Lymphocyte membrane sodium-proton exchange in spontaneously hypertensive rats

“Greedy Organs Hypothesis” for sugar and salt in the pathophysiology of non-communicable diseases in relation to sodium-glucose co-transporters in the intestines and the kidney

Deposition of visceral fat and insulin resistance play central role in the development of non-communicable diseases (NCDs) including obesity, hypertension and type 2 diabetes. However, we shed more light upon the intestines and the kidney as a strong driver of NCDs. Based upon unexpected outcomes of clinical trials using sodium-glucose cotransporter (SGLT) 2 inhibitors to demonstrate their actions for not only body weight reduction and blood glucose fall but also remarkable cardiorenal protection, we speculate that hyperfunction of the intestines and the kidney is one of critical contributing factors for initiation of NCDs. By detecting high amount of glucose and sodium chloride around them by sweet/salt taste sensors, the intestines and the kidney are designed to (re)absorb these nutrients by up-regulating SGLT1 or SGLT2. We designate these hyperfunctioning organs for nutrient uptake as “greedy organs”. The greedy organs can induce NCDs (“greedy organ hypothesis”). SGLTs are regulated by glucose and sodium chloride, and SGLTs or other genes can be “greedy genes.” Regulating factors for greedy organs are renin-angiotensin system, renal sympathetic nervous activity, gut inflammation/microbiota or oxidative stress. Mitigation of organ greediness by SGLT2 inhibitors, ketone bodies, bariatric surgery, and regular lifestyle to keep rhythmicity of biological clock are promising.

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We propose the concept of “Greedy Organs” hypothesis as a possible cause of NCDs.

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Clinical implication of greedy kidney is supported by the effect of SGLT2 inhibitors.

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The significance of greedy intestines is suggested by the effect of bariatric surgery.

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The intestines and kidney become hyperactive through upregulation of SGLT1 or 2.

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To mitigate “greedy organs” should be a promising strategy against NCDs.

Effect of different antihypertensive treatments on Ras, MAPK and Akt activation in hypertension and diabetes

Ras GTPases function as transducers of extracellular signals regulating many cell functions, and they appear to be involved in the development of hypertension. In the present study, we have investigated whether antihypertensive treatment with ARBs (angiotensin II receptor blockers), ACEi (angiotensin-converting enzyme inhibitors) and diuretics induce changes in Ras activation and in some of its effectors [ERK (extracellular-signal-regulated kinase) and Akt] in lymphocytes from patients with hypertension without or with diabetes. ACEi treatment transiently reduced Ras activation in the first month of treatment, but diuretics induced a sustained increase in Ras activation throughout the 3 months of the study. In patients with hypertension and diabetes, ARB, ACEi and diuretic treatment increased Ras activation only during the first week. ACEi treatment increased phospho-ERK expression during the first week and also in the last 2 months of the study; however, diuretic treatment reduced phospho-ERK expression during the last 2 months of the study. In patients with hypertension and diabetes, antihypertensive treatments did not induce changes in phospho-ERK expression in lymphocytes. ACEi treatment reduced phospho-Akt expression in patients with hypertension and diabetes only in the first month of treatment. In conclusion, these findings show that antihypertensive treatments with ACEi, and diuretics to a lesser extent, modify Ras activation and some of its signalling pathways, although in different directions, whereas ARBs do not appear to have any influence on Ras signalling pathways.

Adverse interactions of rofecoxib with lisinopril in spontaneously hypertensive rats

BACKGROUND

Hypertension and arthritis are frequent comorbidities. Nonsteroidal anti-inflammatory drugs (NSAIDs) are well known to produce hypertension or attenuate the effects of antihypertensive agents in a few patients. The influence of selective NSAIDs on blood pressure and the cardiovascular and renal effects of coxibs have still to be investigated. The purpose of this study was to test the hypothesis that rofecoxib interferes with antihypertensive activity and cardiorenal protective effects of lisinopril in spontaneously hypertensive rats (SHRs).

METHODS

Twenty-one unanaesthetised, male spontaneously hypertensive rats (SHRs), 16 weeks old, were randomized to receive lisinopril (LS) 15 mg/kg/d or rofecoxib (RF) 20 mg/kg/d or combination of lisinopril (LS) and rofecoxib (RF) for 2 weeks. The arterial blood pressure changes were recorded each week. The Sodium Hydrogen Exchange (NHE) activity of erythrocytes was determined 2 weeks after the study. The surviving animals were sacrificed 24 h after the last dose, and the sections of their hearts and kidneys were assessed histologically for injury by a pathologist masked to the treatment.

RESULTS

RF completely prevented the hypotensive effects of LS during the first week of treatment but the antihypertensive efficacy of LS was restored during the second week of treatment. The NHE in erythrocytes of 18-week-old SHRs was found to be significantly lower than the age-matched Wistar rats (P < 0.05), and LS treatment reversed these values to Wistar control in SHRs. RF was devoid of any effect on NHE of erythrocytes. The histological examination revealed that the myocardial and renal protection induced by LS was attenuated by concomitant RF therapy.

CONCLUSIONS

These results indicate that COX-2 inhibitors should be used judiciously in patients with history of hypertension, ischemic heart disease, or chronic renal failure.

The mechanism of action of angiotensin II is dependent on direct activation of vascular smooth muscle carbonic anhydrase I

Our previous studies have shown that angiotensin II increases carbonic anhydrase activity both in vitro and in vivo. In this study we investigated in vitro the effect of angiotensin II on carbonic anhydrase I and II from erythrocytes and on arteriolar vascular smooth muscle carbonic anhydrase I. We also studied in vitro and in vivo the effect of angiotensin II receptor blockers (irbesartan and candesartan) on purified carbonic anhydrase I and II, on vascular smooth muscle carbonic anhydrase I and on arterial blood pressure in humans and in animals. In vitro results showed that angiotensin II is a direct and stronger activator of carbonic anhydrase I than II. Angiotensin II receptor blockers reduced mainly carbonic anhydrase I activity and completely antagonized the activating effect of angiotensin II both on purified and on vascular smooth muscle carbonic anhydrase I. Our in vivo experiments showed that irbesartan and candesartan are powerful inhibitors of carbonic anhydrase I both in erythrocytes (in humans) and in vascular smooth muscles (in animals). In humans, irbesartan and candesartan progressively reduce arterial blood pressure in hypertensive subjects, in parallel with progressive reduction of erythrocyte carbonic anhydrase I activity. We believe that angiotensin II could have a dual mechanism of action: (1) angiotensin interacting with its receptor to form a stimulus-receptor complex; (2) the same stimulus directly acts on the carbonic anhydrase I isozyme (which might be coupled with angiotensin II receptors), ensuring an adequate pH for stimulus-receptor coupling for signal transmission into the cell and hence vasoconstriction.

Catecholamine-induced vasoconstriction is sensitive to carbonic anhydrase I activation

We studied the relationship between alpha- and beta-adrenergic agonists and the activity of carbonic anhydrase I and II in erythrocyte, clinical and vessel studies. Kinetic studies were performed. Adrenergic agonists increased erythrocyte carbonic anhydrase as follows: adrenaline by 75%, noradrenaline by 68%, isoprenaline by 55%, and orciprenaline by 62%. The kinetic data indicated a non-competitive mechanism of action. In clinical studies carbonic anhydrase I from erythrocytes increased by 87% after noradrenaline administration, by 71% after orciprenaline and by 82% after isoprenaline. The increase in carbonic anhydrase I paralleled the increase in blood pressure. Similar results were obtained in vessel studies on piglet vascular smooth muscle. We believe that adrenergic agonists may have a dual mechanism of action: the first one consists of a catecholamine action on its receptor with the formation of a stimulus-receptor complex. The second mechanism proposed completes the first one. By this second component of the mechanism, the same stimulus directly acts on the carbonic anhydrase I isozyme (that might be functionally coupled with adrenergic receptors), so that its activation ensures an adequate pH for stimulus-receptor coupling for signal transduction into the cell, resulting in vasoconstriction.

Increases in intracellular calcium of arterial smooth muscle cells in transgenic mice overexpressing Na+/H+ exchanger

We produced transgenic mice overexpressing Na+/ H+ exchanger as a model of salt-sensitive hypertension and reported that dietary salt loading elevates blood pressure in these transgenic mice. We speculate that this blood pressure elevation may be attributed to the elevation of intraarterial smooth muscle Ca2+ concentration through Na+/Ca2+ exchange. To test this hypothesis, we measured the isometric tension of aortic rings and intracellular free calcium ([Ca2+]i) of cultured smooth muscle cells. In the transgenic mice, the aortic ring contraction induced by 5 mM caffeine (percentage of 60 mM K-induced contraction) was significantly greater than control mice (60.1 +/- 5.5% vs. 44.8 +/- 3.1%). The mean [Ca2+]i in vascular smooth muscle cells (VSMCs) of transgenic mice (123.1 +/- 19.7 nM) was higher than those in VSMCs of control mice (66.6 +/- 7.2 nM). These observations suggest that dietary salt loading increases the concentration of calcium in arterial smooth muscle cells in this transgenic mice. These findings are helpful in tracing the causes of salt-sensitive hypertension.

Genetic and biochemical determinants of abnormal monovalent ion transport in primary hypertension

Data obtained during the last two decades show that spontaneously hypertensive rats, an acceptable experimental model of primary human hypertension, possess increased activity of both ubiquitous and renal cell-specific isoforms of the Na+/H+ exchanger (NHE) and Na+-K+-2Cl- cotransporter. Abnormalities of these ion transporters have been found in patients suffering from essential hypertension. Recent genetic studies demonstrate that genes encoding the beta- and gamma-subunits of ENaC, a renal cell-specific isoform of the Na+-K+-2Cl- cotransporter, and alpha3-, alpha1-, and beta2-subunits of the Na+-K+ pump are localized within quantitative trait loci (QTL) for elevated blood pressure as well as for enhanced heart-to-body weight ratio, proteinuria, phosphate excretion, and stroke latency. On the basis of the homology of genome maps, several other genes encoding these transporters, as well as the Na+/H+ exchanger and Na+-K+-2Cl- cotransporter, can be predicted in QTL related to the pathogenesis of hypertension. However, despite their location within QTL, analysis of cDNA structure did not reveal any mutation in the coding region of the above-listed transporters in primary hypertension, with the exception of G276L substitution in the alpha1-Na+-K+ pump from Dahl salt-sensitive rats and a higher occurrence of T594M mutation of beta-ENaC in the black population with essential hypertension. These results suggest that, in contrast to Mendelian forms of hypertension, the altered activity of monovalent ion transporters in primary hypertension is caused by abnormalities of systems involved in the regulation of their expression and/or function. Further analysis of QTL in F2 hybrids of normotensive and hypertensive rats and in affected sibling pairs will allow mapping of genes causing abnormalities of these regulatory pathways.

Functional significance of cell volume regulatory mechanisms

To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.

A 90-kD Na(+)-H+ exchanger kinase has increased activity in spontaneously hypertensive rat vascular smooth muscle cells

Increased activity of the Na(+)-H+ exchanger (NHE-1 isoform) has been observed in cells and tissues from hypertensive humans and animals, including the spontaneously hypertensive rat (SHR). No mutation in NHE-1 DNA sequence or alteration in NHE-1 mRNA and protein expression has been demonstrated in hypertension, indicating that alterations in proteins that regulate NHE-1 activity are responsible for increased activity. The recent finding that NHE-1 phosphorylation in SHR vascular smooth muscle cells (VSMCs) was greater than in Wistar-Kyoto rat (WKY) VSMCs suggested that NHE-1 kinases may represent an abnormal regulatory pathway present in hypertension. To define NHE-1 kinases altered in the hypertensive phenotype. We measured NHE-1 kinase activity by an in-gel-kinase assay using a recombinant glutathione S-transferase NHE-1 fusion protein as a substrate. At least 7 NHE-1 kinases (42 to 90 kD) were present in VSMCs. We studied a 90-kD kinase because it was the major NHE-1 kinase and exhibited differences between SHR and WKY. Comparison of 90-kD kinase activity revealed that SHR VSMCs had increased activity in growth-arrested cells and in cells stimulated by angiotensin II (100 nmol/L for 5 minutes). Activation of the 90-kD kinase by angiotensin II was Ca2+ dependent, PKC independent, and partially dependent on the mitogen-activated protein kinase pathway. These findings indicate that increased activity of a 90-kD NHE-1 kinase is a characteristic of SHR VSMCs in culture and suggest that alterations in the 90-kD NHE-1 kinase and/or proteins that regulate its activity may be a pathogenic component in hypertension in the SHR.

Chelerythrine inhibits Na(+)-H+ exchange in platelets from spontaneously hypertensive rats

Hypertension has been associated with increased activity of the Na(+)-H+ exchanger. To study the role played by protein kinase C in this process, we used chelerythrine, a potent and specific inhibitor of the kinase. After an acid load by ammonium chloride preincubation, platelets isolated from spontaneously hypertensive rats showed a faster and larger increase in intracellular pH than platelets from Wistar-Kyoto rats. The initial rate of intracellular pH recovery was 2.46 +/- 0.26 pH units per minute in spontaneously hypertensive rats and 1.74 +/- 0.19 in Wistar-Kyoto rats. For protein kinase C inhibition, platelets were incubated for 30 minutes with 10 mumol/L chelerythrine. This treatment induced a significant reduction in the recovery rate only in spontaneously hypertensive rat platelets, indicating that a pathway involving protein kinase C participates in the prestimulation of the exchanger in cells from this rat strain. Addition of chelerythrine reduced the baseline intracellular pH of platelets. No significant difference was found between the decrease of steady-state intracellular pH induced by chelerythrine in either rat strain. These findings indicate that this model of hypertension is characterized by increased Na(+)-H+ activity mediated by protein kinase C stimulation.

Enhanced Na(+)-H+ exchanger activity and NHE-1 mRNA expression in lymphocytes from patients with essential hypertension

It has been demonstrated that the activity of the sodium-proton exchanger (NHE-1 isoform) is increased in lymphocytes and other blood cells from patients with essential hypertension. In the present study, we investigated whether an increased level of NHE-1-specific mRNA in lymphocytes from patients with essential hypertension would explain the enhanced transport activity. Twenty-two hypertensive patients and 21 normotensive subjects were studied. Basal cytosolic pH was measured by the pH-sensitive fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Maximal sodium-proton exchange activity was determined by acidifying cell pH and measuring the initial rate of the net sodium-dependent proton efflux driven by an outward proton gradient. The transcript level of NHE-1 was measured by reverse transcription-polymerase chain reaction in comparison with a constitutively expressed reference gene (beta-actin). Intracellular pH was lower in hypertensive patients than normotensive subjects (7.34 +/- 0.01 versus 7.39 +/- 0.01, mean +/- SEM, P < .001). The maximal activity of the sodium-proton exchanger was higher in hypertensive patients than in normotensive subjects (1262 +/- 100 versus 881 +/- 56 mmol/L cells per hour, P < .01). NHE-1 mRNA was increased in hypertensive patients compared with normotensive subjects (ratio of NHE-1 mRNA to beta-actin mRNA, 0.16 +/- 0.01 versus 0.12 +/- 0.02, P < .05). These data suggest that the increased sodium-proton exchange activity in essential hypertension may be related to the de novo synthesis of exchanger protein.

Kinetics of Na+/H+ exchange in vascular smooth muscle cells from WKY and SHR: effects of phorbol ester

The kinetic properties of Na+/H+ exchange were investigated in vascular smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity was measured in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were performed without (control) and with pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differed between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (Vmax) values (55.85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+.l-1.min-1) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WKY VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting Vmax (31.88 +/- 1.55 mmol H+.l-1.min-1). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport activity in VSMC from SHR compared with WKY, i.e., increased Vmax and decreased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked degree of antiporter prestimulation in this animal model of genetic hypertension.

Salt-sensitive hypertension in transgenic mice overexpressing Na(+)-proton exchanger

Essential hypertension is one of the most common diseases that exacerbate the risk of cardiovascular or cerebrovascular attacks. Although the etiology of essential hypertension remains unclear, recent investigations have revealed that an enhancement of Na(+)-proton (Na(+)-H+) exchange activity is a frequently observed ion transport abnormality in hypertensive patients and animal models. To test the hypothesis that increased Na(+)-H+ exchange causes hypertension, we produced transgenic mice overexpressing Na(+)-H+ exchanger and analyzed their Na+ metabolism and blood pressure. Urinary excretion of water and Na+ was significantly decreased in transgenic mice, and systolic blood pressure was elevated after salt loading. The impaired urinary excretion of Na+ suggested that the Na(+)-H+ exchanger overexpressed in the renal tubules increased reabsorption of Na+, which caused a blood pressure elevation by Na+ retention after excessive salt intake. Our results demonstrate that overexpression of Na(+)-H+ exchanger can be a genetic factor that interacts with excessive salt intake and causes salt-sensitive blood pressure elevation.

Na(+)-H+ exchanger expression in vascular smooth muscle of spontaneously hypertensive and Wistar-Kyoto rats

The Na(+)-H+ exchanger has important modulatory effects on vascular smooth muscle cell proliferation and contractility. Increased Na(+)-H+ exchange activity is a general property of many tissues, including mesenteric artery and cultured vascular smooth muscle cells, in the spontaneously hypertensive rat (SHR). In the present work, we investigated whether alterations in the steady-state levels of specific Na(+)-H+ exchanger mRNA isoforms (NHE-1 through NHE-4) are associated with the observed increases in exchanger activity. Poly(A+) mRNA prepared from 12-week-old hypertensive SHR and normotensive Wistar-Kyoto (WKY) aorta, kidney, and intestine was hybridized to cDNAs specific for each NHE isoform. By Northern blot analysis, NHE-1 was detected in all tissues as well as cultured vascular smooth muscle cells and was not regulated differently in SHR compared with WKY tissues. There was no expression of NHE-2, NHE-3, or NHE-4 in SHR and WKY aortas or in cultured vascular smooth muscle cells from SHR and WKY aortas. Stimulation of NHE-1 mRNA expression by growth factors was similar in cultured SHR and WKY vascular smooth muscle cells. We conclude that the previously observed increase in exchanger activity in blood vessels and cultured vascular smooth muscle cells of the SHR is not caused by induction of the NHE-2, NHE-3, and NHE-4 isoforms or by alterations in steady-state NHE-1 mRNA expression. These findings suggest that posttranslational regulation of the Na(+)-H+ exchanger is responsible for increased activity in the SHR.

Sodium-proton (Na+/H+) exchange inhibition increases blood pressure in spontaneously hypertensive rat

The current study was designed to determine the role of sodium-proton (Na+/H+) exchange in blood pressure regulation in sodium chloride (NaCl)-sensitive and NaCl-resistant spontaneously hypertensive rats and control Wistar-Kyoto rats (WKY) using 5-(N,N-hexamethylene)amiloride (HMA), a potent and selective inhibitor of Na+/H+ exchange. The response of mean arterial pressure to intravenous infusion of HMA was examined in conscious, unrestrained male rats maintained on normal (1%) or high (8%) NaCl diets for 3 weeks beginning at age 7 weeks. The HMA significantly increased mean arterial pressure in NaCl-sensitive spontaneously hypertensive rats and NaCl-resistant spontaneously hypertensive rats that were fed 1% NaCl, but not in WKY rats that were fed 1% NaCl; the 8% NaCl diet enhanced this pressor response in all 3 strains. The pressor response was accompanied by significant increases in plasma norepinephrine levels in NaCl-sensitive spontaneously hypertensive rats on both diets, but not in NaCl-resistant spontaneously hypertensive rats or WKY rats on either diet. There were no differences in steady-state levels (30-60 nM) of plasma HMA between diet groups in any strain. Therefore, administration of HMA in a dose at which it is highly selective for the Na+/H+ exchanger (Ki = 160 nM) caused a systemic pressor response in spontaneously hypertensive rats that was enhanced by dietary NaCl supplementation. With these data, it is suggested that inhibition of Na+/H+ exchange in vivo has a pressor effect greater in spontaneously hypertensive rats than in WKY rats and is further enhanced by NaCl supplementation.

Reduced sodium-proton exchange activity in lymphocytes from transgenic rats

We investigated sodium-proton (Na(+)-H+) exchange activity in transgenic TGR(mRen-2)27 rats, a strain showing fulminant hypertension after the mouse Ren-2d renin gene has been integrated into its genome, in age-matched normotensive Sprague-Dawley (SD) rats, in spontaneously hypertensive rats (SHR) from the Münster strain, and in normotensive Wistar-Kyoto (WKY) rats. From each strain Na(+)-H+ exchange activity was determined in lymphocytes using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) by measuring the recovery rate of cytosolic pH (pHi) after intracellular acidification. Resting pHi was not significantly different in transgenic rats (n = 10) compared with SD rats (n = 10) (7.305 +/- 0.038 versus 7.337 +/- 0.031; mean +/- SEM), but resting pHi was significantly lower in lymphocytes from SHR (n = 12) compared with their normotensive WKY counterparts (n = 12) (7.232 +/- 0.030 versus 7.377 +/- 0.022; P < .01). Na(+)-H+ exchange activity was significantly lower in lymphocytes from transgenic rats compared with SD rats (5.102 +/- 0.561 versus 7.385 +/- 0.491 x 10(-3) dpHi/s; P < .01), whereas Na(+)-H+ exchange was significantly enhanced in lymphocytes from SHR compared with WKY rats (5.564 +/- 0.432 versus 3.921 +/- 0.433 x 10(-3) dpHi/s; P < .05). The apparent half-maximal activation of Na(+)-H+ exchange was not significantly different in the strains tested. The present study indicates that hypertension in transgenic rats is not related to Na(+)-H+ exchange overactivity.

The lymphocyte Na+/H+ antiport: activation in primary hypertension and during chronic NaCl-loading

Increased activity of the Na+/H+ antiport may be a major abnormality in essential hypertension. The activity of this transport system was investigated in lymphocytes from 13 patients with untreated essential hypertension (Ht) and 13 normotensive control subjects (Nt) on an ad libitum (130-170 mmol d-1) NaCl intake. Furthermore, the effects of different states of NaCl balance on lymphocyte Na+/H+ antiport were evaluated in two groups of Nt volunteers receiving 20 vs. 300 mmol d-1 (n = 8) and 85 vs. 200 mmol d-1 (n = 14) of NaCl for 1 week each and in seven Ht patients (20 vs. 300 mmol NaCl d-1 for 1 week each). Additionally, during the 20 and 300 mmol/d NaCl intake red blood cell membrane transport was studied in eight subjects. For the determination of lymphocyte antiport activity, cells were loaded with the cytosolic pH (pHi) indicator bis-carboxyethyl carboxyfluorescein (BCECF-AM) and acidified by addition of different amounts of Na(+)-propionate (5-40 mM). Initial pHi-recovery was taken as the activity of the antiport system and plotted against pHi-values after acidification. Non-linear regression analysis yielded higher 'apparent' maximal transport rates in Ht than Nt (Nt: 2.00 +/- 0.22; Ht: (3.81 +/- 0.59) x 10(-3) s-1; P < 0.025). In contrast, baseline pHi-values and pHi-values at half-maximal activity (pK) were identical in Nt and Ht. In normotensive control subjects on an NaCl intake of 20, 85, 200 and 300 mmol d-1 for 7 d, 'apparent' maximal transport rates averaged 2.75 +/- 0.20, 2.89 +/- 0.17, 2.81 +/- 0.18 and (3.62 +/- 0.25) x 10(-3) s-1, respectively. Thus, antiport activity was significantly (P < 0.05) stimulated on the 300 mmol d-1 intake as compared to the three other NaCl intakes. The extreme intakes of NaCl (20 vs. 300 mmol d-1) in normotensive volunteers did not affect the erythrocyte Na+/K+ pump, Na+/K+ cotransport and Na+/Li+ countertransport. Our study supports the concept that a group of patients with primary hypertension exhibit an activated Na+/H+ antiport. Furthermore, our data demonstrate that a chronic high intake of NaCl is associated with an increase in lymphocyte antiport activity towards the high values observed in primary hypertension.

DIDS-sensitive pHi regulation in single rat cardiac myocytes in nominally HCO3-free conditions

The fluorescent dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to measure pHi in the spontaneously hypertensive rat (SHR) and in normal rat cardiac myocytes under nominally HCO3-free (20 mmol/L HEPES-buffered) conditions. When only the Na-H exchanger was blocked, the intrinsic buffering power (beta i) in SHR myocytes was significantly higher than when both the Na-H exchanger and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive pHi regulators (the Na-HCO3 cotransporter and the Cl-HCO3 exchanger) were blocked. Similar low values for beta i were also found for normal rat myocytes in Na(+)-free conditions. In Cl(-)-free solution under nominally HCO3-free conditions, in both normal and SHR myocytes, the pHi slowly alkalinized (by 0.16 +/- 0.02 and 0.11 +/- 0.02 pH units, respectively); this alkalinization was also DIDS sensitive. The reacidification during NH4+ perfusion was inhibited 30.2 +/- 7.4% by DIDS. In addition, in the nominal absence of HCO3-, 100 mumol/L ATP acidified the pHi in both normal and SHR myocytes (by 0.21 +/- 0.03 and 0.33 +/- 0.03 pH units, respectively); this acidification was totally inhibited by 0.1 mmol/L DIDS. It has been shown, in rat cardiac myocytes, that ATP acidifies the pHi by 0.35 pH unit via stimulation of a DIDS-sensitive Cl-HCO3 exchanger in HCO3-containing solutions. Finally, we have shown, in normal cardiac myocytes, that two potent Na-H exchanger blockers, N-5-ethylisopropyl amiloride (EIPA) and N-5-methyl-N-isobutyl amiloride (MIA), only partially inhibited the pHi recovery from internal acidosis under nominally bicarbonate-free conditions. When DIDS was added at the same time as EIPA, pHi recovery from an internal acid loading was completely inhibited. Our results clearly demonstrate that in both normal and SHR cardiac myocytes, bicarbonate-dependent pHi regulators can be significantly activated under resting or acidified pHi in HEPES-buffered medium, probably because of the cellular production of CO2. The contribution of these bicarbonate-dependent pHi regulators, ie, the Na-HCO3 cotransporter and the Cl-HCO3 exchanger, cannot therefore be ignored even under nominally HCO3-free conditions.

Glucose-induced changes in Na+/H+ antiport activity and gene expression in cultured vascular smooth muscle cells. Role of protein kinase C

Increased Na+/H+ antiport activity has been implicated in the pathogenesis of hypertension and vascular disease in diabetes mellitus. The independent effect of elevated extracellular glucose concentrations on Na+/H+ antiport activity in cultured rat vascular smooth muscle cells (VSMC) was thus examined. Amiloride-sensitive 22Na+ uptake by VSMC significantly increased twofold after 3 and 24 h of exposure to high glucose medium (20 mM) vs. control medium (5 mM). Direct glucose-induced Na+/H+ antiport activation was confirmed by measuring Na(+)-dependent intracellular pH recovery from intracellular acidosis. High glucose significantly increased protein kinase C (PKC) activity in VSMC and inhibition of PKC activation with H-7, staurosporine, or prior PKC downregulation prevented glucose-induced increases in Na+/H+ antiport activity in VSMC. Northern analysis of VSMC poly A+ RNA revealed that high glucose induced a threefold increase in Na+/H+ antiport (NHE-1) mRNA at 24 h. Inhibiting this increase in NHE-1 mRNA with actinomycin D prevented the sustained glucose-induced increase in Na+/H+ antiport activity. In conclusion, elevated glucose concentrations significantly influence vascular Na+/H+ antiport activity via glucose-induced PKC dependent mechanisms, thereby providing a biochemical basis for increased Na+/H+ antiport activity in the vascular tissues of patients with hypertension and diabetes mellitus.

Regulation of intracellular pH in the spontaneously hypertensive rat. Role of bicarbonate-dependent transporters

Previous studies that have evaluated the Na(+)-H+ antiporter in cells from hypertensive subjects were generally performed under conditions in which HCO3-CO2, the physiological buffer system, was absent from the assay media. The objective of this study was to evaluate the activity of the Na(+)-H+ antiporter and that of the Na(+)-dependent and Na(+)-independent Cl(-)-HCO3- exchangers in cells assayed in the presence of HCO3-CO2 in the media. Lymphocytes from 6- to 8-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) rats were obtained from the thymus gland and assayed immediately after isolation. The activity of the Na(+)-H+ antiporter after stimulation by cell acidification (pHi approximately 6.4) was similar in SHR and WKY rats (18.67 +/- 1.03 and 16.12 +/- 0.92 mmol H+/L per minute, respectively). Recovery from cell alkalinization was effected by an Na(+)-independent Cl(-)-HCO3- exchanger, with maximal activity at an alkaline pHi (approximately 7.7). The stimulated activity of this Na(+)-independent Cl(-)-HCO3- exchanger was also not different between SHR and WKY cells (2.65 +/- 0.25 and 2.55 +/- 0.32 mmol H+/L per minute, respectively). Acute chloride removal produced a rise in pHi that was Na(+)-dependent and sensitive to 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) but resistant to ethylisopropylamiloride (EIPA), reflecting the activity of an Na(+)-dependent Cl(-)-HCO3- exchanger. Unlike the Na(+)-H+ exchanger and the Na(+)-independent Cl(-)-HCO3- exchanger, which had their highest activities at extremes of pHi (low pHi, Na(+)-H+ exchanger, and high pHi, Na(+)-independent Cl(-)-HCO3- exchanger), the Na(+)-dependent Cl(-)-HCO3- exchanger had its maximal activity near steady-state pHi (approximately 7.1). No significant differences were found in the stimulated activity of this exchanger between cells from SHR and WKY rats (2.23 +/- 0.26 and 2.50 +/- 0.43 mmol H+/L per minute, respectively). The kinetic properties of the Na(+)-dependent and Na(+)-independent Cl(-)-HCO3- exchanger, examined as a function of external Cl-, were also virtually identical in cells from SHR and WKY rats. We conclude that in lymphocytes from SHR and WKY rats, the activity of the two Cl(-)-HCO3- exchangers, like that of the Na(+)-H+ exchanger, is dependent on the prevailing pHi. The Na(+)-dependent Cl(-)-HCO3- exchanger has its highest activity near steady-state pHi, suggesting an important role in the cell defense against intracellular acidosis under physiological conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal acid-base excretion in normotensive salt-sensitive humans

Reduced extracellular pH and bicarbonate levels recently have been reported in normotensive salt-sensitive subjects. To assess the possible role of altered renal acid-base handling in the perturbation of acid-base status in these individuals, we measured the renal acid-base excretion after an acute oral administration of either an alkali or acid load in normotensive salt-sensitive and salt-resistant men. Twenty-four young (22 to 29 years old), healthy male volunteers were placed on a low-salt diet (20 mmol NaCl per day) for 2 weeks with either 220 mmol NaCl or placebo added to the low-salt diet for 1 week each in a randomized single-blind crossover order. Salt sensitivity was defined as a significant drop in mean arterial pressure (> 3 mm Hg, mean of 60 readings taken on the seventh day of each diet, P < .05) during the low-salt diet. On the fifth and seventh days of each week, subjects were given an oral load of either sodium citrate (0.7 mmol/kg) or ammonium chloride (2.2 mmol/kg), respectively, in a randomized order, and arterial and urinary acid-base status was assessed at baseline and followed for 8 hours thereafter. According to the above definition, 13 subjects were considered salt sensitive. During the high-salt diet, mean arterial pressure was higher in the salt-sensitive than in the salt-resistant group (P < .01). Cumulative urinary bicarbonate excretion after the administration of sodium citrate was lower in the salt-sensitive than in the salt-resistant subjects during both the low-salt (46%, P < .001) and high-salt (32%, P < .01) diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between sodium-hydrogen ion and lithium-hydrogen ion exchange in human platelets

The membrane-coupled exchange of Li+ and/or Na+ for H+ was studied in human platelets measuring intracellular pH(pHi) with a fluorescent indicator. A Li(+)-containing medium restored the internal pH of preacidified platelets to their prior pHi control value. When Na+ was replaced by Li+, similar steady-state values were attained in this system, although it was transported more slowly. The Km and Vmax were both higher with Na+ than with Li+. Exchanges of Li+ or Na+ with H+ were both blocked by ethylisopropylamiloride (EIPA) achieving half-maximal inhibition at submicromolar concentrations. The efflux Li+ or Na+ and resuspended in a choline medium exhibited an influx of H+ sensitive to EIPA. Thrombin, an activator of Na+/H+ exchange, induced a rapid increase in platelet internal pH in the presence of exogenous Li+. Thus: (1) Li+ can be substituted for Na+ in both the forward and the reverse exchange reaction; (2) Li+, while having a higher affinity than Na+ for the external site of the membrane carrier, has a lower Km and (3) Li+ as well as Na+ exchange are activated by thrombin.

Renal acid excretion and intracellular pH in salt-sensitive genetic hypertension

Acid-base status and renal acid excretion were studied in the Dahl/Rapp salt-sensitive (S) rat and its genetically salt-resistant counterpart (R). S rats developed hypertension while on a very high salt diet (8%) and while on a more physiological salt diet (1%) and remained normotensive while on a very low salt diet (0.08%). Under the high salt diet, intracellular pH measured in freshly isolated thymic lymphocytes using 2',7'-bis (carboxyethyl)-5 (6)-carboxyfluorescein acetomethyl ester, a pH-sensitive dye, was lower in S than in R rats both when measured in the presence of HCO3/CO2 (7.32 +/- 0.02 vs. 7.38 +/- 0.02, respectively, P < 0.05) and in its absence (7.18 +/- 0.04 vs. 7.27 +/- 0.02, respectively, P < 0.05). Under the high salt diet, net acid excretion was higher in S than R rats (1,777 +/- 111 vs. 1,017 +/- 73 muEq/24 h per 100 g body wt, respectively, P < 0.001), and this difference was due to higher rates of both titratable acid and ammonium excretion. Directionally similar differences in intracellular pH and net acid excretion between S and R rats were also observed in salt-restricted animals. In S and R rats placed on a normal salt intake (1%) and strictly pair-fed to control food intake as a determinant of dietary acid, net acid excretion was also higher in S than in R rats (562 +/- 27 vs. 329 +/- 21 muEq/24 h per 100 g, respectively, P < 0.01). No significant difference in either blood pH or bicarbonate levels were found between S and R rats on either the 0.08%, 1%, or 8% salt diets. We conclude that renal acid excretion is augmented in the salt-sensitive Dahl/Rapp rat. Enhanced renal acid excretion may be a marker of increased acid production by cells from subjects with salt-sensitive hypertension.

Red cell sodium-proton exchange is increased in Dahl salt-sensitive hypertensive rats

To investigate the relationship between red blood cell Na+/H+ exchange (EXC) and genetic factors in hypertension, we studied the maximal rate of the antiporter (mmol/liter cell x hr; flux units = FU) in three strains of genetically hypertensive rats. Salt-resistant Dahl rats (DR) were normotensive under low (0.02%) and high (8%) NaCl diets, while salt-sensitive Dahl rats (DS) became markedly hypertensive after four weeks on the high-NaCl diet. Na+/H+ exchange did not differ between DR and DS rats when both were fed with the low-NaCl diet (mean +/- SE, 31 +/- 3, N = 15, vs. 29 +/- 3 FU, N = 14). On the high-NaCl diet, the DR strain did not exhibit significant changes in blood pressure and antiporter activity, but the DS rats significantly increased their blood pressure and Na+/H+ exchange (57 +/- 4 FU, N = 13) versus DR rats (38 +/- 3 FU, N = 15, P < 0.02). DS rats also significantly increased blood pressure and antiporter activity when fed with high-NaCl diet for one week. These data indicate that high NaCl intake per se does not increase Na+/H+ EXC because the control DR strain did not exhibit transport and blood pressure alterations as observed in the DS strain. Milan hypertensive and spontaneously hypertensive rats (Charles River substrain) had higher blood pressures than Milan and Wistar-Kyoto normotensive rats when they were maintained for four weeks on a 1.5% NaCl diet; however, no differences were seen among normotensive and hypertensive strains in Na+/H+ exchange activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-hydrogen exchange in erythrocytes of patients with acute deep venous thromboses

The rate of delta microH(+)-induced Na/H-exchange in erythrocytes of patients with occlusive and with floating types of acute deep venous thromboses, and in control volunteers, was estimated. In patients with occlusive thrombi Na/H-exchange was revealed to be fourfold higher in comparison with patients with floating thrombi and with controls, while no difference was observed between the two latter groups.

Increased Na+/H+ exchange activity in vascular smooth muscle cells of spontaneously hypertensive rats and possible involvement of protein kinase C

1. Na+ influx into cultured vascular smooth muscle cells (VSMC) obtained from spontaneously hypertensive rats (SHR) and from Wistar-Kyoto rats (WKY) was measured. Na+ influx via the Na+/H+ exchange system was measured as the rate of 22Na+ influx into cultured VSMC sensitive to ethylisopropylamiloride (EIPA), a specific inhibitor of the exchange system. 2. The total 22Na+ influx rate in SHR was significantly higher than in WKY (6.08 +/- 0.16 vs 4.13 +/- 0.09 nmol/min per mg protein; P less than 0.001; n = 14). The EIPA (1 X 10(-4) mol/L)-sensitive 22Na+ influx rate in SHR was significantly higher than that in WKY (4.32 +/- 0.27 vs 2.17 +/- 0.14 nmol/min per mg protein; P less than 0.001; n = 14). There was no difference in EIPA-insensitive 22Na+ influx between SHR and WKY. The EIPA-sensitive 22Na+ influx rate into VSMC was significantly decreased in SHR but not in WKY by the addition of 1 X 10(-4) mol/L 1-(5-isoquinoline-sulfonyl)-methylpiperazine (H-7), an inhibitor of protein kinase C (PK-C). 3. These results suggest that the increase in Na+ influx in SHR may be due to elevation of the Na+/H+ exchange activity, and possible involvement of PK-C in the increased Na+/H+ exchange activity in VSMC from SHR.

Intracellular pH and sodium-proton exchange activity of lymphocytes in stroke-prone spontaneously hypertensive rats

1. At the age of 20 weeks, intracellular pH (pHi) of circulating lymphocytes suspended in HCO(3-)-free NaCl media was not significantly different between stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). 2. The initial recovery rate of pHi in lymphocytes tended to be greater in SHRSP than in WKY after the addition of 60 mmol/L or 120 mmol/L of NaCl, but there was no statistically significant difference. 3. The H+ equivalent efflux rate, which was a true reflection of Na(+)-H(+) activity, was significantly greater in SHRSP than in WKY (P less than 0.05). The difference in H+ equivalent efflux rate was not due to the difference in cellular buffering power between the two groups (P greater than 0.05). An increased Na(+)-H(+) exchange activity may play a partial role in the pathogenesis of hypertension.

Increased Na(+)-H+ exchange in jejunal brush border membrane vesicles of spontaneously hypertensive rats

The spontaneously hypertensive rats and their genetically matched controls, Wistar-Kyoto, serve as models of essential hypertension. The present study was undertaken to determine whether brush border membrane vesicles obtained from jejunal enterocytes of spontaneously hypertensive rats show increased Na(+)-H+ exchange as part of a generalized membrane disorder. Brush border membrane vesicles were prepared from the jejunum of adult spontaneously hypertensive rats and Wistar-Kyoto rats using an Mg2+/ethylene glycol tetraacetic acid precipitation method. Uptake of 22Na by these vesicles was found to be into an osmotically sensitive intravesicular space rather than mere binding. Initial Na+ uptake by brush border membrane vesicles was greater in spontaneously hypertensive rats than in Wistar-Kyoto rats (P less than 0.05). Higher total and amiloride-sensitive Na+ uptake in spontaneously hypertensive rats occurred in the presence of an outwardly directed pH gradient, and uptake became statistically similar to that of Wistar-Kyoto rats in the absence of a pH gradient. Moreover, amiloride-insensitive Na+ uptake under an outwardly directed pH gradient did not differ significantly between the two groups. The enhanced Na(+)-H+ activity in spontaneously hypertensive rats is not due to altered membrane permeability to protons, as is shown by acridine orange-quenching studies. Kinetic studies for amiloride-sensitive Na+ uptake showed a greater Vmax in spontaneously hypertensive rats compared with Wistar-Kyoto rats (1.46 +/- 0.05 vs. 1.08 +/- 0.08 nmol.mg protein-1.7 s-1) but the Km values were similar in the two groups. These finding, along with similar findings previously reported in vascular smooth muscle and renal tissue of SHR, strongly suggest that an increased Na(+)-H+ exchange is related to the development of hypertension.

Variations in the apparent pH set point for activation of platelet Na-H antiport

To explore the role of the Na-H antiport in essential hypertension, we studied the kinetics of cytosolic pH and external sodium activation of this transport system in platelets from 65 normotensive and essential hypertensive subjects on and off antihypertensive medications. Subjects included both blacks and whites, as well as men and women. The fluorescent dye 2'7-bis(carboxyethyl)-5,6-carboxyfluorescein was used to monitor the cytosolic pH in these cells. Platelets from black (hypertensive and normotensive) men and hypertensive white men demonstrated a highly significant alkaline shift in the apparent cytosolic pH set point for activation of the Na-H antiport. For the hypertensive subgroups, the cytosolic pH set point values (mean +/- SEM) were: white men, 7.45 +/- 0.052; white women, 7.04 +/- 0.089; black men, 7.66 +/- 0.148; and black women, 7.20 +/- 0.082. For the normotensive subgroups, the cytosolic pH set point values were: white men, 7.13 +/- 0.034; white women, 7.05 +/- 0.036; black men, 7.50 +/- 0.110; and black women, 7.20 +/- 0.176 (p = 0.0016 for race and p = 0.0001 for gender, using a three-way analysis of variance by race, gender, and hypertension). There were no race-, gender-, or blood pressure-related differences among the various cohorts in the kinetics of sodium activation of the Na-H antiport, the cellular buffering power, and basal pH. These results suggest that at basal pH the Na-H antiport is quiescent in platelets from both black and white women and normotensive white men.(ABSTRACT TRUNCATED AT 250 WORDS)

Leucocyte Na+/H+ antiport activity in type 1 (insulin-dependent) diabetic patients with nephropathy

The development of proteinuria in Type 1 (insulin-dependent) diabetic patients may depend on predisposition to essential hypertension in addition to poor glycaemic control. Previous work has shown increased leucocyte Na+/H+ antiport activity in essential hypertension and increased erythrocyte Li+/Na+ exchange in Type 1 diabetic patients with proteinuria. To test whether susceptibility to nephropathy in Type 1 diabetes was linked to abnormalities of leucocyte Na+/H+ antiport activity, we measured the intracellular pH and kinetics of the Na+/H+ antiport in 19 Type 1 diabetic subjects with, and 15 diabetic subjects without albuminuria and compared them to 25 matched normal control subjects. Intracellular pH (mean +/- SD 7.59 +/- 0.14) and maximal transport capacity of the antiport (Vmax 87.7 +/- 24.9 mmol.1-1.min-1) were higher in diabetic subjects with albuminuria compared to normotensive control subjects (pH 7.44 +/- 0.09; Vmax 55.6 +/- 10.3 mmol.l-1.min-1; p less than 0.001 for both), similar to the defect described in essential hypertension. These differences were not seen in diabetic subjects with normal urinary albumin/creatinine ratios (pH 7.46 +/- 0.09; Vmax 61.0 +/- 13.6 mmol.l-1.min-1). Buffering characteristics of the leucocytes at different pH in the Type 1 diabetic subjects with albuminuria differed from normal control subjects and diabetic subjects with normal urinary albumin/creatinine ratios. We conclude that increased leucocyte Na+/H+ antiport activity, a known marker of essential hypertension, is usually associated with nephropathy in Type 1 diabetes.

Kinetic properties of the Na+/H+ antiporter of lymphocytes from the spontaneously hypertensive rat: role of intracellular pH

Enhanced activity of the Na+/H+ antiporter is increasingly reported as a feature of cells from hypertensive subjects but the intracellular pH (ipH) dependency of its activity has not been examined. This study was designed to characterize the kinetic properties of the Na+/H+ antiporter in lymphocytes from adult spontaneously hypertensive rats (SHR) and in those from age-matched normotensive Wistar-Kyoto (WKY) controls. Steady-state ipH, estimated from the measurement of BCECF fluorescence, was significantly lower in lymphocytes from the SHR than in those from WKY rats (7.09 +/- 0.02, n = 17 and 7.17 +/- 0.03, n = 19, respectively, P less than 0.025). The velocity of the antiporter determined from the product of the change in intracellular hydrogen ion concentration (i[H+]) by the buffering power measured concurrently at each starting ipH exhibited similar kinetic parameters in SHR and WKY cells: Vmax, 72 +/- 18 vs. 79 +/- 24 mM H+/30 s; pKH, 10.04 +/- 0.87 vs. 8.49 +/- 0.80; and Hill coefficient, 1.67 +/- 0.12 vs. 1.44 +/- 0.10, respectively. Likewise, no significant differences were observed between SHR and WKY cells in either the Km (29 +/- 5 and 32 +/- 8 mM, respectively) or the Vmax (6.0 +/- 1.0 and 5.53 +/- 1.0 mM H+/30 s, respectively) of the sodium activation curve. We conclude that while the ipH of SHR lymphocytes is reduced, the kinetic properties of the Na+/H+ antiporter are virtually identical in SHR and WKY lymphocytes. Consequently, a primary abnormality in the activity of this antiporter is not an inherent feature of lymphocytes from the SHR model of genetic hypertension. We propose that the activity of the Na+/H+ antiporter in SHR cells is apt to be increased as a result of reduction in ipH which dictates a higher set point in its steady-state activity.

Effect of protein kinase C modulators on the leucocyte Na+/H+ antiport in type 1 (insulin-dependent) diabetic subjects with albuminuria

It is uncertain why only one third of Type 1 (insulin-dependent) diabetic patients develop nephropathy. One suggestion is the inheritance of a predisposition to essential hypertension. We have previously found elevated Na+/H+ antiport activity and a raised intracellular pH in leucocytes from hypertensive and Type 1 diabetic subjects with albuminuria using a novel double ionophore fluorimetric technique. These changes are not found in Type 1 diabetic subjects without albuminuria. We wished to test the effect of a protein kinase C inhibitor staurosporine (100 nmol/l) on the elevated antiport activity, and the degree of stimulation achieved by exogenous diacyl glycerol. Raised leucocyte Na+/H+ antiport activity of Type 1 diabetic subjects with albuminuria (73.8 +/- 17.2 mmol.l-1.min-1) was restored to normal levels with staurosporine (54.9 +/- 17.9 mmol.l-1.min-1, p less than 0.001). The leucocyte Na+/H+ antiport activity of diabetic subjects without albuminuria fell significantly also with staurosporine but to a lesser extent (57.3 +/- 11.6 to 50.0 +/- 12.8 mmol/l, p less than 0.003). In contrast, leucocytes from normal control subjects showed no change in antiport activity with staurosporine (54.3 +/- 8.5 to 52.6 +/- 10.4 mmol.l-1.min-1). Dioctanoyl glycerol stimulated the leucocyte Na+/H+ antiport in normal subjects and diabetic patients without albuminuria, with significantly less stimulation in diabetic patients with albuminuria. We conclude that reversal by staurosporine of the elevated Na+/H+ antiport activity in Type 1 diabetic subjects with albuminuria could indicate a role for protein kinase C in activating the antiport. This hypothesis is supported by the reduced stimulation of the antiport by dioctanoyl glycerol in this group of patients.

Reduced intracellular pH in lymphocytes from the spontaneously hypertensive rat

This study was designed to determine the cytoplasmic pH (pHi) profile of lymphocytes from a rat model of genetic hypertension that is well suited for study before and after the development of spontaneous hypertension. For this purpose, pHi was measured in thymic lymphocytes obtained from spontaneously hypertensive rats (SHR) and from age-matched Wistar-Kyoto (WKY) control rats using 2',7'-bis carboxyethyl-5,6-carboxyfluorescein (BCECF), a pH-sensitive fluorescence probe. At the age of 16-20 weeks, pHi of lymphocytes suspended in a HCO3-free HEPES-buffered solution, was markedly lower in the SHR than in the WKY rats (7.07 +/- 0.02, n = 16 and 7.22 +/- 0.01, n = 15, respectively, p less than 0.001), whereas systolic blood pressure was higher in SHR than in WKY rats (175 +/- 5.0 and 105 +/- 3.0 mm Hg, respectively, p less than 0.001). In rats less than 5 weeks of age, pHi was also lower in SHR than in WKY rat lymphocytes (7.12 +/- 0.04, n = 11 and 7.23 +/- 0.04, n = 11, respectively, p less than 0.05), although at this age systolic blood pressure was not different between the two groups (87 +/- 4.0 and 85 +/- 3.0 mm Hg, respectively). In lymphocytes suspended in a more physiological HCO3/CO2-buffered solution, pHi was again lower in the adult SHR than in the WKY rat (7.18 +/- 0.02, n = 16 and 7.31 +/- 0.02, n = 16, respectively, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased Na+/H+ antiport activity in the renal brush border membrane of SHR

Defect in renal salt excretion may play an important role in the pathogenesis of hypertension. We examined sodium (Na+) uptake by brush border membrane (BBM) vesicles of young (6 week old) spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) of the same age. SHR had lower urinary Na+ excretion (223.1 +/- 9.3 vs. 266.3 +/- 3.7 microEq/day/100 g, N = 8, P less than 0.01) and higher systolic blood pressure (98.9 +/- 1.2 vs. 82.9 +/- 1.8 mm Hg, N = 8, P less than 0.01) than WKY. BBM vesicle Na+ uptake, measured by rapid filtration technique, was higher in SHR when compared to WKY (1.44 +/- 0.03 vs. 1.01 +/- 0.06 nmol/mg/5 sec, N = 4, P less than 0.01). This increase in Na+ influx was apparent only in the present of an outward-directed proton (H+) gradient and was abolished by 1 mM amiloride. BBM permeability to H+ as assessed by acridine orange quenching was not different between SHR and WKY. Kinetic analyses of the amiloride-sensitive BBM Na+ uptake revealed a higher Vmax (2.13 +/- 0.27 vs. 0.70 +/- 0.30 nmol/mg/5 sec, N = 4, P less than 0.01) and a higher km for Na+ (3.55 +/- 0.32 vs. 1.23 +/- 0.14 mM, N = 4, P less than 0.05) in SHR. These findings thus demonstrate an intrinsic derangement in BBM Na+ transport in young SHR which is characterized by increased Na+/H+ antiport activity. This alteration in antiport activity is not attributable to changes in membrane permeability to H+, and is characterized by higher Vmax and km.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium exchange and sodium-proton exchange are mediated by the same transport system in sarcolemmal vesicles from bovine superior mesenteric artery

Several laboratories have reported that Na+-Li+ countertransport activities are increased in red blood cells from patients with essential hypertension. It has been proposed that the activity of this red blood cell transport system might reflect the activity of a similar system in vascular smooth muscle. We previously demonstrated Na+-Li+ exchange in sarcolemmal vesicles from canine artery and proposed that this transport function might be mediated by the Na+-H+ exchanger. In the present studies, however, we were unable to demonstrate Na+-Li+ countertransport in canine red blood cells. Since bovine red blood cells have a vigorous Na+-Li+ exchanger and we previously demonstrated Na+-H+ exchange in sarcolemmal vesicles from bovine artery, we wished to determine whether bovine sarcolemmal vesicles mediate Na+-Li+ exchange and whether this transport function is mediated via the Na+-H+ exchanger. We found that an outwardly directed proton or Li+ gradient stimulated 22Na+ uptake in sarcolemmal vesicles from bovine superior mesenteric artery. Li+ gradient-stimulated Na+ uptake was not due to electrical coupling between the two ions, was not affected by a change in membrane potential, and could not be explained by the parallel operation of Li+-H+ and Na+-H+ exchange. External Li+ inhibited proton gradient-stimulated Na+ uptake, and external protons inhibited Li+ gradient-stimulated Na+ uptake. Na+ efflux from vesicles was stimulated by inwardly directed gradients for Li+ or protons, and these effects were not additive. Proton efflux from vesicles was stimulated by inwardly directed gradients for Na+ or Li+, and these effects were not additive. Finally, Na+-H+ exchange and Na+-Li+ exchange in sarcolemmal vesicles were inhibited by 5-(N-ethyl-N-isopropyl)amiloride in an identical dose-dependent manner. In conclusion, Na+-Li+ countertransport could not be demonstrated in canine red blood cells, but as is the case with bovine red blood cells, sarcolemmal vesicles from bovine artery mediate Na+-Li+ countertransport. This transport function and sarcolemmal Na+-H+ exchange are mediated via a single 5-(N-ethyl-N-isopropyl)amiloride-sensitive cation exchanger with affinity for Na+, Li+, and protons. The cow, as opposed to the dog, may be a good animal model to test whether the activity of red blood cell Na+-Li+ countertransport is predictive of the activity of Na+-Li+ (and Na+-H+) exchange in vascular smooth muscle.

Atrial natriuretic peptide and angiotensin II binding sites in cerebral capillaries of spontaneously hypertensive rats

1. We carried out investigations on specific atrial natriuretic peptide (ANP) and angiotensin II (ANG) binding sites in capillaries isolated from the cerebral cortex of spontaneously hypertensive rats (SHR), an animal model of human essential hypertension, and also from Wistar Kyoto rats (WKY). 2. In an equilibrium binding study done in the presence of increasing concentrations of the radiolabeled ligands, the binding of 125I-rat alpha-ANP (1-28) [ANF-(99-126)] (125I-rANP) and 125I-ANG (5-L-isoleucine) (125I-ANG) to the cerebral capillaries was single and of a high affinity. 3. The maximum binding capacity (Bmax) and dissociation constant (Kd) in the 125I-rANP binding of 20-week-old, hypertensive SHR was significantly lower than in age-matched, normotensive WKY. Conversely, a significant increase in the Bmax of 125I-ANG binding of adult SHR was observed, with a significant decrease in the Kd. 4. There was no differences in the Bmax of 125I-rANP and 125I-ANG binding between 4-week-old, prehypertensive SHR and age-matched WKY. However, there was a significant decrease in the Kd of 125I-rANP binding of SHR. 5. As a dramatic change in the binding kinetics of 125I-rANP and 125I-ANG was noted in the cerebral capillaries of adult sustained-hypertensive SHR, the possibility that ANP and ANG play a role in the etiology of dysfunction of the blood-brain barrier complicated with hypertension, by interacting with specific receptors, would have to be considered.

Spontaneously hypertensive rat vascular smooth muscle cells in culture exhibit increased growth and Na+/H+ exchange

The cellular mechanisms responsible for abnormalities in spontaneously hypertensive rat (SHR) vascular smooth muscle cell (VSMC) growth and vasoreactivity are not defined. Because Na+/H+ exchange, which we have previously demonstrated in cultured VSMC, plays an essential role in mediating growth factor responses, we hypothesized that abnormalities in SHR growth regulation might be reflected in the activity of this transporter. To test this hypothesis, we studied DNA synthesis and Na+/H+ exchange (measured as the rate of amiloride-sensitive intracellular alkalinization or Na+ influx) in early subcultures (less than 6) of aortic VSMC from 12-wk-old SHR and Wistar Kyoto (WKY) animals. Serum-deprived SHR VSMC grew more rapidly in response to 10% serum with an increase in [3H]thymidine incorporation of 439% compared with 191% in WKY controls. Basal intracellular pH (pHi) values determined by fluorescent pH measurements were 7.37 +/- 0.04 and 7.27 +/- 0.03 (P less than 0.05) in early passage SHR and WKY, respectively. Acid recovery (initial pHi = 6.8) by SHR VSMC was faster than by WKY VSMC as measured by alkalinization (1.8 +/- 0.6 vs. 0.8 +/- 0.2 mmol H+/liter.min, P less than 0.05) or by amiloride-sensitive 22Na+ influx (14.5 +/- 1.2 vs. 4.0 +/- 0.5 nmol Na+/mg protein.min, P less than 0.05). In comparison to WKY cells early passage SHR VSMC exhibited 2.5-fold greater alkalinization and amiloride-sensitive 22Na+ influx in response to 100 nM angiotensin II. During serial passage, WKY cells acquired enhanced Na+/H+ exchange and growth rates so that by passage 6, these differences were no longer present. These findings in early cultures of SHR VSMC, removed from the in vivo neurohumoral milieu, suggest that increased Na+/H+ exchange in SHR may reflect alterations in Na+ homeostasis that might contribute to altered SHR VSMC function such as enhanced growth and vasoreactivity.

[Mechanism and significance of arteriolar media hypertrophy/ hyperplasia in arterial hypertension. Role of the Na+/H+ antiport]

The most common haemodynamic abnormality in human essential hypertension is an increase in systemic vascular resistance. Morphologic substrate for increased flow resistance is a narrowing of the lumen of arteriolar resistance vessels. During the course of essential hypertension, this is associated with an increase in wall (mainly media) thickness due to hypertrophy and hyperplasia of vascular smooth muscle cells. In contrast to concepts interpreting media thickening strictly as structural adaptation to increased perfusion pressure, various lines of evidence also point to pressure independent factors. In this context, extracellular factors such as "growth factors" as well as alterations in the activity of intracellular messenger systems must be considered. Recent studies suggest that substances generally known to act as vasoconstrictors such as angiotensin II, noradrenaline and arginine-vasopressin may also stimulate vascular smooth muscle cell growth and proliferation. Intracellular messenger systems with possible significance in the response to trophins and/or mitogens of vascular smooth muscle cells are phospholipase C, protein kinase C and the Na+/H+-antiport. These systems have been demonstrated to be altered in hypertension supporting the concept that one endogenous factor in human essential hypertension with pathophysiological significance, at least in a subgroup of patients, may be an enhanced reactivity of vascular smooth muscle cells to trophic and mitogenic stimuli. In this context, intracellular messenger systems such as phospholipase C, protein kinase C and/or the Na+/H+-antiport may play an important pathophysiological role.

Effect of protein kinase C activation on cytoskeleton and cation transport in human erythrocytes. Reproduction of some membrane abnormalities revealed in essential hypertension

Certain manifestations of alterations of membrane cytoskeleton, protein kinase C activity, and ion transport were revealed in erythrocytes of patients with essential hypertension: 1) the average volume of erythrocytes is reduced by 4%; 2) about 7% of the total number of erythrocytes is represented by cup-shaped forms compared with 1.5 to 3.0% in the control group; 3) basal phosphorylation of Band 4.9 protein is increased 1.6-fold to 1.8-fold; 4) activity of protein kinase C is increased by 60 to 70%; 5) the rate of proton electrochemical gradient (delta mu H+)-induced Na+-H+ exchange is increased twofold. Treatment of erythrocytes of healthy donors with protein kinase C activator (12-O-tetradecanoylphorbol-13-acetate) leads to similar but more marked changes in cell shape (17% of cup-shaped forms), volume reduction (by 7%), an increase of Band 4.9 protein phosphorylation (threefold), and an increase in the rate of Na+-H+ exchange (fourfold). Protein kinase activation does not modify Na+-Li+ exchange and slightly increases (by 20-50%) Na+-K+ pump activity, Na+-K+ cotransport, and the rate of 45Ca influx. It may be assumed that the increase of protein kinase C activity is one of the most probable molecular mechanisms conditioning abnormalities of the membrane skeleton and Na+-H+ exchange in primary hypertension.

Exaggerated depressor response to 6-iodoamiloride in NaCl-sensitive spontaneously hypertensive rats

The current study tested the hypothesis that NaCl-sensitive hypertension may result from increased membrane sodium channel activity. The effect of 6-iodoamiloride, and analog of the sodium channel blocker amiloride, on mean arterial pressure (MAP) was examined in conscious, freely moving NaCl-sensitive spontaneously hypertensive rats (SHR-S) fed high (8%) or normal (1%) NaCl diets. SHR-S and age-matched NaCl-resistant SHR (SHR-R) and normotensive Wistar-Kyoto (WKY) control rats were studied at 9 weeks of age after 2 weeks on either high (8%) NaCl or control (1%) NaCl diets. 6-iodoamiloride was infused intravenously in doses of 0.38 or 0.76 mg/100 g body weight, and MAP and heart rate (HR) were monitored from a femoral arterial cannula for 2 hours. The 8% NaCl diet caused a significant elevation in MAP in SHR-S but not in SHR-R or WKY. Administration of 6-iodoamiloride (both doses) produced a significant, sustained decrease in MAP in both SHR-S and SHR-R. Maximal depressor responses to high dose 6-iodoamiloride were significantly enhanced in SHR-S fed 8% NaCl (31.2 +/- 3.7 mm Hg) compared to SHR-S fed 1% NaCl (14.8 +/- 2.4 mm Hg) or SHR-R fed either 8% or 1% NaCl diets (15.6 +/- 4.2 and 10.2 +/- 3.0 mm Hg, respectively). In contrast, feeding an 8% NaCl diet had no significant effect on the depressor responses to 6-iodoamiloride in either SHR-R or WKY rats. In WKY, these doses of 6-iodoamiloride had no significant effect on MAP in either diet group. 6-iodoamiloride had no significant effect on heart rate in any group. These results support the hypothesis that the exacerbation of hypertension in SHR-S fed a high NaCl diet may result from increased membrane sodium channel activity.

The regulation of the intracellular pH in cells from vertebrates

Eukaryotic cells control their intracellular pH using ion-transporting systems that are situated in the plasma membrane. This paper describes the different mechanisms that are involved and how their activity is regulated.

Plasma membrane and its abnormalities in hypertension

The plasma membrane is composed of proteins embedded in a discontinuous fashion in a lipid bilayer. These proteins maintain the integrity of the membrane and play fundamental roles as ion transport channels and as receptors for agents that regulate cell function. The membrane is therefore an important regulator of vascular smooth muscle contraction. The plasma membrane in the hypertensive animal exhibits abnormal permeability for monovalent ions and defective calcium handling. This is reflected in fewer calcium-binding sites and, as a result, in deficient membrane stabilization. These defects have been identified in several cell types, including lymphocytes, red blood cells, adipocytes, and vascular smooth muscle cells. Evidence presented in the current review suggests that hypertension is associated with a generalized membrane defect. Abnormalities in ion transport in vascular smooth muscle cells are the most relevant to the pathogenesis of hypertension since they could be directly responsible for the rise in blood pressure. We hypothesize that the impaired stabilizing effect of calcium in vascular smooth muscle cells of hypertensive subjects renders the membrane more excitable and that this in turn leads to increased vascular reactivity and higher peripheral resistance. Peripheral vascular reactivity usually is increased in hypertension, suggesting increased responsiveness of the smooth muscle cells. Possible abnormalities of the several components of the contractile process of these cells have been investigated for the role they might play in this altered response. Abnormalities in the plasma membrane have been most clearly defined and are emphasized in this review.

Pharmacologic agents for the in vivo detection of vascular sodium transport defects in hypertension

Anatagonists to angiotensin, catecholamines, aldosterone, and vasopressin have long been used to help determine agonist roles in hypertension. We here call attention to a possible extension of this approach to detect, evaluate, and treat vascular sodium transport defects in hypertension. Two basic types of transport defects have been identified in the blood vessels of hypertensive animals, increased sodium permeability and decreased sodium pump activity. Intravenous injection of 6-iodo-amiloride, a sodium channel blocker and vasodilator, produces an immediate and sustained decrease in blood pressure in two genetic models of hypertension characterized by increased permeability of the vascular smooth muscle cell membrane to sodium (Okamoto spontaneously hypertensive rat, Dahl salt sensitive rat), whereas it produces only a transient fall in arterial pressure in two renal models of hypertension having normal sodium permeability in vascular smooth muscle cells (reduced renal mass-saline rat, one-kidney, one clip rat). Canrenone, a metabolic product of spironolactone which can compete with oubain for binding to Na+,K+-ATPase at the digitalis receptor site, decreases blood pressure in a low renin, volume expanded model of hypertension which has been shown to have depressed sodium pump activity in arteries and increased sodium pump inhibitor in plasma (reduced renal mass-saline rat) but has no effect on blood pressure in a genetic model of hypertension which has been shown to have increased sodium pump activity secondary to increased sodium permeability (spontaneously hypertensive rat). Thus, a sodium channel blocker and a competitor to ouabain binding can detect and determine the functional significance of sodium transport defects in the blood vessels of intact hypertensive animals. Studies in red and white blood cells suggest that similar defects may exist in the blood vessels of hypertensive humans. Thus, this approach, probing for vascular transport defects in the intact animal, may ultimately also be useful in the clinical setting.