Linked to Chromosome 5 in Baboons

Sodium-Lithium Countertransport Activity Is Linked to Chromosome 5 in Baboons

Sodium-lithium countertransport activity is linked to chromosome 5 in baboons.

The genes involved in the regulation of cellular sodium transport characteristics, which are correlated with some forms of essential hypertension, have not yet been identified. We are studying the genes and environmental factors that affect red blood cell sodium-lithium countertransport (SLC) activity and intracellular sodium (ICNa) concentration in 634 baboons that comprise 11 pedigrees of 2 and 3 generations each. To detect and locate possible quantitative trait loci (QTLs) that affect SLC activity and ICNa concentration, we performed a genome screen by using a maximum likelihood-based variance-components linkage analysis program (SOLAR). SLC and ICNa phenotypes as well as genotypes on 281 microsatellite loci were available for all pedigreed animals. Both SLC and ICNa traits were highly heritable (residual heritability 0.593+/-0.083 [P<0.0001] and 0.739+/-0.082 [P<0.0001], respectively). We obtained evidence that a possible QTL for SLC activity is located on the baboon homologue of human chromosome 4 between D4S2456 and D4S2365 with a maximum multipoint lod score of 9.3 (P<10(-)(10)) near D4S1645. This QTL accounts for approximately two thirds of the total additive genetic variation in SLC activity in baboons. Although ICNa concentration was highly heritable, we found no evidence for linkage to a QTL with use of this methodology. Thus, we have evidence that a gene located on the baboon homologue of human chromosome 4 (baboon chromosome 5) affects cell sodium transport in baboons.

The Role of Intracellular Signalling Mechanisms on Erythrocyte Sodium — Lithium Countertransport Activity

The Role of Intracellular Signalling Mechanisms on Erythrocyte Sodium — Lithium Countertransport Activity

Elevated Na+/Li+ Countertransport and Cytosolic Ca2+ Represent Separate and Distinct Phenotypes in Essential Hypertension

P124 Attempts to understand the pathogenesis of essential hypertension have focused on identifying intermediate phenotypes such as defects in cation metabolism. Elevated red blood cell sodium-lithium countertransport (SLC) activity is frequently present in hypertensive patients. Cytosolic calcium (Ca cyt ) is also elevated in blood cells from hypertensive patients. However, despite their frequent occurrence in hypertensive patients, these two markers of cation homeostasis have not been simultaneously investigated in the same individuals. We studied lymphocyte Ca cyt and red cell SLC activity in hypertensive (n = 43) and normal subjects (n = 22) to determine whether elevated SLC activity and lymphocyte Ca cyt occur in the same individuals. Red cell SLC and lymphocyte Ca cyt were significantly ( P vs. normotensives. However, SLC activity and Ca cyt were significantly but inversely correlated (r=-0.42, P cyt (84 ± 5 nM) had elevated SLC (0.41 ± 0.03 mmol/L cell x h, P cyt (188 ± 15) had lower SLC (0.32 ± 0.03 mmol/L cell x h, P P cyt was inversely correlated with fasting insulin (r=-0.55, P P vs . 0.28 ± 0.02 mmol/L cell x h) and significantly ( P =0.017) lower Ca cyt (177 ± 18 vs. 105 ± 8 nM). Thus, elevated SLC activity and elevated lymphocyte Ca cyt are separate and distinct ion transport phenotypes in hypertensive patients, but they are linked through a relationship to hyperinsulinemia that is direct with SLC and inverse with lymphocyte Ca cyt .

Elevated Na + /Li + Countertransport and Cytosolic Ca 2+ Represent Separate and Distinct Phenotypes in Essential Hypertension

P124 Attempts to understand the pathogenesis of essential hypertension have focused on identifying intermediate phenotypes such as defects in cation metabolism. Elevated red blood cell sodium-lithium countertransport (SLC) activity is frequently present in hypertensive patients. Cytosolic calcium (Ca cyt ) is also elevated in blood cells from hypertensive patients. However, despite their frequent occurrence in hypertensive patients, these two markers of cation homeostasis have not been simultaneously investigated in the same individuals. We studied lymphocyte Ca cyt and red cell SLC activity in hypertensive (n = 43) and normal subjects (n = 22) to determine whether elevated SLC activity and lymphocyte Ca cyt occur in the same individuals. Red cell SLC and lymphocyte Ca cyt were significantly ( P &lt;0.01) higher in the hypertensive patients vs. normotensives. However, SLC activity and Ca cyt were significantly but inversely correlated (r=-0.42, P &lt;0.01). Patients with low Ca cyt (84 ± 5 nM) had elevated SLC (0.41 ± 0.03 mmol/L cell x h, P&lt; 0.05) whereas those with elevated Ca cyt (188 ± 15) had lower SLC (0.32 ± 0.03 mmol/L cell x h, P&lt; 0.05). We then compared both phenotypes to a separate intermediate phenotype, fasting insulin. SLC and fasting insulin levels were significantly and positively correlated (r=0.45, P &lt;0.01), consistent with prior studies showing elevated SLC activity in the setting of hyperinsulinemia. Ca cyt was inversely correlated with fasting insulin (r=-0.55, P &lt;0.001). Individuals with insulin levels above the median (15 mU/ml) had significantly ( P &lt;0.01) higher SLC activity (0.43 ± 0.03 vs . 0.28 ± 0.02 mmol/L cell x h) and significantly ( P =0.017) lower Ca cyt (177 ± 18 vs. 105 ± 8 nM). Thus, elevated SLC activity and elevated lymphocyte Ca cyt are separate and distinct ion transport phenotypes in hypertensive patients, but they are linked through a relationship to hyperinsulinemia that is direct with SLC and inverse with lymphocyte Ca cyt .

Genetic variation in the beta-3-adrenergic receptor in essential hypertension

We investigated the role of the beta-3-adrenergic receptor polymorphism in membrane lipid composition and erythrocyte membrane sodium transport in essential hypertensive patients. We studied 87 essential hypertensive patients determining: The Trp64Arg mutation of the beta-3-adrenergic receptor by PCR, lipoprotein profile by standard laboratory methods, membrane lipid composition by IATROSCAN and erythrocyte sodium lithium countertransport by Canessa technique. Patients with the mutation as compared with those without it showed lower membrane cholesterol, membrane cholesterol phospholipids ratio and erythrocyte sodium lithium countertransport, however blood pressure and the other studied variables were similar in both groups of patients. After adjusting by sex sodium lithium countertransport activity remained significant. These data suggest that although the Trp64Arg mutation of the beta-3-adrenergic receptor is related with a different membrane lipid composition and erythrocyte sodium lithium countertransport values it does not contribute to blood pressure levels in essential hypertensive patients.

Erythrocyte Na+/Li+ countertransport and Na+/K+‒2Cl− co-transport in essential hypertension

Correspondence| August 24 1999 Erythrocyte Na+/Li+ countertransport and Na+/K+ -2Cl- co-transport in essential hypertension T Hardman; T Hardman Search for other works by this author on: This Site PubMed Google Scholar R H Clifford; R H Clifford Search for other works by this author on: This Site PubMed Google Scholar A S Wierzbicki A S Wierzbicki Search for other works by this author on: This Site PubMed Google Scholar Clin Sci (Lond) (1999) 97 (3): 339–340. https://doi.org/10.1042/cs0970339 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation T Hardman, R H Clifford, A S Wierzbicki; Erythrocyte Na+/Li+ countertransport and Na+/K+ -2Cl- co-transport in essential hypertension. Clin Sci (Lond) 1 September 1999; 97 (3): 339–340. doi: https://doi.org/10.1042/cs0970339 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsClinical Science Search Advanced Search This content is only available as a PDF. The Biochemical Society and the Medical Research Society © 19991999 Article PDF first page preview Close Modal You do not currently have access to this content.

Decreased activity of the red blood cell ATPase-dependent Na+ pump in patients with cardiac syndrome X.

Marked Na(+)/Li(+) countertransport hyperactivity and post-load hyperinsulinaemia have been described in 93% of patients with cardiac syndrome X. We hypothesized that more complex abnormalities in Na(+) traffic across the cell membrane are present in these patients. The aim of the present study was to evaluate the activities of the two main transporters responsible for transmembrane Na(+) transport, i.e. the ATPase-dependent Na(+) pump and the Na(+)-K(+)-2Cl(-) co-transporter, in a selected group of patients with cardiac syndrome X. We evaluated 19 patients with cardiac syndrome X and 14 control subjects. The ATPase-dependent Na(+) pump and Na(+)-K(+)-2Cl(-) co-transport activities were assessed from Na(+)-loaded red blood cells by using nystatine, in the presence of furosemide and ouabain, as appropriate. Erythrocyte Na(+)/Li(+) countertransport activity, serum lipid and post-load (75 g of oral glucose) insulin levels were also evaluated. The V(max) of Na(+)/Li(+) countertransport (P=0.0001) and post-load insulin levels (120 min; P=0.001) were confirmed to be higher in patients with syndrome X than in controls. The V(max) of Na(+)-K(+)-2Cl(-) co-transport was similar in patients and controls. By contrast, the V(max) of the ATPase-dependent Na(+) pump was significantly lower (P=0.002) in syndrome X patients (3.13+/-0.87 mmol.h(-1).l(-1)) than in controls (4.28+/-1.10 mmol.h(-1).l(-1)). Serum total cholesterol and triacylglycerol concentrations were also higher in patients with syndrome X than in control subjects (P<0.0001). Thus decreased activity of the ATPase-dependent Na(+) pump was present in patients with cardiac syndrome X. Such an abnormality has the biological potential to augment microvascular tone and the response to constrictor stimuli via increased intracellular free Ca(2+). Of note, syndrome X patients also manifested Na(+)/Li(+) countertransport hyperactivity which, in turn, is known to induce peripheral insulin resistance and consequent abnormalities in insulin secretion and lipid turnover. Thus cardiac syndrome X appears as a multifaceted syndrome presenting with either metabolic or cardiovascular symptoms, or both, based on the expression of complex abnormalities in Na(+) traffic across the cell membrane.