Effect of exercise on cation transport in human red cells

Walking for hypertension

BACKGROUND

Increased physical activity has been recommended as an important lifestyle modification for the prevention and control of hypertension. Walking is a low-cost form of physical activity and one which most people can do. Studies testing the effect of walking on blood pressure have revealed inconsistent findings.

OBJECTIVES

To determine the effect of walking as a physical activity intervention on blood pressure and heart rate.

SEARCH METHODS

We searched the following databases up to March 2020: the Cochrane Hypertension Specialised Register, CENTRAL (2020, Issue 2), Ovid MEDLINE, Ovid Embase, CINAHL, PsycINFO, SPORTDiscus, PEDro, the WHO International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also searched the following Chinese databases up to May 2020: Index to Taiwan Periodical Literature System; National Digital Library of Theses and Dissertation in Taiwan; China National Knowledge Infrastructure (CNKI) Journals, Theses & Dissertations; and Wanfang Medical Online. We contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions.

SELECTION CRITERIA

Randomised controlled trials of participants, aged 16 years and over, which evaluated the effects of a walking intervention compared to non-intervention control on blood pressure and heart rate were included.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Where data were not available in the published reports, we contacted authors. Pooled results for blood pressure and heart rate were presented as mean differences (MDs) between groups with 95% confidence intervals (CIs). We undertook subgroup analyses for age and sex. We undertook sensitivity analyses to assess the effect of sample size on our findings.

MAIN RESULTS

A total of 73 trials met our inclusion criteria. These 73 trials included 5763 participants and were undertaken in 22 countries. Participants were aged from 16 to 84 years and there were approximately 1.5 times as many females as males. The characteristics of walking interventions in the included studies were as follows: the majority of walking interventions was at home/community (n = 50) but supervised (n = 36 out of 47 reported the information of supervision); the average intervention length was 15 weeks, average walking time per week was 153 minutes and the majority of walking intensity was moderate. Many studies were at risk of selection bias and performance bias. Primary outcome We found moderate-certainty evidence suggesting that walking reduces systolic blood pressure (SBP) (MD -4.11 mmHg, 95% CI -5.22 to -3.01; 73 studies, n = 5060). We found moderate-certainty evidence suggesting that walking reduces SBP in participants aged 40 years and under (MD -4.41 mmHg, 95% CI -6.17 to -2.65; 14 studies, n = 491), and low-certainty evidence that walking reduces SBP in participants aged 41 to 60 years (MD -3.79 mmHg, 95% CI -5.64 to -1.94, P < 0.001; 35 studies, n = 1959), and those aged 60 years of over (MD -4.30 mmHg, 95% CI -6.17 to -2.44, 24 studies, n = 2610). We also found low certainty-evidence suggesting that walking reduces SBP in both females (MD -5.65 mmHg, 95% CI -7.89 to -3.41; 22 studies, n = 1149) and males (MD -4.64 mmHg, 95% CI -8.69 to -0.59; 6 studies, n = 203). Secondary outcomes We found low-certainty evidence suggesting that walking reduces diastolic blood pressure (DBP) (MD -1.79 mmHg, 95% CI -2.51 to -1.07; 69 studies, n = 4711) and heart rate (MD -2.76 beats per minute (bpm), 95% CI -4.57 to -0.95; 26 studies, n = 1747). We found moderate-certainty evidence suggesting that walking reduces DBP for participants aged 40 years and under (MD -3.01 mmHg, 95% CI -4.44 to -1.58; 14 studies, n = 491) and low-certainty evidence suggesting that walking reduces DBP for participants aged 41 to 60 years (MD -1.74 mmHg, 95% CI -2.95 to -0.52; 32 studies, n = 1730) and those aged 60 years and over (MD -1.33 mmHg, 95% CI -2.40 to -0.26; 23 studies, n = 2490). We found moderate-certainty evidence that suggests walking reduces DBP for males (MD -2.54 mmHg, 95% CI -4.84 to -0.24; 6 studies, n = 203) and low-certainty evidence that walking reduces DBP for females (MD -2.69 mmHg, 95% CI -4.16 to -1.23; 20 studies, n = 1000). Only 21 included studies reported adverse events. Of these 21 studies, 16 reported no adverse events, the remaining five studies reported eight adverse events, with knee injury being reported five times.

AUTHORS' CONCLUSIONS

Moderate-certainty evidence suggests that walking probably reduces SBP. Moderate- or low-certainty evidence suggests that walking may reduce SBP for all ages and both sexes. Low-certainty evidence suggests that walking may reduce DBP and heart rate. Moderate- and low-certainty evidence suggests walking may reduce DBP and heart rate for all ages and both sexes.

Erythrocyte sodium-lithium countertransport activity is inversely correlated to adiponectin, retinol binding protein 4 and body height

BACKGROUND

We have previously described that the sodium/lithium countertransport (SLC) in the erythrocyte cell membrane is closely linked to obesity and insulin resistance. Adiponectin and retinol-binding protein 4 (RBP-4) are believed to affect obesity and insulin resistance. In the present study, we aimed to further characterize the relationship between SLC, inflammatory markers, adiponectin and RBP-4.

METHODS

We included 93 clinically healthy 58-year-old men selected to display variations in insulin sensitivity. High sensitivity C-reactive protein (hs-CRP), TNF-alpha, soluble TNF-alpha-receptors (sTNFR) 1 and 2, IL-6 and RBP-4 were measured using antibody-based techniques. Adiponectin was determined by a radioimmunoassay kit. The lithium concentration in the special flux medium was measured by atomic absorption spectrophotometry.

RESULTS

In univariate analyses, SLC correlated negatively with RBP-4 (r(s) = -0.256, p = -0.017) and to adiponectin (r(s) = -0.316, p = 0.003) and positively with TNF-alpha (r(s) = 0.346, p = 0.001) and hs-CRP (r(s) = 0.288, p = 0.005). There were no statistically significant correlations with sTNFR 1 or 2 or IL-6. SLC was negatively associated to body height (r(s) = -0.256, p = 0.013).

CONCLUSIONS

We are the first to report that SLC correlates negatively with adiponectin and RBP-4. This finding is intriguing, as adiponectin is anti-inflammatory and anti-diabetic whereas RBP-4 supposedly decreases insulin sensitivity. We also observed a negative association between SLC activity and body height indicating that SLC activity is not primarily influenced by fat mass. The positive association of SLC with markers of inflammatory activity such as TNF-alpha and hs-CRP is in line with the proposed link between inflammation and insulin resistance.

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.

Physiology and pathophysiology of Na+/H+ exchange and Na+ -K+ -2Cl- cotransport in the heart, brain, and blood

Maintenance of a stable cell volume and intracellular pH is critical for normal cell function. Arguably, two of the most important ion transporters involved in these processes are the Na+/H+ exchanger isoform 1 (NHE1) and Na+ -K+ -2Cl- cotransporter isoform 1 (NKCC1). Both NHE1 and NKCC1 are stimulated by cell shrinkage and by numerous other stimuli, including a wide range of hormones and growth factors, and for NHE1, intracellular acidification. Both transporters can be important regulators of cell volume, yet their activity also, directly or indirectly, affects the intracellular concentrations of Na+, Ca2+, Cl-, K+, and H+. Conversely, when either transporter responds to a stimulus other than cell shrinkage and when the driving force is directed to promote Na+ entry, one consequence may be cell swelling. Thus stimulation of NHE1 and/or NKCC1 by a deviation from homeostasis of a given parameter may regulate that parameter at the expense of compromising others, a coupling that may contribute to irreversible cell damage in a number of pathophysiological conditions. This review addresses the roles of NHE1 and NKCC1 in the cellular responses to physiological and pathophysiological stress. The aim is to provide a comprehensive overview of the mechanisms and consequences of stress-induced stimulation of these transporters with focus on the heart, brain, and blood. The physiological stressors reviewed are metabolic/exercise stress, osmotic stress, and mechanical stress, conditions in which NHE1 and NKCC1 play important physiological roles. With respect to pathophysiology, the focus is on ischemia and severe hypoxia where the roles of NHE1 and NKCC1 have been widely studied yet remain controversial and incompletely elucidated.

Aerobic exercise and lipids and lipoproteins in men: a meta-analysis of randomized controlled trials

BACKGROUND: Aerobic exercise is recommended for improving lipoprotein and lipid levels which at less than their optimal levels are risk factors for cardiovascular disease. Evidence seems lacking for the effectiveness of exercise in reducing these levels, possibly due to small sizes in studies. We concluded a meta-analysis of the studies to examine the effects of aerobic exercise on lipids and lipoproteins in adult men. METHODS: Studies were retrieved via computerized literature searches, cross-referencing from retrieved articles, hand-searching, and expert review of our reference list. Inclusion criteria were randomized controlled trials, aerobic exercise ≥8 weeks, adult men ≥18 years of age, studies published in journal, dissertation, or master's thesis format, studies published in the English-language between January 1, 1955 and January 1, 2003, and assessment of one or more of the following lipids and lipoproteins: total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDLC), and triglycerides (TG). All coding was conducted by both authors, independent of each other. Discrepancies were resolved by consensus. RESULTS: Forty-nine randomized controlled trials representing up to 67 outcomes from 2,990 men (1,741 exercise, 1,249 control) were pooled for analysis. Using random-effects modeling, statistically significant improvements were observed for TC, HDL-C and TG, and a trend for decreases was observed for LDL-C. Changes were equivalent to improvements of 2% for TC and HDL-C, 3% of LDL-C, and 9% for TG. CONCLUSIONS: Aerobic exercise reduces TC and TG and increases HDL-C in men 18 years of age and older.

Erythrocyte membrane ion transport in offspring of hypertensive parents: effect of acute hyperinsulinemia and relation to insulin action

Some patients with essential hypertension exhibit insulin resistance (IR) and several red blood cell (RBC) ion transport abnormalities. The aims of the study were to assess RBC ion transport acitivities under basal conditions, to test in vivo the effect of acute hyperinsulinemia, and to evaluate the relationship to IR in the offspring of hypertensive parents (n = 12; OHP) and healthy controls (n = 14; C). Activities of the Na+-K+ pump, Na+-K+ cotransport, Na+-Li+ countertransport (SLC), and Na+, Rb+, and Li+ leaks (passive membrane permeability) were measured before and after a hyperinsulinemic (75 microU/mL) euglycemic clamp (HIC) and compared to those found under isoinsulinemic isovolumic conditions in OHP and C. An insulin action was calculated as glucose disposal and insulin sensitivity index (M/I) after HIC. OHP were characterized by lower M/I (0.12+/-0.07 vs. 0.20+/-0.09 mg/kg/min/microU/mL; p < 0.05) and elevated SLC and Li+ and Rb+ leaks (p < 0.05) compared with C. Although acute hyperinsulinemia did not modify significantly any ion transport parameter studied, negative correlation was observed between insulin action and membrane cation leaks. Glucose disposal correlated with an Li+ leak in C (r = -0.736; p < 0.01) and all subjects (r = -0.424; p < 0.05) after HIC and in OHP with an Na+ leak (r = -0.727; p < 0.05) before HIC. In conclusion, OHP displayed higher insulin resistance, enhanced activity of SLC, and augmented Li+ and Rb+ leaks. Acute hyperinsulinemia did not modify any ion transport parameter studied, although negative correlation was observed between insulin action and membrane leaks.

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.

Aerobic exercise and resting blood pressure: a meta-analytic review of randomized, controlled trials

In this study the authors used the meta-analytic approach to examine the effects of aerobic exercise on resting systolic and diastolic blood pressure in adults. Forty-seven clinical trials representing a total of 72 effect sizes in 2543 subjects (1653 exercise, 890 control) met the criteria for inclusion. Statistically significant exercise-minus-control decreases were found for changes in resting systolic and diastolic blood pressure in both hypertensive (systolic, -6 mm Hg, 95% CI, -8 to -3; diastolic, -5 mm Hg, 95% CI, -7 to -3) and normotensive (systolic, -2 mm Hg, 95% CI, -3 to -1; diastolic, -1 mm Hg, 95% CI, -2 to -1) groups. The differences between groups were statistically significant (systolic, p=0.008; diastolic, p=0.000). Relative decreases were approximately 4% (systolic) and 5% (diastolic) in hypertensives, and 2% (systolic) and 1% (diastolic) in normotensives. It was concluded that aerobic exercise reduces resting systolic and diastolic blood pressure in adults. (c) 2001 by CHF, Inc.

Exercise training in aging: hemodynamic, metabolic, and oxidative stress evaluations

The effects of exercise training on hemodynamic and metabolic parameters as well as on responses to oxidative stress in aged individuals are controversial. The aim of the present study was to investigate changes in heart hate, mean arterial pressure, vasoreactivity, and plasma levels of insulin and glucose in male aged Wistar rats submitted to exercise training for 11 weeks (1 h/d; 5 d/wk) in a treadmill. The isolated heart was perfused by H2O2, and oxidative stress was evaluated using thiobarbituric acid reactive substances. Cardiovascular functions were recorded with a data acquisition system (CODAS, 1 kHz). Trained aged rats were bradycardic as compared with sedentary aged rats (298+/-7 versus 336+/-16 bpm) but presented similar mean arterial pressure and vasoreactivity and plasma levels of insulin and of glucose, which were quantified by radioimmunoassay and colorimetric enzymatic test. Plasma levels of insulin and of glucose ratio were increased in trained aged rats (6.9+/-0.7 versus 3.5+/-0.4 in sedentary aged rats), and the response to oxidative stress was decreased (0.4+/-0.1 versus 0.7+/-0.1 nmol/mg protein in sedentary aged rats). These results showed that exercise training produced a lower resting heart rate as well as changes in metabolic and oxidative responses. This suggests a higher myocardium protection of trained than sedentary aged rats.

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.

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.

Acute inhibitory effect of alcohol on sodium-lithium countertransport

To assess a possible acute effect of environmental factors on sodium-lithium countertransport (SLC), we determined the activity of this transport system in 14 healthy volunteers, who are nonhabitual drinkers, before and 1 hour after intake of alcohol (0.8g/kg) with "Coke" as the vehicle. Alcohol significantly increased the "leak pathway" component of lithium efflux from a baseline value of 0.21 +/- 0.02 to 0.24 +/- 0.02 mmol/Lcell.h(p < 0.003); and reduced the Vmax of the transporter (0.38 +/- 0.05 to 0.31 +/- 0.04mmol/Lcell.h;p < 0.0005) without significantly changing its affinity for external sodium. The reduction in Vmax was dependent on the initial activity of the transporter (r2 = 0.5). A plot of reduction in Vmax against the product of initial Vmax value and blood alcohol level in each subject revealed a stronger relationship (r2 = 0.86), suggesting that the observed change in Vmax was also dependent on blood alcohol level. Coke alone did not change any of the parameters. We conclude that alcohol acutely inhibits SLC as well as alters erythrocyte membrane in a manner that increases passive lithium efflux.

Sodium-lithium countertransport activity is decreased after weight loss in healthy obese men

Maximal red blood cell (RBC) sodium-lithium countertransport activity has been consistently related to essential hypertension and may be a marker for risk of developing hypertension. Although there is strong evidence for genetic control of sodium-lithium countertransport, increasing evidence suggests that obesity and insulin-glucose metabolism are related to countertransport activity. This study was performed to determine whether countertransport activity decreases with weight loss in healthy obese adults. Forty-five healthy, white, obese adults were studied at baseline and after 6 months of behavioral dietary intervention. Weight loss was 11.5 kg (25.4 lb) in 24 men and 8.1 kg (17.8 lb) in 21 women. Sodium-lithium countertransport activity decreased 55.0 mumol Li/L RBC/h in men (P < .001, paired t test) and 14.6 mumol Li/L RBC/h in women (NS). Change in countertransport activity was correlated with change in body mass index (BMI) in men (r = .52, P < .01) and women (r = .27, NS) and was also strongly correlated with change in fasting glucose levels in both men and women (r = .50 and r = .56, respectively; P < .01) and with change in fasting insulin levels in men (r = .42, P = .04). Change in countertransport activity was not significantly related to change in physical exercise or serum lipid levels. There was a large decrease in systolic blood pressure in men (10.0 mm Hg, P < .001) and a smaller decrease in women (4.1 mm Hg, P < .05). These changes were significantly correlated with change in weight, but not with change in countertransport or baseline countertransport activity.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

Hypertension and exercise. Where do we stand?

Several risk factors have been identified in patients with essential hypertension. The question is whether regular exercise programs can either prevent or alleviate elevated blood pressure. Published studies generally indicate that aerobic exercise of large-muscle groups can be used as an interventional regimen for hypertension. For mild hypertension, moderate-intensity walking is recommended at least three times a week. Improvement may not be evident in less than 6 months. When exercise alone is not effective or when hypertension is more severe, exercise can still be used as an adjunct to pharmacologic therapy.

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.

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)

Effects of endurance training on baroreflex sensitivity and blood pressure in borderline hypertension

Physical training offers a potential nonpharmacological strategy for control of mild and borderline hypertension, but its effect on blood pressure is controversial. We investigated the effects of endurance training on waking and sleeping blood pressure and on baroreflex sensitivity in 16 borderline hypertensive patients. First, 8 patients were assessed before and after a 6-month endurance training programme. Then, when it was clear that blood pressures were lower after training, a further 8 patients were studied not only at the end of the training programme but also after 4 months' abstention from exercise (detraining). Measurements were taken of baroreflex sensitivity (response to iv phenylephrine), blood pressure, R-R interval, and blood pressure and R-R variability. Ambulatory blood pressures were measured in 13 patients (7 trained, 6 detrained) and sleep blood pressures in 6 patients (3 trained, 3 detrained). Increased fitness was associated with a decline in resting arterial blood pressure of 9.7 (SE 2.0) mm Hg systolic and 6.8 (1.2) mm Hg diastolic, and with a decline in ambulatory blood pressure of 4.8 (1.4) mm Hg and 7.5 (2.1) mm Hg, respectively; both p less than 0.05. Baroreflex sensitivity was 14.0 (1.8) ms/mm Hg in the unfit and 17.5 (2.0) ms/mm Hg in the fit; p less than 0.05. Sleep blood pressures were not lower in the fit despite longer sleep R-R intervals. These findings indicate that, in some subjects with borderline or mild hypertension, a physical training programme is sufficient to bring the blood pressure within normal limits.

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.

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.

Increased blood pressure and erythrocyte sodium/lithium countertransport activity are not inherited in diabetic nephropathy

Genetic predisposition to essential hypertension, represented by maximal erythrocyte sodium/lithium countertransport activity, has been suggested as a marker for the risk of developing clinical nephropathy in Type 1 (insulin-dependent) diabetes mellitus. To evaluate this hypothesis we measured arterial blood pressure and maximal sodium/lithium countertransport activity of erythrocytes in 80 parents of 49 Type 1 diabetic patients with clinical nephropathy, 78 parents of 49 normoalbuminuric patients and 17 age-matched non-diabetic individuals. The two diabetic groups were carefully matched. In the two groups of parents blood pressure and cell sodium/lithium countertransport activity showed no significant differences (137/83 vs 133/81 mm Hg and 0.33 vs 0.32 mmol/(1 cells x h) respectively). The proportion of parents who had died or received antihypertensive drugs was similar in the two groups. The patients with Type 1 diabetes had significantly higher sodium/lithium countertransport compared to the 39 non-diabetic control subjects independently of the presence or absence of nephropathy (p less than 0.002). However, patients with nephropathy tended to have higher sodium/lithium countertransport activity than normoalbuminuric patients (0.48 vs 0.41 mmol/(1 cells x h), p = 0.06). We conclude that genetic predispositions to essential hypertension and increased maximal erythrocyte sodium/lithium countertransport activity do not appear to be risk markers for the development of clinical nephropathy in Type 1 diabetic patients.

Diurnal variation of erythrocyte sodium-lithium countertransport rate and intracellular cation concentrations

Differences in erythrocyte sodium-lithium countertransport rate and erythrocyte potassium concentration were found between 0900 h and 2100 h in ten healthy individuals. Sodium-lithium countertransport rates were lowest at 0900 h (x: 0.34 mmol/l per h; SD: 0.15) and highest at 1200 h (x: 0.42 mmol/l per h; SD: 0.16). Erythrocyte potassium concentrations increased progressively during the day, while erythrocyte sodium concentrations did not change significantly during the day. For comparative and epidemiological studies of erythrocyte sodium-lithium countertransport rate blood samples should be taken at the same time of the day.

Membrane transport of ions in hypertension

A variety of disturbances in transmembrane monovalent and divalent cation fluxes has been described in blood cells from hypertensive patients. Other membrane properties, such as fluidity and calcium binding, are also altered. It is now abundantly clear that some of the inconsistencies in this field are due to poor matching of patients and controls. However, even when careful matching is carried out, differences in membrane functions are still seen. It is suggested that these are due to a disturbance in the physicochemical properties of the cell membrane, related to changes in cell membrane phospholipid fluidity. This change could maintain peripheral resistance either by directly or indirectly increasing tone or by predisposing to resistance vessel hypertrophy. Recent evidence emphasizes the role of the latter rather than the former in experimental hypertension. It is postulated that overactivity of the phosphoinositide second messenger system as a result of alteration in all membrane properties predisposes genetically susceptible individuals to resistance-vessel hypertrophy and hypertension.

Changes in sodium-lithium countertransport correlate with changes in triglyceride levels and body mass index over 2 1/2 years of follow-up in Utah

We have previously reported from a cross-sectional study that plasma total cholesterol, triglycerides, and HDL-C were significantly and independently correlated with Na(+)-Li+ countertransport. These original participants were rescreened 2 1/2 years later (range of 20-58 months), with lipid, blood pressure, and Na(+)-Li+ countertransport measurements from both visits on 906 normotensive adults. The correlation found between age- and sex-adjusted triglyceride levels and Na(+)-Li+ countertransport at visit 1 (r = 0.34, p less than 0.0001) was reconfirmed at visit 2 (r = 0.32, p less than 0.0001). The Na(+)-Li+ countertransport correlations with HDL-C (r = -0.11, p less than 0.01) and body mass index (r = 0.24, p less than 0.0001) also remained at visit 2. After 30 months, there were significant increases of triglyceride, body mass index, blood pressure, and Na(+)-Li+ countertransport levels, and significant decreases of HDL-C and total cholesterol levels, after adjusting the changes in these variables between visit 2 and visit 1 for age, sex, time between the two visits, and the visit 1 level of the variable. Increases in triglycerides, cholesterol, and body mass index were significantly correlated with increases in Na(+)-Li+ countertransport (r = 0.23, r = 0.19, and r = 0.21, respectively). The correlations of the lipid and lipoprotein changes with Na(+)-Li+ countertransport changes were independent of body mass index and blood pressure changes. We conclude that increasing plasma triglyceride levels and body mass index are associated with increasing Na(+)-Li+ countertransport levels in both cross-sectional and longitudinal data.

Apolipoprotein, low density lipoprotein subfraction, and insulin associations with familial combined hyperlipidemia. Study of Utah patients with familial dyslipidemic hypertension

Familial dyslipidemic hypertension (FDH) is a syndrome recently described from sibships selected for early familial hypertension and found to have one or more of three fasting lipid abnormalities [high triglycerides, low high density lipoprotein (HDL) cholesterol, high low density lipoprotein (LDL) cholesterol]. In further analyses of these same 131 hypertensive subjects, apolipoprotein A-I and B, fasting plasma insulin (adjusted for body mass index), and detailed anthropometrics were different in two subgroups of FDH. Of 63 FDH patients, 19 met the criteria for familial combined hyperlipidemia (FCHL); 44 did not, but still had high triglyceride and/or low HDL cholesterol levels. When compared to 20 normolipidemic hypertensive patients, the 19 hypertensive patients with FCHL had 196% higher very low density lipoprotein cholesterol (p = 0.0001), 33% higher apolipoprotein B (p = 0.0002), smaller LDL particles (p = 0.007), and 73% higher fasting insulin (p = 0.003), but no significant differences in body mass index or skinfold thicknesses. The other 44 FDH patients without FCHL had 33% lower HDL (p = 0.0001), with only 8% lower apolipoprotein A-I levels (p = 0.20); significantly higher subscapular skinfolds (p = 0.02), weights (p = 0.002), body mass index (p = 0.006), knee widths (p = 0.0007), and wrist circumferences (p = 0.0009); smaller, denser LDL subfractions (p = 0.001); and increased apolipoprotein B levels (p = 0.01) compared to the normolipidemic hypertensive group. Increased fasting insulin levels were similar to the normolipidemic group and significantly lower than the FCHL group after adjustment for body mass index, suggesting a relationship between obesity and fasting insulin levels only in the non-FCHL group. We conclude that FDH consists of at least two subgroups: 1) FCHL with high apolipoprotein B, small LDL particles, and increased fasting plasma insulin levels, and 2) a less well-defined residual having upper central obesity with low HDL cholesterol and high triglyceride levels. Elevated insulin levels found in both groups, but possibly originating through different physiological mechanisms, may provide the pathophysiological connections between dyslipidemia, obesity, and hypertension.

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.

Sympathetic nervous function and erythrocyte cation transport systems in normotensive individuals with family history of hypertension

To investigate the influence of heredity to the sympathetic nervous function and the cell membrane cation transport systems, we studied the blood pressure and plasma catecholamine response to supine exercise testings by bicycle ergometer, the pressure response to noradrenaline infusion tests and the heart rate response to isoproterenol infusion tests in 88 healthy Japanese sedentary normotensive men with and without a family history of essential hypertension [FHH(+) and FHH(-)]. Several erythrocyte monovalent cation transport parameters were also measured in 74 of these individuals. In the results, (1) the systolic blood pressure response to exercise testings and noradrenaline infusion tests were larger in FHH(+) than FHH(-): (2) there was no difference between FHH(+) and FHH(-) in the heart rate response to isoproterenol infusion tests: (3) there was no significant difference between FHH(+) and FHH(-) in the increased plasma catecholamine levels to exercise testings: (4) the intraerythrocytic sodium content was significantly higher in FHH(+) than in FHH(-): and (5) several erythrocyte monovalent cation transport systems (Li-Na countertransport, Na-K cotransport and Na-K pump activity) were clearly accelerated in FHH(+). We concluded that in spite of normotension there were abnormalities of sympathetic nervous function, intracellular sodium content and several cell membrane cation transport systems in individuals with a family history of essential hypertension.

Elevated intracellular Ca2+ affects Lii-Nao countertransport in human red blood cells

Changes in cytoplasmic Ca2+ concentration and in Lii-Nao countertransport activity have been shown to be associated with essential hypertension. Elevated intracellular free [Ca2+], as well as abnormalities of Ca2+ binding and transport have been reported in cells from different tissues of hypertensive laboratory animals and essential hypertensive patients. Similarly, enhanced rates of Lii-Nao countertransport and the modified pattern of the temperature dependence of this activity in red blood cells from essential hypertensive patients have been previously demonstrated. The aim of the present study was to investigate possible interaction between changes in intracellular free [Ca2+] and the Lii-Nao exchange in human red blood cells. The ionophore ionomycin was used to allow Ca2+ incorporation into the cells in a dose-dependent manner. The elevation of intracellular [Ca2+], in turn, resulted in enhanced Li+ efflux from the cells. At 3 microM, ionomycin selectively and significantly enhanced the Lii-Nao countertransport but not Li+ leakage from the cells. EGTA totally abolished the effect of ionomycin, indicating that the effect is directly related to Ca2+. As low as 0.4 microM Ca2+ caused a statistically significant effect. The maximal effect of Ca2+ on the Lii-Nao countertransport was achieved around the external pH range of 6.8-7.5. In contrast, the leakage of Li+ was significantly enhanced by Ca2+ at a pH of 7.4 and above. Ca2+ did not affect the Km of the Lii-Nao countertransport for Li+. Amiloride, which inhibits Na+/H+ exchange, inhibited only 10% of the Ca2+-enhanced countertransport. It is concluded that Ca2+ may play a role in the regulation of Lii-Nao countertransport in erythrocytes.

The Li+-Na+ exchange and Na+-K+-Cl- cotransport systems in essential hypertension

This review examines the physiological functions of the Li+-Na+ exchanger and Na+-K+-Cl- cotransport system in human red blood cells. Both transporters are family aggregated and determined mainly by genetic factors; they are present in kidney and vascular cells, where they are regulated by vasoactive substances. To assess the physiological function of these two transporters, we investigated their kinetic and equilibrium properties, and their modulation by vasoactive substances. Recent studies in red blood cells indicate that the Li+-Na+ exchanger may be a mode of operation of the Na+-H+ exchanger, which plays an important role in the regulation of cell pH, cell volume, and transtubular sodium transport. In vascular cells, Na+-H+ exchanger is modulated by vasoconstrictors such as growth factors and angiotensin, while Na+-K+-Cl- cotransport is modulated by vasodilators such as atrial natriuretic factor and bradykinin. Kinetic studies in red blood cells of hypertensive patients and their offspring indicate the presence of subsets with elevated Vmax of Li+-Na+ exchange or high Km for cell sodium for outward Na+-K+-Cl- cotransport. The latter alteration is found most frequently in young blacks born of hypertensive parents, and it appears to be dependent on their level of sodium intake. The relationship between the alterations of the red blood cell sodium exchanger and Na+-K+-Cl- cotransport and risk factors for hypertension indicates that they can provide a tool to examine the interaction of genetic, hormonal, and environmental factors in human hypertension.

Membrane polyunsaturated fatty acids and lithium-sodium countertransport in human erythrocytes

Two groups of individuals, 26 normotensive normolipemic and 37 normotensive hyperlipemic, all without family history of hypertension have been selected in attempt to demonstrate whether Li-Na countertransport of erythrocytes is influenced by plasma and membrane lipid composition. The maximal rate of Li-Na countertransport was elevated in hyperlipemics (0.344 +/- 0.168 vs 0.220 +/- 0.074 mmol/l erythrocytes/h). This difference is highly significant. Hyperlipemics had different composition of membrane lipids than normals. The most important variations were: increase of palmitic, palmitoleic and total saturated fatty acids (SFA) as well as increase of cholesterol/phospholipids ratio (C/PL); in contrast, hyperlipemics had a reduced amount of linoleic acid and total unsaturated fatty acids (UFA) as well as total polyunsaturated fatty acids (PUFA). Consequently, UFA/SFA and PUFA/SFA ratios were lower than in normals. Li-Na countertransport was negatively correlated with the amount of PUFA (P less than 0.02), whereas it was positively correlated with the following parameters: oleic/linoleic ratio (p less than 0.02), monounsaturated fatty acids/polyunsaturated fatty acids ratio (p less than 0.03) as well as with the SFA + monounsaturated fatty acid/PUFA ratio (p less than 0.03). These findings suggest that the V max of Li-Na countertransport in erythrocytes is influenced by the lipid composition of the membrane.

Red blood cell Li+-Na+ countertransport, Na+-K+ cotransport, and the hemodynamics of hypertension

Red blood cell Li+-Na+ countertransport and Na+-K+ cotransport activities, home blood pressure, invasive systemic hemodynamics, and limb venous compliance were measured in 65 white men (23 normotensive, 22 borderline hypertensive, and 20 mild essential hypertensive subjects). Li+-Na+ countertransport activity was positively and significantly correlated with subject-determined home systolic blood pressure (r = 0.31, p less than 0.02) and with directly measured systolic (r = 0.29, p less than 0.02) and diastolic (r = 0.27, p less than 0.03) blood pressures in the hemodynamic laboratory, independent of potential confounding variables. Analysis of the hemodynamic determinants of blood pressure revealed a significant positive correlation of countertransport with vascular resistance (r = 0.30, p less than 0.02) but not with cardiac output or cardiac index. High red blood cell Na+-K+ cotransport activity was not independently associated with hypertension or with a characteristic hemodynamic pattern but was related to decreased venous compliance. Red blood cell Li+-Na+ countertransport deserves further study as a marker for the genetic substrate of human essential hypertension. Red cell Na+-K+ cotransport may be altered secondarily by factors related to high blood pressure and seems to be a valid marker for abnormalities of the venous system in hypertension.

Effect of cold pressor test-induced stress on leukocyte sodium transport and norepinephrine

The effects of stress on leukocyte membrane sodium efflux rate constant and plasma norepinephrine levels were studied before and during cold pressor test in normotensive subjects with and without a family history of hypertension. After 20 minutes of supine rest, no significant differences in total, ouabain-resistant or ouabain-sensitive sodium efflux rate constants were apparent between the two groups. In normotensive subjects with no family history, there was no significant change in any efflux rate constant during cold pressor test, although there was a highly significant negative correlation between change in total efflux rate constant and change in norepinephrine levels (r = -0.82, p less than 0.01, n = 12). During cold pressor test in subjects with a family history of hypertension, there was a significant rise in the ouabain-resistant efflux rate constant (1.5 +/- 0.1 vs 1.0 +/- 0.1 hr-1; p less than 0.01, n = 10); this level was also significantly higher than that in control subjects (p less than 0.002). In this group, the ouabain-sensitive efflux rate constant fell slightly but not significantly (1.8 +/- 0.2 vs 2.1 +/- 0.2 hr-1; n = 10). These results suggest that stress in the form of a cold stimulus produces qualitative differences in leukocyte cation transport in normotensive offspring of hypertensive patients as compared with subjects without such a family history.

Associations of three erythrocyte cation transport systems with plasma lipids in Utah subjects

To investigate the pathophysiology of essential hypertension, detailed biochemical and clinical variables were collected and analyzed for 2091 Utah subjects aged 3 to 83 years. Three different measurements of erythrocyte cation transport were obtained: Na+-Li+ countertransport, Li+-K+ cotransport, and furosemide-insensitive Li+ efflux into MgCl2. Total plasma cholesterol, triglycerides, and high density lipoprotein cholesterol levels were obtained from fasting subjects. Levels of high density lipoprotein subfractions 2 and 3 were also obtained from 350 subjects. Standardized data collection also included blood pressure, height, weight, and presence or absence of a diagnosis or treatment of essential hypertension. In univariate analyses of all 1420 adults, each of the three transport systems showed the same significant correlations with triglyceride levels (r = 0.33-0.35, p less than 0.0001), high density lipoprotein concentration (r = -0.19 to -0.21, p less than 0.001), and weight (r = 0.22-0.28, p less than 0.0001). In multivariate regression analyses, values for each transport system were significantly higher in hypertensive subjects; values for triglycerides, high density lipoprotein, and usually, the high density lipoprotein subfractions continued to have strong significant independent associations with all three transport systems; and weight remained significantly related only to Na+-Li+ countertransport. In separate logistic regressions, plasma triglyceride levels (positively, p less than 0.001) and high density lipoprotein subfraction 3 levels (inversely, p less than 0.03) were associated with hypertension itself. In multivariate analyses among 671 children, high density lipoprotein and high density lipoprotein subfraction 3 levels showed significant (p less than 0.05) inverse correlations with Na+-Li+ countertransport and furosemide-insensitive Li+ efflux.(ABSTRACT TRUNCATED AT 250 WORDS)