Elevation of red cell sodium-lithium countertransport in hyperlipidemias

Sodium-lithium countertransport activity in healthy, dyslipidemic, and hypertensive individuals

The aim of our study was to investigate the role of dyslipidemia on red blood cell sodium-lithium countertransport activity in healthy and hypertensive individuals. A total of 128 Caucasian individuals, aged 20 to 60 years old, were divided into 4 groups: dyslipidemic/ hypertensive, dyslipidemic/normotensive, normolipidemic/hypertensive, and normolipidemic/ normotensive (controls). Sodium-lithium countertransport activity was determined based on the Canessa et al method. Sodium-lithium countertransport activity was significantly higher in all patient groups compared with controls (P < .001) and similar in the 3 patient groups. Sodium-lithium countertransport activity was significantly and positively associated with triglyceride levels (P < .001), body mass index (P < .001), total cholesterol levels (P = .001), and systolic (P = .001) and diastolic blood pressure (P = .001). In multivariate regression analysis, triglycerides made the largest contribution to sodium-lithium countertransport variation among the variables tested (R(2) = 0.273). Our results suggest that dyslipidemia affects sodium-lithium countertransport activity independently of essential hypertension and even to a greater extent than hypertension.

Effects of atorvastatin on red-blood cell Na(+)/Li(+) countertransport in hyperlipidemic patients with and without hypertension

BACKGROUND

To explore the effect of short-term cholesterol-lowering treatment with atorvastatin on erythrocyte sodium-lithium countertransport (Na(+)/Li(+) CT) activity.

METHODS

Group A consisted of 30 patients (14 men) with mild essential hypertension (systolic blood pressure (SBP), 140-159 mm Hg and/or diastolic BP, 90-99 mm Hg) and primary hypercholesterolemia low-density lipoprotein (LDL) cholesterol >4.1 mmol/l and triglycerides (TG) <2.8 mmol/l), group B of 30 normotensive patients (16 men) with primary hypercholesterolemia, while 37 (18 men) healthy volunteers comprised the control group. After a 6-week dietary lead-in, all eligible patients were prescribed 20 mg/day of atorvastatin. Anthropometric data, blood-pressure (BP) measurements and determinations of lipid, non-lipid metabolic parameters (including homeostasis model assessment index, (HOMA-IR)) and erythrocyte Na(+)/Li(+) CT activity were collected at baseline and after 12 weeks of treatment.

RESULTS

At baseline Na(+)/Li(+) CT activity was significantly higher in group A and B compared with the control group and correlated directly with obesity indices, systolic and diastolic BP, total cholesterol, LDL-cholesterol, TG, apolipoprotein B (apoB), HOMA-IR, uric acid and inversely with high-density lipoprotein (HDL)-cholesterol and apoA1. Systolic and diastolic BP levels, HOMA-IR and Na(+)/Li(+) CT activity were significantly decreased after atorvastatin treatment in both patient groups. The reduction in Na(+)/Li(+) CT activity correlated with baseline Na(+)/Li(+) CT activity and the changes in HOMA-IR values.

CONCLUSIONS

Short-term treatment with atorvastatin for patients with hypercholesterolemia, and with or without essential hypertension, is associated with a significant reduction in the erythrocyte Na(+)/Li(+) CT activity, BP levels and insulin resistance independent of concomitant changes in lipid parameters.

Fibroblast Na+-Li+ countertransport rate is elevated in essential hypertension

OBJECTIVES

Elevated erythrocyte Na+- Li+ countertransport (SLC) rates are commonly found in essential hypertension. We have recently shown that human skin fibroblasts functionally express a phloretin-sensitive Na+-H+ exchange (NHE) which may also be similar to erythrocyte SLC because of amiloride-insensitivity.

DESIGN AND METHODS

We investigated whether elevations in fibroblast SLC parallel the known elevations in erythrocyte SLC and in cell NHE that characterize essential hypertension.

RESULTS

Higher fibroblast SLC rates were found among hypertensive patients (n = 23, median 48.8 nmol Li+/ mg(protein) per min) than in 19 normotensive individuals of similar age and sex (median 14.8 nmol Li+/mg(protein) per min, P= 0.0002). As expected, erythrocyte SLC was elevated in patients with hypertension (median 411 versus 329 micromol/l(cell) per h, P= 0.0273), but was not quantitatively related to fibroblast SLC. Finally, fibroblast NHE exchange activity was higher in essential hypertension (median Vmax 14.2 versus 7.6 mmol H+/l(cell) per min, P= 0.002), but was unrelated to fibroblast SLC.

CONCLUSIONS

These findings extend to human skin fibroblasts the notion of abnormal Li+ transport in essential hypertension, and appear to be in accordance with the hypothesis that fibroblast SLC may be independent of NHE. However, molecular studies will be required to understand whether distinct exchangers and/or regulation mechanisms underlie these dysregulations.

Gordon's syndrome: increased maximal rate of the Na-K-Cl cotransport and erythrocyte membrane replacement of sphingomyelin by phosphatidylethanolamine

OBJECTIVE

Gordon's syndrome comprises hypertension, hyperchloremic acidemia, hyperkalemia and intact renal function. We hypothesize that disturbances of one or more cell membrane ion carriers, handling sodium, chloride and potassium, might be relevant in this disorder and, furthermore, that such disturbances might be related to altered.cell membrane composition.

DESIGN AND METHODS

In a patient diagnosed with Gordon's syndrome, we assessed the kinetics (K(m) and maximal rate) of four membrane sodium transport systems in sodium-enriched erythrocytes, according to the technique of Garay. We also measured the lipid composition of erythrocyte membrane in this patient and 69 essential hypertensive controls, using the latroscan technique.

RESULTS

Compared to reference values of patients with essential hypertension, this patient exhibited a marked increase in the maximal rate of the Na+-K+-2Cl(-)-cotransport (964.0 micromol/l per cell versus the 391.6 +/- 222 micromol/l per cell in essential hypertensives). Also, there was an increased concentration of erythrocyte membrane phosphatidylethanolamine and a reduced concentration of sphingomyelin (27.9 and 11.1% versus 17.9 +/- 3.8% and 18.2 +/- 3.4%, respectively).

CONCLUSIONS

We conclude that this abnormality in membrane Na+-K+-2Cl- cotransport could be responsible for the hyperkalemia, hyperchloremic acidemia and increased reabsorption of sodium observed in this condition and, furthermore, that such disturbance in membrane cotransport might be related to altered phospholipid concentration in cell membranes.

Effects of fluvastatin treatment on red blood cell Na+ transport systems in hypercholesterolemic subjects

This study was performed to ascertain the effects of short-term cholesterol-lowering therapy with fluvastatin on red blood cells Na+ transport systems. Forty familial hypercholesterolemic subjects (FH; 19 men and 21 women) without hypertension or cardiovascular disease were given a placebo for 4 weeks, and then randomized in two groups. Twenty (fluvastatin group) were given fluvastatin (40 mg/day), and the other 20 (placebo group) continued placebo administration. After the placebo period and after 4 and 12 weeks of placebo or fluvastatin treatment, we measured Na+/K+ pump activity, Na+/K+ cotransport (Na+/K+ Ct), Na+/Li+ countertransport (Na+/Li+ Cnt), passive Na+ permeability (Na+PP), and internal Na+ content (Na+i). The same parameters were measured in 23 control subjects (C) with normal cholesterolemic values, who were matched for sex and age. FH had higher Na+/Li+ Cnt values than C (193.2 +/- 59.4 vs. 139.8 +/- 48.7 microM cells/h; p < 0.01), an increase in Na(+)PP (0.034 +/- 0.012/h vs. 0.018 +/- 0.004/h; p < 0.001), and higher Na(+)i (7.5 +/- 1.5 vs. 6.2 +/- 0.9 mM cells; p < 0.001). In hypercholesterolemic subjects, Na(+)i values were correlated with cholesterol (total and LDL) and apo B levels, whereas an inverse correlation was found for HDL-c and apo AI levels. Reduced total and LDL cholesterol and apo B levels after fluvastatin treatment caused a decrease in both Na(+)/Li(+) Cnt (from 186.1 +/- 60.5 to 125.1 +/- 34.0 microM cells/h; p < 0.001) and Na(+) PP (from 0.035 +/- 0.013/h to 0.02 +/- 0.016/h; p < 0.01), and an increase in Na+/K+ pump activity (from 1,549.0 +/- 507.7 to 1,894.2 +/- 536.2 microM cells/h; p < 0.04), with a significant reduction in the internal Na+ content (from 7.5 +/- 1.6 to 5.8 +/- 2.4 mM cells; p < 0.001). Our findings show that hypercholesterolemia affects red blood cell Na+ transport systems, with an increase in Na+/Li+Cnt, Na+PP, and the internal Na+ content. Cholesterol-lowering treatment with fluvastatin influences Na+ transport systems and reduces the internal Na+ content. This might also be responsible for the greater vascular reactivity observed in hypercholesterolemic patients, and its amelioration after a reduction in cholesterol levels.

Sibling resemblance of erythrocyte ion transporters in French-Canadian sibling-pairs affected with essential hypertension

OBJECTIVES

Erythrocyte Na+/Li+ countertransport and Na+,K+ cotransport are increased in some Caucasians with essential hypertension. This study examines the relative contributions of genetic and shared environmental factors to the activity of these ion carriers in French-Canadian sibling-pairs affected with essential hypertension.

DESIGN

The activity of Na+/Li+ countertransport and Na+,K+ cotransport (rate of Na+ o-dependent Li+ efflux and bumetanide-sensitive 86Rb influx, respectively) was measured in 122 French-Canadian siblings with essential hypertension, including 36 brother/brother and 48 sister/sister pairs. Sibling/sibling correlations were estimated using the FCOR program of the S.A.G.E. package.

RESULTS

Na+/Li+ countertransport and Na+,K+ cotransport were respectively higher by 27% (P = 0.002) and 42% (P = 0.0009) in erythrocytes from men compared with women. Intra-individual correlation analysis did not reveal a significant effect of age on the activity of these ion transporters in both males and females, and an influence of plasma lipids (triglycerides, cholesterol, low-density lipoprotein, high-density lipoprotein) in females. In males, Na+,K+ cotransport was correlated with the level of serum triglycerides only (P = 0.01). Familial correlation analysis showed that sibling resemblance of Na+/Li+ countertransport and Na+,K+ cotransport was higher in men (r = 0.26 and 0.39) than in women (r = 0.01 and 0.03, respectively).

CONCLUSION

The present data indicate that different factors contribute to the regulation of monovalent ion carriers in erythrocytes from Caucasian men and women with essential hypertension. The activity of erythrocyte Na+/Li+ countertransport and Na+,K+ cotransport appears to be more strongly determined by inheritable factors in men than in women.

Prospective analysis of traits related to 6-year change in sodium-lithium countertransport. Gubbio Population Study Research Group

Sodium-lithium countertransport (Na-Li CT) activity in red blood cells relates cross-sectionally and longitudinally to blood pressure and hypertension. Lifestyle and metabolic factors relate cross-sectionally to this sodium transporter. The aim of this study was to conduct a prospective analysis of 6-year Na-Li CT change and of traits related to Na-Li CT change. In 2183 participants in the Gubbio Population Study (972 men and 1211 women; baseline ages, 18 to 74 years), the following data collected at baseline and 6-year follow-up were analyzed: Na-Li CT; gender; age; body mass index (BMI); blood pressure; antihypertensive treatment; alcohol intake; smoking habits; urinary sodium-to-potassium ratio; and plasma cholesterol, glucose, uric acid, sodium, potassium, and triglycerides (measured only at follow-up). Six-year changes were defined as follow-up minus baseline values. Na-Li CT was higher at follow-up than at baseline in both genders (P<0.001). Baseline Na-Li CT; baseline and change values of BMI; and change values of alcohol intake, plasma potassium, and plasma glucose related to Na-Li CT change significantly and independently with control for other variables. Follow-up plasma triglyceride levels also related independently to Na-Li CT change. Coefficients were positive for BMI, alcohol intake, and plasma glucose and triglyceride levels and were negative for baseline Na-Li CT and plasma potassium levels. Baseline and change values of other variables did not relate significantly to Na-Li CT change. In conclusion, in prospective analyses, BMI, alcohol intake, plasma glucose, and lipids were directly related to Na-Li CT change; baseline Na-Li CT and plasma potassium levels were inversely related. The data support the concept that lifestyle and related metabolic factors influence Na-Li CT.

No linkage of the lipoprotein lipase locus to hypertension in Caucasians

OBJECTIVE

A previous study has shown significant linkage of five markers near the lipoprotein lipase locus to systolic blood pressure, but not to diastolic blood pressure, in nondiabetic members of 48 Taiwanese families selected for noninsulin-dependent diabetes. However, lipoprotein lipase markers did not appear strongly linked to systolic blood pressure in a study of Mexican-Americans using a variety of selection schemes. The objective of the current study was to test whether markers near the lipoprotein lipase gene were linked to hypertension in Caucasians.

DESIGN

To test for linkage of genetic markers in or near the lipoprotein lipase gene to hypertension in Caucasians, two sets of Caucasian hypertensive sibships were genotyped. The samples included 261 sibships (431 effective sibpairs) from four field centers of the National Heart, Lung and Blood Institute Family Heart Study and 211 sibships (282 effective sibpairs) from the Health Family Tree database in Utah.

RESULTS

Two highly polymorphic markers in or near the lipoprotein lipase gene showed no evidence of excess allele sharing in either set of hypertensive sibships. Combining the two datasets resulted in 653 and 713 effective sibpairs for the two markers, sharing 0.495 +/- 0.30 and 0.486 +/- 0.28 alleles identical by descent compared to an expected sharing of 0.50. Multipoint analysis of the two loci also did not show linkage (P = 0.95).

CONCLUSIONS

We conclude that the lipoprotein lipase locus and nearby regions do not appear to be linked to hypertension in Caucasians.

Na-Li countertransport kinetics in the relatives of hypertensive patients with abnormal Na-Li countertransport activity

Familial factors are believed to be important in determining the high sodium-lithium countertransport activity (defined as >0.40 mmol Li/(h x l cell) at external sodium concentration of 140 mmol/L (Nae 140)) which is observed in a proportion of patients with essential hypertension. However, environmental factors such as pregnancy and dyslipidemia also affect activity. High sodium-lithium countertransport activity (Nae 140) in essential hypertension is mainly due to a low Michaelis constant (Km) and is associated with a high Vmax/Km ratio. In contrast, dyslipidemias affect Vmax. This study aimed to determine if there was evidence that Km and Vmax/Km ratios are influenced by familial factors. Sodium-lithium countertransport kinetics were measured in the 47 first degree relatives of 12 hypertensive probands with abnormal sodium-lithium countertransport kinetics and 35 normotensive control subjects. Sodium-lithium countertransport was measured as Na-stimulated Li efflux from lithium loaded erythrocytes. The relatives had significantly reduced Km and increased Vmax/Km compared to normal subjects. Eleven relatives had high sodium-lithium countertransport activity (Nae 140), associated with low Km and high Vmax/Km. The 14 relatives that were hypertensive had abnormalities of sodium-lithium countertransport kinetics. The results of this study suggest that familial factors are important in determining the Km and Vmax/Km of sodium-lithium countertransport activity. Studies aimed at determining the inheritance of sodium-lithium countertransport and its use as an intermediate phenotype of essential hypertension must measure its kinetic determinants to reduce the risk of confounding effects from other variables.

Plasma triglycerides and red cell ion transport alterations in genetically hypertensive rats

Ion transport abnormalities in essential hypertension are often associated with concomitant changes of lipid metabolism, but this information is missing in rats with genetic hypertension. We therefore studied the alterations of red cell Na+ and K+ transport and their relationship to blood pressure and plasma lipids (cholesterol and triglycerides) in Prague hereditary hypertriglyceridemic (HTG) rats, Lyon hypertensive (LH) rats, and HTG x Lewis F2 hybrids. In both hypertensive models and F2 hybrids, red cell Na+ content (Na+(i)) was positively related to plasma triglycerides but not to plasma cholesterol levels. Na+(i) elevation was more pronounced in HTG than in LH rats, probably due to higher plasma triglycerides in the former strain. The two hypertensive strains differed in bumetanide-sensitive Na+ transport, which was augmented in HTG rats with low plasma cholesterol but suppressed in LH rats characterized by high cholesterol levels. In the two genetic models, there was a positive association of blood pressure with Na+ leak, and this was also confirmed by the cosegregation of these parameters in F2 hybrids. We conclude that the enhancement of Na+ leak represents the major ion transport abnormality in rats with genetic hypertension. The alterations in plasma lipids are important determinants of abnormal red cell ion transport in hypertensive models studied. Although the detailed mechanism of their participation in ion transport regulation is still not completely understood, triglyceride-dependent changes in membrane microviscosity seem to be responsible for the modulation of particular ion transport pathways.

Effect of dietary versus pharmacological correction of hypertriglyceridemia on red blood cell membrane sodium/lithium countertransport activity

An elevated red blood cell Na/Li countertransport (Na/Li CT) is often associated with high blood pressure and metabolic abnormalities. Recent studies suggested that a reduction in serum TG levels is associated with a decrease in Na/Li CT activity. However, it is still unclear if this phenomenon could be originated from systemic metabolic alterations or from modifications of the membrane dynamic properties. Aim of the present study was to investigate whether dietary or pharmacological TG lowering therapy might have a different effect on Na/Li CT activity and related metabolic parameters. Twenty normotensive hyper-TG patients were recruited from the Lipid outpatient Clinic: they had a baseline Na/Li CT activity significantly higher compared with age- and BMI-matched normolipidemic controls (386+/-33 vs 274+/-39 umol/l RBC/h, p<0.05). The patients were randomly prescribed one of the following two-months treatment: Group 1)-triglyceride lowering diet; Group 2)-lipid lowering drug (Gemfibrozil 600 mg b.i.d.). Na/Li CT and metabolic and anthropometric variables were measured at baseline and after 1 and 2 months of treatment. At the end of intervention, there was in both groups a significant and comparable fall in plasma triglyceride (group 1: -2.61+/-0.73 mmol/l p<0.01; group 2: -4.29+/-1.20 mmol/l p<0.01). In the diet-treated group there were, in addition small but significant reductions in body weight (-3.7+/-0.8 kg p<0.01), fasting glucose (-0.36+/-0.14 mmol/l p<0.05) and insulin levels (-2.1+/-0.5 mU/l, p<0.01), while no such changes were observed in the fibrate treated patients. Na/Li CT activity was significantly and comparably reduced at the end of treatment in both groups (group 1: -97+/-28 umol/l cell/h, p<0.01; group 2: -89+/-30 umol/l cell/h, p<0.01). In conclusion, these results indicate that the decrease in Na/Li CT associated with both dietary and drug treatment of hypertriglyceridemia is to be traced to a direct effect of plasma TG concentration on this transport system (probably as a result of modification in the membrane lipid environment) rather than to changes in plasma insulin levels or insulin resistance.

A study of the temporal effect of alcohol on human erythrocyte sodium-lithium countertransport in relation to membrane cholesterol and phospholipids

The effect of a single dose of alcohol (0.8 g/kg), given with "diet coke," on erythrocyte sodium-lithium countertransport (SLC) in relation to membrane cholesterol and phospholipids was assessed over 24 h in 10 healthy volunteers. Baseline passive lithium efflux (0.168 +/- 0.008 mmol l-1 Cell H-1) was increased 1 h (0.202 +/- 0.014 mmol l-1 cell h-1; p < 0.030), and 4 h (0.200 +/- 0.014 mmol l-1 cell h-1; p < 0.020), but similar to that at 24 h postalcohol (0.173 +/- 0.011 mmol l-1 cell h-1). These changes were not associated with any change in intracellular lithium. Control SLC VMAX of 0.387 +/- 0.054 mmol l-1 cell h-1 fell at 1 h (0.328 +/- 0.050 mmol l-1 cell h-1; p = 0.0012) and 4 h (0.312 +/- 0.048 mmol l-1 cell h-1; p < 0.0005). Its value 24 h postalcohol (0.371 +/- 0.047 mmol l-1 cell h-1) was comparable to that at baseline. There was no significant change in the affinity of the transporter for external sodium throughout the experimental period, suggesting that the reduction in VMAX 1 and 4 h after alcohol ingestion resulted from a noncompetitive inhibition. Intracellular sodium 4 h after alcohol was lower than at baseline, but returned to the control value within 24 h. In a control group (n = 5), pretreatment with "diet coke" alone did not alter any of the measured parameters. It is concluded that alcohol pretreatment increases passive lithium efflux and decreases SLC Vmax. Both effects are evident up to at least 4 h postdosing, but recover within 24 h in the absence of further alcohol intake.

Cellular sodium membrane transport and cardiovascular risk factors in non-insulin-dependent diabetes mellitus

Association have been described between cardiovascular risk factors and abnormalities of both sodium-lithium countertransport (SLC) and sodium-hydrogen ion exchange in subjects with insulin-dependent diabetes mellitus. The data in subjects with non-insulin-dependent diabetes mellitus (NIDDM) are few and more conflicting. This investigation examines erythrocyte SLC rates and platelet sodium-hydrogen ion-exchange kinetics and their relationship to cardiovascular risk factors in 45 nondiabetic and 35 NIDDM white men. The two groups did not differ significantly in erythrocyte SLC or platelet buffering capacity, sodium-hydrogen ion-exchange maximal rate (Vmax), or Km for extracellular sodium. Within the whole group, controlling for the presence of diabetes, SLC correlated weakly with triglyceride concentration (r = .23, P = .05), but not with urinary albumin excretion rate (AER), systolic or diastolic blood pressure, body mass index (BMI), or concentrations of glucose, insulin, or total or high-density lipoprotein (HDL) cholesterol. Platelet sodium-hydrogen exchange was not significantly related to any cardiovascular risk factor studied. In conclusion, (1)SLC activity was not increased in NIDDM subjects; (2) SLC rates correlated weakly with serum triglyceride concentrations; (3) platelet sodium-hydrogen exchange Vmax and K(m) for extracellular sodium and platelet buffering capacity did not differ between diabetic and nondiabetic groups; and (4) there was no significant relationship between platelet Na+/H(+)-exchange kinetics and any of the cardiovascular risk factors studied.

Correlations of Na+-Li+ exchange activity with Na+ and Li+ binding and phospholipid composition in erythrocyte membranes of white hypertensive and normotensive individuals: a nuclear magnetic resonance investigation

Enhanced Na+-Li+ exchange activity has been reported in red blood cells (RBCs) of white patients with essential hypertension compared with RBCs of normotensive individuals. To understand the factors responsible for this finding, we applied novel and conventional spectroscopic and kinetic methods to blood samples from 10 hypertensive and 10 normotensive individuals. We measured the kinetic parameters (V std, V max, and K m) for RBC Na+-Li+ exchange by atomic absorption spectrophotometry and used 23Na and 7Li nuclear magnetic resonance relaxation methods to measure Na+ and Li+ binding to RBC membranes as well as 31P nuclear magnetic resonance spectroscopy to measure membrane phospholipid compositions. We found significant differences between the two groups for the affinity of Na+ for the RBC membrane (0.202 +/- 0.054 mmol/L-1 for hypertensive patients versus 0.296 +/- 0.071 mmol/L-1 for normotensive subjects, P<.005). The kinetic parameters of RBC Na+-Li+ exchange (V std, V max, and K m) were 0.32 +/- 0.09 and 0.66 +/- 0.17 mmol Li+/L cell.h and 160 +/- 62 mmol/L, respectively, for hypertensive patients versus 0.21 +/- 0.06 and 0.32 +/- 0.14 mmol Li+/L cell.h and 86 +/- 69 mmol/L for normotensive subjects (P<.05). The fractions of phosphatidylserine and phosphatidylethanolamine were 0.153 +/- 0.009 and 0.294 +/- 0.016 for hypertensive patients versus 0.138 +/- 0.013 and 0.325 +/- 0.018 for normotensive subjects (P<.05). The Na+ binding constants were negatively correlated with the Km values for both the hypertensive (r=-.61, P=.01) and normotensive (r=-.43, P=.04) groups. Changes in lipid-protein interactions in the RBC membranes of hypertensive patients appear to be responsible for weaker Na+ binding to the membrane and for the faster rates of RBC Na+-Li+ exchange.

Effects of membrane incorporation of short-chain phospholipids on sodium pump function in human erthrocytes

Erythrocyte membrane incorporation of exogenous short-chain diacyl phosphatidylcholines (PC) has been quantified by gas chromatography of fatty acid methyl esters of extracted membrane lipids after incubation of cells with sonicated aqueous suspensions of PC. The PCs studied included didecanoyl PC (C10-PC), dilauroyl PC (C12-PC), dimyristoyl PC (C14-PC) and dipalmitoyl PC (C16-PC). PC incorporation of 10-15 mol% was achieved by incubation at 37 degrees C for 0.5-24 h. Control cells incubated in saline alone showed a progressive reduction in endogenous polyunsaturated acyl chain content. Incubation with C10-PC and C16-PC was associated with reductions in membrane cholesterol. Experiments were performed with mixtures of PC and cholesterol in order to minimise this effect. Short-chain PC incorporation was associated with increases in intracellular Na+ and reduced intracellular K+ concentrations. Sodium pump activity was measured as the ouabain-sensitive rate of 86Rb+ influx and was significantly reduced by all PCs tested; mean reductions were 13-30%. These results confirm that the sodium pump in situ is sensitive to lipid acyl chain composition.

Red blood cell cation transports in uraemic anaemia: evidence for an increased K/Cl co-transport activity. Effects of dialysis and erythropoietin treatment

This study examines the role of uraemia and the effect of different dialysis treatments on red cell cation transport. We evaluated the main cation transport systems in erythrocytes of non-dialysed end-stage renal disease (ESRD) subjects, of patients undergoing haemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD), as well as the changes induced by human recombinant erythropoietin (r-HuEPO) administration. In uraemic undialysed and dialysed patients, we observed an increase in K/Cl co-transport activity and in shrinkage-induced amiloride-sensitive (HMA-sensitive) Na efflux (Na/H exchange) and a decrease in Na/K pump and Na/K/Cl co-transport activity, while Na/Li exchange was increased only in dialysed patients. In uraemic erythrocytes, we showed for the first time an increased K/Cl co-transport activity, which was cell age independent. Generally, the different method of dialysis (CAPD or HD) did not modify the cation transport abnormalities observed. During the treatment with r-HuEPO, all the systems, with the exception of the Na/K pump and Na/K/Cl co-transport, increased their activities following the increase of circulating young red cells. The changes produced under r-HuEPO administration were transient and cation transports returned to the baseline values within 100 days of treatment, indicating a primary and prominent pathogenetic role of uraemia in modulating the red cell membrane cation transport activities.

Microalbuminuria and erythrocyte sodium-hydrogen exchange in essential hypertension

Microalbuminuria (urinary albumin excretion between 20 and 200 micrograms/min) and abnormalities of red blood cell sodium-hydrogen exchange coexist in essential hypertensive patients. To evaluate how the two phenomena relate, we recruited 10 untreated microalbuminuric male essential hypertensive patients without diabetes to be compared with an equal number of matched essential hypertensive patients excreting albumin in normal amounts as well as 10 healthy control subjects. Sodium-hydrogen exchange values were increased to a comparable extent in microalbuminuric and normoalbuminuric hypertensive patients. Systolic and mean blood pressures were higher in microalbuminuric patients. Fasting insulin was greater and high-density lipoprotein cholesterol lower in patients than control subjects. Urinary albumin excretion correlated positively with both mean blood pressure and left ventricular mass values in the absence of a relationship with circulating lipid and insulin levels. In contrast with microalbuminuria, sodium-hydrogen exchange covaried only with high-density lipoprotein cholesterol and insulin levels. Thus, microalbuminuria and an abnormal sodium-hydrogen exchange are unrelated phenomena in essential hypertensive patients. Microalbuminuria appears to be a hemodynamically driven biological variable, while an accelerated sodium-hydrogen exchange seems primarily conditioned by the metabolic abnormalities of hypertension, possibly in the context of an insulin-resistant syndrome.

Sodium-lithium countertransport has low affinity for sodium in hyperinsulinemic hypertensive subjects

We recently reported that incubation of red blood cells with insulin markedly decreases the affinity for external Na+ and increases the maximal transport rate (Vmax) of Na(+)-Li+ countertransport. The association of hypertension with insulin resistance and its compensatory hyperinsulinemia led us to investigate the relationship between insulin levels in vivo and the Na+ activation kinetics of this antiporter. We studied normotensive (n = 28) and hypertensive (n = 25) subjects after they had fasted overnight and determined their plasma glucose and insulin concentrations. Insulin levels were higher in the hypertensive subjects (11.7 +/- 1.5 microU/mL, mean +/- SEM) than in the normotensive subjects (8.2 +/- 1.2 microU/mL), but glucose levels were similar and within normal limits. Antiporter activity was measured as sodium-stimulated Li+ efflux by a new procedure that uses isosmotic conditions to raise external Na+ to 280 mmol/L. In normotensive subjects, Vmax was reached between 50 and 100 mmol/L Na+, whereas in most hypertensive subjects, Na+ concentrations higher than 150 mmol/L were needed. This different kinetic behavior was because the Na+ concentration for half-maximal activation (Km) was twofold higher in hypertensive subjects (58.9 +/- 5.3 mmol/L) than in normotensive subjects (29.8 +/- 2.6 mmol/L, P < .001). Hypertensive subjects with fasting insulin levels greater than 10 microU/mL (n = 12) had a higher Km for Na+ than subjects with insulin levels less than 10 microU/mL (n = 13) (73.4 +/- 8.7 versus 45.6 +/- 3.9 mmol/L, respectively, P < .01) and similar Vmax (0.57 +/- 0.05 versus 0.41 +/- 0.05 mmol.L-1.h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium countertransport and triglycerides in diabetic nephropathy

Elevated erythrocyte sodium-lithium countertransport (SLC) activity is an intermediate phenotype of essential hypertension among Caucasians, and is controversially associated with nephropathy in Type 1 (insulin-dependent) diabetes. Hypertriglyceridemia is a frequent concomitant of elevated SLC in the general population, and may be found in diabetic nephropathy. The present study was designed to investigate the influence of kidney disease, serum triglycerides and blood pressure on the interindividual variability of SLC in Type 1 diabetes. SLC and fasting major serum lipids were studied in 35 Type 1 diabetic patients with persistently elevated urinary albumin excretion and in a group of patients matched for age, sex and duration of diabetes, but with normoalbuminuria. SLC was elevated in patients with clinical nephropathy (N = 10; median: 420 mumol.1RBC-1.hr-1) and in patients with microalbuminuria (N = 25; median: 405 mumol.1RBC-1.hr-1) compared with normoalbuminuric patients (median: 296 mumol.1RBC-1.hr-1; P < 0.01 vs. both groups). Hypertriglyceridemia and hypercholesterolemia were found only among patients with macroalbuminuria. Analysis of covariance indicated that the association of elevated SLC with kidney disease (P < 0.006 in all models) was largely independent of serum triglycerides, but also of total cholesterol, insulin dose and measures of glycemic control. Only diastolic blood pressure was positively associated with SLC (P < 0.02) independently from nephropathy (P < 0.005) also after restricting analysis to the normoalbuminuric patients. Kidney disease and raised blood pressure remain major concomitants of elevated SLC in Type 1 diabetics.

Sodium-lithium countertransport activity in red blood cells of patients with IgA nephropathy

In this paper we report some results of our studies on patients with immunoglobulin (Ig)A nephropathy regarding (1) the familiar aggregation of erythrocyte sodium-lithium (Na,Li) countertransport; (2) the association of Na,Li countertransport with the presence of arterial hypertension and lipid abnormalities; (3) the correlation between Na,Li countertransport activity and renal functional reserve; and (4) the preliminary results of a longitudinal study. In 13 families of patients with IgA nephropathy, selected because both parents were available, we found a significant correlation between midparent and offspring Na,Li countertransport activity (Spearman's rank correlation = 0.65; P = 0.023), but no husband-wife relationship. In 49 patients, the activity of Na,Li countertransport was significantly higher in erythrocytes from 20 hypertensive patients than from either 29 normotensive patients or from 36 healthy age- and sex-matched normal subjects. Hyperlipidemic patients had an erythrocyte Na,Li countertransport activity significantly higher than normolipidemic patients and controls. In 17 patients a significant inverse correlation was found between the peak variation of creatinine clearance over baseline value after an oral protein load and the erythrocyte Na,Li countertransport activity (Spearman r = 0.54; P = 0.03). In a longitudinal study of 36 patients followed from 12 to 36 months, those showing a progression toward renal failure had an erythrocyte Na,Li countertransport activity higher than median value. The results of our studies show that in patients with IgA nephropathy a high erythrocyte Na,Li countertransport rate, genetically determined, is associated with the presence of arterial hypertension and lipid abnormalities, and perhaps with a less favorable disease outcome.

Membrane sodium-proton exchange and primary hypertension

Recent studies have revealed that an enhancement of sodium-proton exchange is a frequently observed ion transport abnormality in essential hypertension. An altered antiport activity not only is measurable in blood cells of hypertensive subjects ex vivo but also is detectable in skeletal muscle in vivo. Several lines of argument suggest that the altered antiport activity is not an epiphenomenon of hypertension: 1) the increased activity is found only in a subgroup of patients with high blood pressure, 2) it is not tightly correlated to the severity or duration of hypertension, and 3) high sodium-proton exchange activity persists over time and is not affected by antihypertensive treatment. Available evidence suggests that enhanced sodium-proton exchange is associated with or a cause for the structural alterations found in resistance vessels of hypertensive individuals (media hypertrophy) and left ventricular hypertrophy. This review summarizes some of the physiological properties and roles of the sodium-proton exchanger and discusses its kinetic properties in essential hypertension. Furthermore, the reasons for the enhanced antiport activity and its potential implications regarding the pathogenesis of hypertension are discussed.

Human lymphocyte sodium-hydrogen exchange. The influences of lipids, membrane fluidity, and insulin

The relation between serum lipids, membrane fluidity, insulin, and the activity of the sodium-hydrogen exchanger was investigated in human lymphocytes from 83 subjects. Subjects had a wide range of serum lipids and no concurrent disease. Lymphocyte membrane anisotropy (inversely related to membrane fluidity) was measured with a fluorescence polarization method. Sodium-hydrogen exchange maximal proton efflux rate, affinity for external sodium, and resting pH were determined with the intracellular pH-sensitive fluorochrome 2',5'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Sodium-hydrogen exchange maximal proton efflux rate was negatively correlated with the age of the subject (p = 0.03). Membrane anisotropy correlated with serum triglyceride (p = 0.04). Multiple regression analysis demonstrated that the maximal proton efflux rate in human lymphocytes was significantly related to age (p = 0.005), systolic blood pressure (p = 0.04), membrane anisotropy (p = 0.03), and serum cholesterol (p = 0.03). Incubation of lymphocytes with insulin failed to affect sodium-hydrogen exchange kinetics, intracellular buffering power, or resting intracellular pH. These results suggest that membrane-bound transport proteins may be influenced by serum lipids and the fluidity of the lipid membrane in which they are bound, but they are unlikely to be affected by insulin.

Relations of sodium-lithium countertransport kinetics to plasma and red cell membrane phospholipids in hyperlipidemia

As compared to 7 normolipidemic donors, the maximal velocity of sodium-lithium countertransport was accelerated by nearly 70% in 10 patients with elevated levels of triglyceride-rich lipoproteins and tended to be stimulated also in 5 patients with hypercholesterolemia. No significant differences were observed between normolipidemia and both hyperlipidemic groups for the apparent affinities of the transport system for intracellular sodium and extracellular lithium. Strong positive relations of the maximal activity of sodium-lithium countertransport to the percentages of red cell membrane phosphatidylcholine (r = 0.85, 2P < 0.001), the phosphatidylcholine/sphingomyelin (r = 0.82, 2P < 0.001) and the phosphatidylcholine/phosphatidylethanolamine ratio (r = 0.81, 2P < 0.001) were seen in all donors. A negative correlation was found to membrane sphingomyelin (r = -0.72, 2P < 0.001). Also plasma phosphatidylcholine and sphingomyelin exhibited positive and negative associations, respectively, to the maximal activity of sodium-lithium countertransport (r = 0.66, 2P < 0.01 and r = -0.78, 2P < 0.001). Among several plasma lipoprotein parameters investigated, total triglycerides or VLDL cholesterol levels showed independent relations to both the plasma and the membrane phosphatidylcholine/sphingomyelin ratio as well as to the maximal velocity of sodium-lithium countertransport. The results indicate that an increase in red cell membrane phosphatidylcholine and a concomitant fall in sphingomyelin are closely associated with the acceleration of sodium-lithium countertransport in hyperlipidemia.

Increased human erythrocyte sodium-lithium countertransport in hyperlipidaemic patients may indicate increased membrane lipid fluidity

Erythrocyte sodium-lithium countertransport (SLC) activity, membrane fluidity, plasma triglyceride and cholesterol were measured in hyperlipidaemic patients and normal subjects. Fluidity was assessed by the fluorescence anisotropy (inversely related to fluidity) of the probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1,4-trimethylammonium-3,5-hexatriene (TMA-DPH). In a second group of patients the maximum velocity (Vmax) and external sodium affinity constant (km) of SLC was also measured. In the first group of patients, SLC activity was increased compared with the controls (0.279 +/- 0.019 vs. 0.213 +/- 0.013, P = 0.006) as was membrane fluidity in the deep hydrophobic regions (DPH anisotropy 0.211 +/- 0.0007 vs. 0.215 +/- 0.0011, P = 0.007). There was a strong correlation between SLC and DPH anisotropy (Rs = -0.72, P = < 0.001) which was due to the correlation between Vmax and DPH anisotropy (Rs = -0.90, P = < 0.001). Increases in Vmax of SLC in hyperlipidaemic patients may be due to differences in lipid organisation in the deep hydrophobic regions of the membrane which may affect the turnover rate of the transporter.

Erythrocyte sodium-lithium countertransport activity and total body insulin-mediated glucose disposal in normoalbuminuric normotensive type 1 (insulin-dependent) diabetic patients

Insulin resistance in Type 1 (insulin-dependent) diabetes mellitus may be associated with raised erythrocyte sodium-lithium countertransport activity in patients with hypertension, or nephropathy, or both. However, in these circumstances it is difficult to separate the impact of hypertension, hyperlipidaemia and nephropathy on erythrocyte sodium-lithium countertransport from that of insulin resistance. We have therefore examined the relationship between insulin-mediated glucose disposal and erythrocyte sodium-lithium countertransport in 41 normotensive (mean blood pressure 120/74 mmHg), normoalbuminuric (mean albumin excretion 6.2 micrograms/min), normolipidaemic (mean serum cholesterol 4.3 mmol/l and mean serum triglycerides 1.0 mmol/l) Type 1 diabetic patients. Erythrocyte sodium-lithium countertransport was on average 0.31 mmol Li.h-1.l erythrocytes-1 (range 0.07-0.69). Nine patients had values above 0.40 mmol Li.h-1.l erythrocytes-1 (0.51 +/- 0.10 mmol Li.h-1.l erythrocytes-1). The patients with high erythrocyte sodium-lithium countertransport were matched for age, sex, BMI, HbA1 and duration of diabetes, with nine patients with normal erythrocyte sodium-lithium countertransport. Insulin-mediated glucose disposal was evaluated during the last hour of a euglycaemic clamp (insulin 0.015 U.kg-1.h-1; blood glucose clamped at 7.0 mmol/l). The free insulin levels were comparable between the patients with high and normal erythrocyte sodium-lithium countertransport (37.2 +/- 14.7 mU/l and 34.7 +/- 17.2 mU/l respectively). Insulin-mediated glucose disposal was on average 3.1 +/- 1.5 (range 0.8-6.8) mg.kg-1.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lipids affect maximum velocity not sodium affinity of human sodium-lithium countertransport: distinction from essential hypertension

Inheritance is a major determinant of increased sodium-lithium countertransport (SLC) activity in hypertension. However, hyperlipidaemia can also cause increased SLC activity in some individuals and it is difficult to distinguish this effect from the effect of hypertension. Erythrocyte SLC activity and its kinetic determinants sodium affinity (km) and maximum velocity (Vmax) were measured in 25 hyperlipidaemic patients and 15 normal controls (NC). Increased SLC activity (0.31 +/- SEM 0.03 mmol Li/(h x 1 cells) vs. NC 0.20 +/- 0.01, P < 0.01) in the hyperlipidaemic patients was associated with increased Vmax (0.59 +/- 0.07 vs. NC 0.41 +/- 0.03, P < 0.01) but normal km (median 120 range [40-324] mmol l-1 vs. 140 [108-260]. Lipid-lowering therapy resulted in decreased SLC activity secondary to a fall in Vmax. Km remained constant despite the changes in lipids and Vmax. The mechanism of increased SLC activity in hyperlipidaemia is different from that in essential hypertension where increased sodium affinity is found. Measurement of the kinetic characteristics of SLC may discriminate between the independent influences of hypertension and hyperlipidaemia on the sodium-lithium countertransporter.

Serum triglyceride and insulin levels are associated with erythrocyte sodium-lithium counter-transport activity in normoglycaemic individuals

The relationship between erythrocyte sodium-lithium counter-transport activity, serum insulin, lipids and demographic factors was examined in 93 normoglycaemic predominantly normotensive individuals with mild fasting hypercholesterolaemia (greater than 5.2 mmol/l). The major significant univariate correlates of sodium-lithium counter-transport activity were fasting serum triglycerides, HDL cholesterol, the ratio of fasting glucose: insulin, apo A1, alcohol consumption and apo B. Stepwise multiple regression analysis revealed 24% of the variability in sodium-lithium counter-transport activity could be accounted for by independent contributions of fasting serum triglycerides, alcohol consumption, the fasting glucose/insulin ratio and apo A1 and ANOVA confirmed a significant relationship with fasting insulin measures that was independent of serum triglycerides (P less than 0.05). The relationship between erythrocyte sodium-lithium counter-transport activity and concentrations of serum triglycerides, HDL components, insulin and additionally alcohol consumption, could reflect the influence of those variables on erythrocyte structure and function.

Effects induced by olive oil-rich diet on erythrocytes membrane lipids and sodium-potassium transports in postmenopausal hypertensive women

Since we have observed that monounsaturated fatty acids (MUFA) enriched diet modifies red cell membrane lipids and cation transport systems in normotensive subjects, we similarly evaluated a group of hypertensive patients undergoing an analogous dietary modification. In a group of 18 moderately hypertensive women, the diet was supplemented for two months with olive oil (about 45 g/day), which replaced an equal amount of seasoning fats. Before and after this period, red cell fatty acid composition was evaluated by gas-chromatography in order to verify diet compliance: a significant increase in oleic acid was observed, while the content of saturated and polyunsaturated fatty acids remained unchanged. After olive oil, maximal rates of Na-K pump (5580 +/- 329 vs 6995 +/- 390, p less than 0.001) and Na-K cotransport (Na-COT 544 +/- 52 vs 877 +/- 46, p less than 0.001: K-COT 790 +/- 76 vs 1176 +/- 66, p less than 0.001), cell Na content (9.58 +/- 0.4 vs 10.61 +/- 0.6, p less than 0.03) and passive permeability for Na (936 +/- 74 vs 1836 +/- 102, p less than 0.001) rose significantly. Although the reduction in maximal rate of the Li-Na CT after olive oil was not significant, it was the only cation transport parameter being correlated with the variations of membrane lipids, namely negatively with UFA (r = -0.528, p less than 0.05) and positively with SFA (r = 0.482, p less than 0.005). The change in maximal rate of Li-Na CT was also correlated with the variation of systolic and diastolic BP (r = 0.50, p less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Is increased erythrocyte sodium-lithium countertransport a useful marker for diabetic nephropathy?

Genetic predisposition to essential hypertension has been proposed as a risk factor for the development of diabetic nephropathy in type 1 (insulin-dependent) diabetes mellitus. An increased sodium-lithium countertransport activity (NaLiCT) has been suggested as a genetic marker for essential hypertension. We therefore evaluated NaLiCT in diabetic patients with (N = 39) or without (N = 23) diabetic nephropathy (DNP), patients with non-diabetic renal diseases (N = 42) and in healthy controls (N = 24). The NaLiCT was elevated in both diabetic patient groups compared to healthy controls (median 244; range 134 to 390 mumol.liter cells-1.hr-1), but was not different in patients with DNP (median 314; range 162 to 676), without DNP (median 325; range 189 to 627) and patients with non-diabetic renal disease (median 300; range 142 to 655). The genetic predisposition to DNP is illustrated by the fact that diabetic sibs of probands with DNP showed a higher occurrence of DNP than diabetic sibs of patients without DNP. We analyzed whether familial DNP clustered with an increased NaLiCT. The NaLiCT in sibs concordant for the presence of DNP (N = 10; median 307; range 217 to 428 mumol.liter cells-1.hr-1) was not significantly different from that in sibs concordant for absence of DNP (N = 15; median 279; range 189 to 442). We conclude that erythrocyte sodium-lithium countertransport activity cannot be used as a marker to identify patients at risk for the development of diabetic nephropathy.

Clustering of risk factors in hypertensive insulin-dependent diabetics with high sodium-lithium countertransport

Diabetic nephropathy is more common in patients with a positive family history of hypertension and with elevated red blood cell sodium-lithium countertransport, a marker of risk for essential hypertension. To evaluate whether there is a relationship between this cation transport system and indicators of risk of renal and cardiovascular complications in diabetic patients before the development of clinical proteinuria, we studied 31 type 1 (insulin-dependent) diabetic patients with arterial hypertension, without clinical proteinuria and 12 normotensive normoalbuminuric diabetic patients. Sodium-lithium countertransport activity was significantly higher in hypertensive patients (0.43 +/- 0.03 mmol/l RBC x hr) than in normotensive patients (0.23 +/- 0.03; P less than 0.001). To better explore the nature of the association between this transport system and arterial hypertension, hypertensive patients were divided in two groups, with high (greater than 0.41 mmol/l RBC x hr) or normal (less than 0.41) sodium-lithium countertransport activity. The two groups of hypertensive diabetics were similar in age, sex, body mass index and blood pressure levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium countertransport and body fat distribution

The relationship between erythrocyte sodium-lithium countertransport (Na-Li CT) and body fat distribution is analyzed in a sample (n = 101) of normotensive and untreated hypertensive men participating in an epidemiological study of coronary heart disease risk factors. Na-Li CT is significantly and positively associated with both subscapular skinfold and waist to hip ratio, but not with triceps skinfold. The univariate correlation between Na-Li CT and blood pressure is diminished when adjusted for body mass index and waist to hip ratio. These findings support the existence of an association between Na-Li CT and central body fat distribution and suggest that the metabolic abnormalities associated with centrally distributed body fat could explain, at least in part, the association between Na-Li CT and blood pressure. The maximal velocity of the sodium-lithium countertransport (Na-Li CT) in erythrocytes has been reported to be directly associated with blood pressure and hypertension in numerous reports from both clinical and epidemiological studies. In most of these studies, indices of weight and/or adiposity (body mass index, in particular) have been shown to be among the most important correlates of Na-Li CT. Adiposity is an important determinant of blood pressure, and there is evidence suggesting that the patterning of the fat cells in the body is linked to a number of metabolic disturbances that could lead to hypertension and an increase in other CHD risk factors. The present report analyses the relationship between Na-Li CT and body fat distribution in a sample of normotensive and untreated hypertensive men participating in an epidemiological study.

Sodium-lithium countertransport kinetics in normal and hypertensive human pregnancy

Erythrocyte sodium-lithium countertransport activity is increased in a subgroup of patients with essential hypertension but activity also rises temporarily during normal pregnancy. It is not known if the mechanism of raised activity is the same in both of these situations. Standard sodium-lithium countertransport activity and its kinetic characteristics (sodium affinity and maximum velocity) were measured in 15 women with a normal pregnancy. The mechanism of raised sodium-lithium countertransport activity was an increase in maximum velocity. There was no change in sodium affinity. This contrasts with essential hypertension where the mechanism is increased sodium affinity. Sodium-lithium countertransport activity was also measured in 14 primigravidae whose pregnancies were complicated by hypertension, and mean activity was not significantly higher than in normal pregnancy. However, six women had increased sodium affinity suggestive of essential hypertension and a different underlying mechanism of hypertension to those with normal sodium affinity. Prospective measurement of sodium-lithium countertransport kinetics may lead to a better understanding of the pathophysiology of hypertension in pregnancy.

Increased sodium-lithium countertransport activity in red cells of IgA nephropathy patients

The aim of this work was to analyze Na,Li countertransport activity in the erythrocytes from patients with IgA nephropathy, in relationship with their blood pressure status and lipid profile. Forty-nine patients (32 males, 17 females) with biopsy-proven IgA nephropathy and without significant impairment of renal function (serum creatinine less than or equal to 1.4 mg/dl) and 36 normal subjects (21 males, 15 females) were evaluated. Twenty-nine patients with IgA nephropathy were normotensive and 20 hypertensive (diastolic pressure greater than or equal to 95 mm Hg or treated by antihypertensive drugs). Na,Li countertransport was significantly higher in red cells from hypertensive than from normotensive patients (P = 0.002) and normal subjects (P = 0.0001), (values respectively 309 +/- 17; 241 +/- 12 and 211 +/- 11 mumol/liter RBC/hr); normotensive patients with IgA nephropathy did not differ from controls regarding the Na,Li countertransport rate. A multiple stepwise logistic regression analysis with blood pressure status as the dependent variable and Na,Li countertransport activity, age, serum creatinine, proteinuria, cholesterol, triglycerides, plasma potassium and time from onset as independent variables, indicated an independent significant association for Na,Li countertransport (P = 0.002) proteinuria (P = 0.006), plasma potassium (P = 0.006) and age (P = 0.029). Other tested variables were not independently related to blood pressure status. Hyperlipidemic patients (plasma total cholesterol concentration greater than 200 mg/dl and/or plasma triglycerides greater than 172 mg/dl) had an erythrocyte Na,Li countertransport activity significantly higher than normolipidemic (P = 0.005) and controls (P = 0.001) (values respectively 295 +/- 14; 226 +/- 12 and 211 +/- 11 mumol/liter RBC/hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlates of sodium-lithium countertransport. Findings from the Gubbio Epidemiological Study. The Gubbio Collaborative Study Group

BACKGROUND

Numerous reports have presented evidence for a positive association between the maximal velocity of the sodium-lithium countertransport (Na-Li CT) in erythrocytes and hypertension. The nature of this association remains to be clarified.

METHODS AND RESULTS

This report presents correlates of Na-Li CT in a population sample of 3,591 people aged 5-74 years. Males had higher mean age-specific levels of Na-Li CT than females except for the 5-14-year age stratum. In adults aged 25-74, for both men (n = 1,044) and women (n = 1,192), body mass index, plasma uric acid and glucose, alcohol consumption, and red blood cell mean corpuscular volume were positively related to countertransport in multivariate analyses; plasma high-density lipoprotein (HDL) cholesterol and plasma potassium were inversely related. Plasma non-HDL cholesterol was independently and directly related to Na-Li CT in women, and plasma sodium was inversely associated with Na-Li CT in men. These relations prevailed for men when persons with hypertension were excluded from the analyses and prevailed in part for women. When stepwise regression analyses were done for all men and women combined (n = 2,236), sex ceased to be significantly related to countertransport with plasma uric acid and alcohol intake in the model. In adults of either sex, no independent association was detected between Na-Li CT and age, heart rate, or the ratios of sodium to potassium or of sodium to creatinine in overnight untimed urine.

CONCLUSIONS

In both sexes, Na-Li CT is significantly and independently associated with a number of metabolic variables (plasma uric acid, plasma glucose, body mass index, plasma potassium, and life-style habits [e.g., alcohol intake]). Further research is needed to elucidate the meaning of the significant associations between Na-Li CT and the foregoing variables (all of them also related to blood pressure).

Lipid lowering therapy leads to a reduction in sodium-lithium countertransport activity

Erythrocyte sodium-lithium countertransport (SLC) was measured in 17 patients with either combined hyperlipidaemia or hypercholesterolaemia before and after lipid lowering therapy. Before treatment SLC related to the serum triglyceride level and was increased in combined hyperlipidaemia. After treatment the SLC had returned to normal and the change in SLC was related to the change in serum triglyceride levels. Raised SLC is associated with essential hypertension but is not related to blood pressure. Therefore, the association of raised SLC with hyperlipidaemia and essential hypertension appears to have different underlying mechanisms.

Sodium lithium countertransport is acutely influenced by heparin-induced extracorporal LDL precipitation

Sodium lithium countertransport may be a genetic marker for arterial hypertension and for the risk of diabetic nephropathy in type 1 diabetic patients. Since various factors seem to influence the transport velocity including serum lipid alterations, erythrocytes of seven patients with severe hyperlipoproteinaemia who were chronically and intermittently treated with LDL apheresis were examined before and immediately after therapy. The LDL apheresis reduced sodium lithium countertransport significantly (0.383 vs 0.269, P less than 0.02). Therefore, we conclude that serum lipid composition must be considered when interpreting sodium lithium countertransport velocity.

Kinetic abnormalities of the red blood cell sodium-proton exchange in hypertensive patients

The present study was designed to examine the kinetics of Na(+)-H+ exchange in red blood cells of normotensive and hypertensive subjects and its relation to the previously reported abnormalities in Na(+)-Li+ exchange. The Na(+)-H+ antiporter activation kinetics were studied by varying cell pH and measuring net Na+ influx (mmol/l cell x hr = units) driven by an outward H+ gradient. The Na(+)-Li+ exchange was determined at pH 7.4 as sodium-stimulated Li+ efflux. Untreated hypertensive patients (n = 30) had a higher maximal rate of Na(+)-Li+ exchange (0.43 +/- 0.05 versus 0.26 +/- 0.02 units, p less than 0.0003), a higher maximal rate of Na(+)-H+ exchange (62.3 +/- 6.2 versus 47 +/- 4 units; p less than 0.02), but a similar affinity for cell pH compared with normotensive subjects (n = 46). The cell pH activation of the Na(+)-H+ antiporter exhibited a lower Hill coefficient than that of normotensive subjects (1.61 +/- 0.12 versus 2.56 +/- 0.14; p less than 0.0001). This index of occupancy of internal H+ regulatory sites was found reduced in most of the hypertensive patients (73%) whether their hypertension was untreated or treated. Hypertensive patients with Na(+)-Li+ exchange above 0.35 units (0.68 +/- 0.057 units, n = 16) did not exhibit elevated maximal rates of Na(+)-H+ exchange (57.3 +/- 10 units, NS) in comparison with those with Na(+)-Li+ exchange below 0.35 units (66.4 +/- 7.6 units, n = 26), but both groups exhibited reduced Hill coefficients. Hypertensive patients with enhanced Na(+)-H+ exchange activity (more than 90 units) had normal maximal rates of Na(+)-Li+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lovastatin treatment on red blood cell and platelet cation transport

Hypercholesterolemia frequently accompanies hypertension, and it has been suggested that by affecting membrane lipid composition, hypercholesterolemia may cause or accentuate abnormalities in several red blood cell transports associated with hypertension. Such an effect might obfuscate the relation of membrane markers to hypertension and decrease their usefulness in genetic studies of the heritable basis of hypertension. To determine if changing plasma lipids affects membrane transport, we studied the effects of the cholesterol-lowering agent lovastatin on red blood cell lithium-sodium countertransport and sodium-potassium-chloride cotransport, red blood cell sodium and water content, and platelet amiloride-sensitive volume responsiveness to cytoplasmic acidification, an indirect measure of sodium-proton exchange that has been proposed as a new membrane marker for hypertension. In a 24-week, placebo-controlled, double-blinded, randomized trial, lovastatin significantly lowered total and low density lipoprotein cholesterol and raised high density lipoprotein cholesterol. Red blood cell lithium-sodium countertransport and sodium-potassium-chloride cotransport were not significantly altered. Red blood cell sodium content decreased significantly in the lovastatin-treated group, probably as a result of an increase in red blood cell sodium-potassium pump activity. Platelet amiloride-sensitive responses to cytoplasmic acidification were significantly depressed by lovastatin treatment, suggesting that lowering plasma cholesterol may suppress platelet sodium-proton exchange. It has been hypothesized that the hyperlipidemias frequently observed in essential hypertensive patients may alter membrane lipid composition and affect membrane cation transport activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Red cell Na+/Li+ countertransport in non-insulin-dependent diabetics with diabetic nephropathy

Genetic predisposition to essential hypertension, as indicated by increased maximal velocity of Na+/Li+ countertransport in red cells, has been suggested as a marker for the risk of developing diabetic nephropathy. To evaluate the validity of this concept in non-insulin-dependent diabetics, we measured the maximal velocity of Na+/Li+ countertransport in red cells in 18 male diabetics suffering from proteinuria due to biopsy proven diabetic glomerulosclerosis (GFR: 51 [range 27 to 146] ml/min/1.73 m2), 17 male diabetics with normoalbuminuria, and in 18 sex-, age-, and body mass index-matched healthy control subjects. Na+/Li+ countertransport was identical in patients with and without diabetic nephropathy, 0.43 (0.24 to 0.92) versus 0.44 (0.20 to 0.83) mmol/(liter cells x hr), but was elevated compared to control subjects, 0.32 (0.09 to 0.73; P less than 0.05). Arterial blood pressure was elevated in patients with nephropathy (162/92 +/- 21/9 mm Hg) compared to normoalbuminuric patients (132/82 +/- 15/7) and control subjects (133/83 +/- 14/7 mm Hg; P less than 0.001). Our study does not support the hypothesis that the risk of diabetic nephropathy in non-insulin-dependent diabetes is associated with a genetic predisposition to hypertension. Diabetes per se seems to enhance Na+/Li+ countertransport activity.

Sodium-lithium countertransport activity in red cells of patients with insulin dependent diabetes and nephropathy and their parents

OBJECTIVE

To determine whether there are familial and genetic aspects of sodium-lithium countertransport activity in red cells in diabetic nephropathy.

DESIGN

Case-control study.

SETTING

Teaching hospital diabetic clinic.

SUBJECTS

40 Patients with insulin dependent diabetes, both of whose parents were alive: 20 with persistent proteinuria and 20 with normal albumin excretion matched for age, duration of diabetes, and body mass index. All 80 parents.

MAIN OUTCOME MEASURES

Sodium-lithium countertransport activity in red cells and arterial blood pressure.

RESULTS

Sodium-lithium countertransport activity in red cells was higher in the patients with proteinuria than in the patients with normoalbuminuria (mean (95% confidence interval) 0.47 (0.39 to 0.54) v 0.33 (0.28 to 0.38) mmol/l red cells/h respectively, p = 0.0036; mean difference 0.14 (0.04 to 0.22)). The mean countertransport activity for the two parents of each patient was calculated, and from this the mean value for each group of parents was calculated; the value was higher in the parents of the patients with proteinuria than in the parents of the patients with normoalbuminuria (0.40 (0.32 to 0.48) v 0.30 (0.26 to 0.33) mmol/l red cells/h respectively, p = 0.016; 0.10 (0.02 to 0.19)). Twenty-eight of the parents of the patients with proteinuria compared with 12 of the parents of the patients with normoalbuminuria had a countertransport activity that was above the median value in all 80 parents (p less than 0.001). Mean arterial blood pressure in the parents of the patients with proteinuria was related to that of their offspring (r = 0.46; p less than 0.01). There was a positive correlation between the sodium-lithium countertransport activity in red cells in the parents and their offspring when all parents and patients were considered (r = 0.37; p less than 0.001).

CONCLUSIONS

Increased sodium-lithium countertransport activity in red cells in the parents of diabetic patients with nephropathy provides further evidence that familial, and possibly genetic, factors related to a predisposition to arterial hypertension have a role in the susceptibility of diabetic renal disease.

Sodium-lithium countertransport in microalbuminuric insulin-dependent diabetic patients

A familial predisposition to arterial hypertension has recently been suggested as one important component of the susceptibility to diabetic kidney disease. Sodium-lithium countertransport activity, a marker of risk for essential hypertension, has been found to be increased in diabetic patients with overt nephropathy. We have measured red blood cell sodium-lithium counter-transport activity in 36 microalbuminuric insulin-dependent diabetic patients, a group at high risk of progression to clinical nephropathy and cardiovascular disease, and compared it with that of a matched group of 36 normoalbuminuric diabetic patients. Sodium-lithium countertransport was higher in the microalbuminuric (0.43 [95% confidence interval (CI) 0.38-0.47] mmol/l red blood cells [RBC]/hr) than in the normoalbuminuric diabetic patients (0.29 [0.25-0.33] mmol/l RBC/hr, mean difference 0.14 [0.08-0.20]; p less than 0.0001). Microalbuminuric patients had a higher frequency of parental hypertension than normoalbuminuric diabetic patients (56% vs. 28%, p less than 0.05). Sodium-lithium countertransport was related to mean arterial pressure in the microalbuminuric patients (r = 0.54, p less than 0.001) and to daily insulin requirements in both groups (microalbuminuric patients r = 0.39, p less than 0.05; normoalbuminuric patients r = 0.42, p less than 0.01). In a subset of patients in whom lipoproteins were measured, sodium-lithium countertransport activity was related to total and very low density lipoprotein triglycerides (r = 0.41, p less than 0.05 and r = 0.48, p less than 0.05) and to apolipoprotein B (r = 0.56, p less than 0.05), independently of body mass index, albumin excretion rate, glycemic control, and insulin dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Transmembrane cation fluxes and fatty acid composition of erythrocytes in psoriatic patients

Cation transport systems and lipid composition of erythrocyte membrane were studied in 27 psoriatic patients and in 34 healthy individuals. Whereas intracellular Na and K content, Na- and K-passive permeability and Li-Na countertransport of psoriatics did not show any statistical difference from normals, the Na/K ATPase pump activity was significantly higher and Na-K cotransport was significantly lower. Membrane lipid composition of psoriatics was different from normals: an increase in arachidonic acid and in unsaturated (poly- and total unsaturated) fatty acid content was found. A positive correlation was demonstrated between unsaturated/saturated fatty acid ratio and Na/K ATPase pump activity. These results demonstrate an alteration of erythrocyte Na/K ATPase pump and Na-K cotransport in psoriasis. These alterations of cation transport are associated with a perturbation of membrane fatty acid composition which appears a widespread phenomenon in cells of psoriatic patients.

Red blood cell lithium-sodium countertransport in non-modulating essential hypertension

Abnormalities in erythrocyte Li-Na countertransport have been reported in hypertensive subjects, and the available evidence favors familial aggregation and striking heritability of this marker. It is uncertain, however, whether the abnormalities are associated with hypertension per se or whether they may be concentrated in a particular subset of hypertensive subjects. In the present study, maximal rates of Li-Na countertransport were measured in red blood cells of 82 white subjects, including 37 normotensive subjects and 45 normal- or high-renin hypertensive subjects previously classified as non-modulators (n = 21) or modulators (n = 24). Mean countertransport activity was significantly higher in non-modulators compared with normally modulating hypertensive or normotensive subjects (0.475 +/- 0.044 vs. 0.309 +/- 0.028 or 0.249 +/- 0.012 mmol/l cell x hr, respectively, p less than 0.001). Modulators did not differ significantly from normotensive subjects with regard to mean countertransport activity. Red blood cell sodium pump and Na-K-Cl cotransport were not significantly different in modulating and non-modulating hypertensive subjects. These relations remained unchanged after adjusting for age, body weight, and plasma cholesterol levels by analysis of covariance. A countertransport value exceeding 0.50 mmol/l cell x hr occurred in 40% of the non-modulators but in only one of the other subjects. In contrast , while one half of the modulators and normotensive subjects had a countertransport value less than 0.235 mmol/l cell x hr, none of the non-modulators did. Thus, elevated countertransport appears to aggregate in the non-modulating subset of essential hypertensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane fatty acids and erythrocyte Li-Na countertransport in nephrotic syndrome and their relationship

Cholesterol/phospholipids molar ratio and fatty acid composition have been estimated in erythrocyte membrane of 12 patients suffering from nephrotic syndrome and compared to values obtained in 23 normal subjects matched for sex and age. The membrane lipid composition has been correlated with the activity of erythrocyte Li-Na countertransport of the same subjects. The results show a significant increase in cholesterol/phospholipids ratio and total saturated fatty acids when erythrocytes of nephrotic patients are compared to normal erythrocytes, whereas total unsaturated fatty acids were lower in nephrotics (p less than 0.002). Li-Na countertransport was higher in nephrotics (p less than 0.001) and it was positively correlated with the total amount of saturated fatty acids of the erythrocyte membrane (r = +0.451; p less than 0.01). On the contrary, Li-Na countertransport was negatively correlated with the total amount of unsaturated fatty acids (r = -0.468; p less than 0.01).

Red-cell sodium-lithium countertransport and fractional excretion of lithium in normal and hypertensive humans

To examine the relations between erythrocyte sodium-lithium countertransport and renal proximal tubular sodium handling, we measured countertransport, and then subjected 30 normal and 32 hypertensive subjects, both white and black, to provocative maneuvers of volume expansion and contraction. The fractional excretions of sodium and lithium were measured simultaneously. In agreement with previous studies, we found that countertransport in erythrocytes was elevated in hypertensive patients compared with normal subjects. We also observed that whites have a higher level of countertransport than blacks. In the basal state, we found that fractional sodium excretion of hypertensive patients was no different than in normal subjects, whereas the fractional lithium excretion of hypertensive persons was increased compared with normotensive values. Volume expansion with 2 1 0.9% saline administered intravenously during a 4-hour period provoked an exaggerated natriuresis and a greater increase in fractional lithium clearance in hypertensive patients compared with the control group. With volume expansion and contraction, fractional lithium clearance and countertransport were directly correlated. Our data suggest that hypertensive persons do not have increased proximal tubular sodium reabsorption compared with normal subjects. Further, the exaggerated natriuresis of hypertension is, in part, the result of increased distal solute delivery. The fact that our hypertensive patients were older may partially explain the discrepancies between this report and previous observations.

Erythrocyte sodium-lithium countertransport in primary and renal hypertension: relation to family history

Sodium-lithium countertransport (Na-Li CT) has been reported to be increased in essential hypertension (EHT) but the nature and degree of distinction from normal controls in unclear. Of 44 unselected patients with EHT in the hospital hypertension clinic 36% had Na-Li CT greater than the normal control range and 70% of these had a family history of hypertension. Almost all the patients with normal Na-Li CT had no family history of hypertension. Analysis of variance showed that raised Na-Li CT was related to both a family history of hypertension and a family history of a cardiovascular event. Of 23 patients with hypertension secondary to renal disease, 43% had Na-Li CT greater than the normal control range and raised Na-Li CT was related to both a family history of hypertension and a family history of cardiovascular event in the same way as EHT. Raised Na-Li CT was not characteristic of EHT but identified a subgroup of patients with EHT and a family history of hypertension, some of whom also had renal disease.