Excitation-contraction coupling in resistance mesenteric arteries: evidence for NKCC1-mediated pathway

The role of SLC12A family of cation-chloride cotransporters and drug discovery methodologies

The solute carrier family 12 (SLC12) of cation-chloride cotransporters (CCCs) comprises potassium chloride cotransporters (KCCs, e.g. KCC1, KCC2, KCC3, and KCC4)-mediated Cl- extrusion, and sodium potassium chloride cotransporters (N[K]CCs, NKCC1, NKCC2, and NCC)-mediated Cl- loading. The CCCs play vital roles in cell volume regulation and ion homeostasis. Gain-of-function or loss-of-function of these ion transporters can cause diseases in many tissues. In recent years, there have been considerable advances in our understanding of CCCs' control mechanisms in cell volume regulations, with many techniques developed in studying the functions and activities of CCCs. Classic approaches to directly measure CCC activity involve assays that measure the transport of potassium substitutes through the CCCs. These techniques include the ammonium pulse technique, radioactive or nonradioactive rubidium ion uptake-assay, and thallium ion-uptake assay. CCCs' activity can also be indirectly observed by measuring γ-aminobutyric acid (GABA) activity with patch-clamp electrophysiology and intracellular chloride concentration with sensitive microelectrodes, radiotracer 36Cl-, and fluorescent dyes. Other techniques include directly looking at kinase regulatory sites phosphorylation, flame photometry, 22Na+ uptake assay, structural biology, molecular modeling, and high-throughput drug screening. This review summarizes the role of CCCs in genetic disorders and cell volume regulation, current methods applied in studying CCCs biology, and compounds developed that directly or indirectly target the CCCs for disease treatments.

Pharmacological evidence that GABA-induced relaxation of rat proximal duodenum longitudinal muscle depends on NKCC cotransporter activity and Ca2+ influx

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in adult central nervous system (CNS) synapses, but it excites immature CNS neurons as well as neurons in the myenteric plexus. The present work aimed to determine whether GABA-induced nonadrenergic, noncholinergic (NANC) neuronal-mediated relaxation of the rat duodenum is dependent on the activity of Na⁺ K⁺ Cl^- cotransporters (NKCC) and requires calcium influx. In the presence of guanethidine (3 µmol/L), atropine (3 µmol/L), and indomethacin (1 µmol/L), relaxations induced by GABA (100 µmol/L), KCl (5-10 mmol/L) and electrical field stimulation (1-8 Hz, 2 ms, 60 V), but not those induced by bradykinin (10-100 nmol/L) were abolished by lidocaine (300 µmol/L). However, only GABA-induced relaxations were reduced in a concentration-dependent manner by the NKCC1/2 inhibitors bumetanide (0.1-1 µmol/L) and furosemide (1-10 µmol/L). GABA-induced NANC neuronal relaxation was abolished by bicuculline (30 µmol/L) and inhibited by N-nitroarginine methyl ester (l-NAME, 300 µmol/L). The ω-conotoxin GVIA (1 µmol/L), which acts exclusively on neuronal Ca_V2 channels, but not on smooth muscle voltage-gated Ca²⁺ Ca_V1 channels, and nonselective blockers of these channels (verapamil 100 nmol/L and ruthenium red 10 µmol/L), reduced GABA-induced relaxations. These results showed that the activation of GABA_A receptors induces NANC nitrergic neuronal relaxations in the rat duodenum, which depend on NKCC activity and Ca_V2 channel activation, suggesting that this phenomenon results from neuronal depolarization promoted by Cl^- efflux through GABA_A receptors, with subsequent Ca²⁺ influx and nitric oxide release.

Increased intracellular Cl- concentration in pulmonary arterial myocytes is associated with chronic hypoxic pulmonary hypertension

Chloride channels play an important role in regulating smooth muscle contraction and proliferation, and contribute to the enhanced constriction of pulmonary arteries (PAs) in pulmonary hypertension (PH). The intracellular Cl^- concentration ([Cl^-]_i), tightly regulated by various Cl^- transporters, determines the driving force for Cl^- conductance, thereby the functional outcome of Cl^- channel activation. This study characterizes for the first time the expression profile of Cl^- transporters/exchangers in PA smooth muscle and provides the first evidence that the intracellular Cl^- homeostasis is altered in PA smooth muscle cells (PASMCs) associated with chronic hypoxic PH (CHPH). Quantitative RT-PCR revealed that the endothelium-denuded intralobar PA of rats expressed Slc12a gene family-encoded Na-K-2Cl cotransporter 1 (NKCC1), K-Cl cotransporters (KCC) 1, 3, and 4, and Slc4a gene family-encoded Na⁺-independent and Na⁺-dependent Cl^-/HCO₃^- exchangers. Exposure of rats to chronic hypoxia (10% O₂, 3 wk) caused CHPH and selectively increased the expression of Cl^--accumulating NKCC1 and reduced the Cl^--extruding KCC4. The intracellular Cl^- concentration ([Cl^-]_i) averaged at 45 mM and 47 mM in normoxic PASMCs as determined by fluorescent indicator MEQ and by gramicidin-perforated patch-clamp technique, respectively. The ([Cl^-]_i was increased by ∼10 mM in PASMCs of rats with CHPH. Future studies are warranted to further establish the hypothesis that the altered intracellular Cl^- homeostasis contributes to the pathogenesis of CHPH.

Novel Human NKCC1 Mutations Cause Defects in Goblet Cell Mucus Secretion and Chronic Inflammation

BACKGROUND & AIMS

Infections resulting from intestinal yeast and bacteria affect a large number of patients with deficits in absorptive or secretory epithelial transport mechanisms. The basolateral Na⁺-K⁺-2Cl^- cotransporter (NKCC1) has been implicated in intestinal epithelial fluid secretion. Two patients with deleterious heterozygous (NKCC1-DFX, DFX for Asp-Phe-stop codon) or homozygous (Kilquist) mutations in SLC12A2 (NKCC1) suffered from gastrointestinal deficits. Because of chronic infections, the colon and the small intestine of the NKCC1-DFX patient were resected surgically.

METHODS

To investigate how NKCC1 affects the integrity and function of the gut epithelia, we used a mouse model recapitulating the NKCC1-DFX patient mutation. Electron microscopy and immunostaining were used to analyze the integrity of the colonic mucus layers and immune cell infiltration. Fluorescence in situ hybridization was performed on the distal colon sections to measure bacteria translocation to the mucosa and submucosa. Citrobacter rodentium was used to measure mouse ability to clear enteric infection. A multiplex cytokine assay was used to analyze mouse inflammatory response to infection.

RESULTS

We show that NKCC1-DFX expression causes defective goblet cell mucus granule exocytosis, leading to secretion of intact granules into the lumen of the large intestine. In addition, NKCC1-DFX colon submucosal glands secrete mucus that remained attached to the epithelium. Importantly, expression of the mutant NKCC1 or complete loss of NKCC1 function leads to aggravated inflammatory response to C rodentium infection. Compared with wild-type, NKCC1-DFX mice showed decreased expression of claudin-2, a tight junction protein involved in paracellular Na⁺ and water transport and enteric infection clearance.

CONCLUSIONS

Our data indicate that NKCC1-DFX impairs gut barrier function by affecting mucus secretion and immune properties.

Na+ -K+ -2Cl- Cotransporter (NKCC) Physiological Function in Nonpolarized Cells and Transporting Epithelia

Two genes encode the Na+ -K+ -2Cl- cotransporters, NKCC1 and NKCC2, that mediate the tightly coupled movement of 1Na+ , 1K+ , and 2Cl- across the plasma membrane of cells. Na+ -K+ -2Cl- cotransport is driven by the chemical gradient of the three ionic species across the membrane, two of them maintained by the action of the Na+ /K+ pump. In many cells, NKCC1 accumulates Cl- above its electrochemical potential equilibrium, thereby facilitating Cl- channel-mediated membrane depolarization. In smooth muscle cells, this depolarization facilitates the opening of voltage-sensitive Ca2+ channels, leading to Ca2+ influx, and cell contraction. In immature neurons, the depolarization due to a GABA-mediated Cl- conductance produces an excitatory rather than inhibitory response. In many cell types that have lost water, NKCC is activated to help the cells recover their volume. This is specially the case if the cells have also lost Cl- . In combination with the Na+ /K+ pump, the NKCC's move ions across various specialized epithelia. NKCC1 is involved in Cl- -driven fluid secretion in many exocrine glands, such as sweat, lacrimal, salivary, stomach, pancreas, and intestine. NKCC1 is also involved in K+ -driven fluid secretion in inner ear, and possibly in Na+ -driven fluid secretion in choroid plexus. In the thick ascending limb of Henle, NKCC2 activity in combination with the Na+ /K+ pump participates in reabsorbing 30% of the glomerular-filtered Na+ . Overall, many critical physiological functions are maintained by the activity of the two Na+ -K+ -2Cl- cotransporters. In this overview article, we focus on the functional roles of the cotransporters in nonpolarized cells and in epithelia. © 2018 American Physiological Society. Compr Physiol 8:871-901, 2018.

Vasoconstriction triggered by hydrogen sulfide: Evidence for Na+,K+,2Cl-cotransport and L-type Ca2+ channel-mediated pathway

Objectives

This study examined the dose-dependent actions of hydrogen sulfide donor sodium hydrosulphide (NaHS) on isometric contractions and ion transport in rat aorta smooth muscle cells (SMC).

Methods

Isometric contraction was measured in ring aortas segments from male Wistar rats. Activity of Na⁺/K⁺-pump and Na⁺,K⁺,2Cl^-cotransport was measured in cultured endothelial and smooth muscle cells from the rat aorta as ouabain-sensitive and ouabain-resistant, bumetanide-sensitive components of the ⁸⁶Rb influx, respectively.

Results

NaHS exhibited the bimodal action on contractions triggered by modest depolarization ([K⁺]_o=30 mM). At 10^-4 M, NaHS augmented contractions of intact and endothelium-denuded strips by ~ 15% and 25%, respectively, whereas at concentration of 10^-3 M it decreased contractile responses by more than two-fold. Contractions evoked by 10^-4 M NaHS were completely abolished by bumetanide, a potent inhibitor of Na⁺,K⁺,2Cl^-cotransport, whereas the inhibition seen at 10^-3 M NaHS was suppressed in the presence of K⁺ channel blocker TEA. In cultured SMC, 5×10^-5 M NaHS increased Na⁺,K⁺,2Cl^- - cotransport without any effect on the activity of this carrier in endothelial cells. In depolarized SMC, ⁴⁵Ca influx was enhanced in the presence of 10^-4 M NaHS and suppressed under elevation of [NaHS] up to 10^-3 M. ⁴⁵Ca influx triggered by 10^-4 M NaHS was abolished by bumetanide and L-type Ca²⁺ channel blocker nicardipine.

Conclusions

Our results strongly suggest that contractions of rat aortic rings triggered by low doses of NaHS are mediated by activation of Na⁺,K⁺,2Cl^-cotransport and Ca²⁺ influx via L-type channels.

NKCC1 and NKCC2: The pathogenetic role of cation-chloride cotransporters in hypertension

This review summarizes the data on the functional significance of ubiquitous (NKCC1) and renal-specific (NKCC2) isoforms of electroneutral sodium, potassium and chloride cotransporters. These carriers contribute to the pathogenesis of hypertension via regulation of intracellular chloride concentration in vascular smooth muscle and neuronal cells and via sensing chloride concentration in the renal tubular fluid, respectively. Both NKCC1 and NKCC2 are inhibited by furosemide and other high-ceiling diuretics widely used for attenuation of extracellular fluid volume. However, the chronic usage of these compounds for the treatment of hypertension and other volume-expanded disorders may have diverse side-effects due to suppression of myogenic response in microcirculatory beds.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Discovery of Novel SPAK Inhibitors That Block WNK Kinase Signaling to Cation Chloride Transporters

Upon activation by with-no-lysine kinases, STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) phosphorylates and activates SLC12A transporters such as the Na(+)-Cl(-) cotransporter (NCC) and Na(+)-K(+)-2Cl(-) cotransporter type 1 (NKCC1) and type 2 (NKCC2); these transporters have important roles in regulating BP through NaCl reabsorption and vasoconstriction. SPAK knockout mice are viable and display hypotension with decreased activity (phosphorylation) of NCC and NKCC1 in the kidneys and aorta, respectively. Therefore, agents that inhibit SPAK activity could be a new class of antihypertensive drugs with dual actions (i.e., NaCl diuresis and vasodilation). In this study, we developed a new ELISA-based screening system to find novel SPAK inhibitors and screened >20,000 small-molecule compounds. Furthermore, we used a drug repositioning strategy to identify existing drugs that inhibit SPAK activity. As a result, we discovered one small-molecule compound (Stock 1S-14279) and an antiparasitic agent (Closantel) that inhibited SPAK-regulated phosphorylation and activation of NCC and NKCC1 in vitro and in mice. Notably, these compounds had structural similarity and inhibited SPAK in an ATP-insensitive manner. We propose that the two compounds found in this study may have great potential as novel antihypertensive drugs.

Arsenic exposure decreases rhythmic contractions of vascular tone through sodium transporters and K+ channels

Arsenic-contaminated drinking water is a public health problem in countries such as Taiwan, Bangladesh, United States, Mexico, Argentina, and Chile. The chronic ingestion of arsenic-contaminated drinking water increases the risk for ischemic heart disease, cerebrovascular disease, and prevalence of hypertension. Although toxic arsenic effects are controversial, there is evidence that a high concentration of arsenic may induce hypertension through increase in vascular tone and resistance. Vascular tone is regulated by the rhythmic contractions of the blood vessels, generated by calcium oscillations in the cytosol of vascular smooth muscle cells. To regulate the cytosolic calcium oscillations, the membrane oscillator model involves the participation of Ca²⁺ channels, calcium-activated K⁺ channels, Na⁺/Ca²⁺ exchange, plasma membrane Ca²⁺-ATPase, and the Na⁺/K⁺-ATPase. However, little is known about the role of K⁺ uptake by sodium transporters [Na⁺/K⁺-ATPase or Na⁺-K⁺-2Cl^- (NKCC1)] on the rhythmic contractions. Vascular rhythmic contractions, or vasomotion are a local mechanism to regulate vascular resistance and blood flow. Since vascular rhythmic contractions of blood vessels are involved in modulating the vascular resistance, the blood flow, and the systemic pressure, we suggest a model explaining the participation of the sodium pump and NKCC1 co-transporter in low dose arsenic exposure effects on vasomotion and vascular dysfunction.

Chemical library screening for WNK signalling inhibitors using fluorescence correlation spectroscopy

WNKs (with-no-lysine kinases) are the causative genes of a hereditary hypertensive disease, PHAII (pseudohypoaldosteronism type II), and form a signal cascade with OSR1 (oxidative stress-responsive 1)/SPAK (STE20/SPS1-related proline/alanine-rich protein kinase) and Slc12a (solute carrier family 12) transporters. We have shown that this signal cascade regulates blood pressure by controlling vascular tone as well as renal NaCl excretion. Therefore agents that inhibit this signal cascade could be a new class of antihypertensive drugs. Since the binding of WNK to OSR1/SPAK kinases was postulated to be important for signal transduction, we sought to discover inhibitors of WNK/SPAK binding by screening chemical compounds that disrupt the binding. For this purpose, we developed a high-throughput screening method using fluorescent correlation spectroscopy. As a result of screening 17000 compounds, we discovered two novel compounds that reproducibly disrupted the binding of WNK to SPAK. Both compounds mediated dose-dependent inhibition of hypotonicity-induced activation of WNK, namely the phosphorylation of SPAK and its downstream transporters NKCC1 (Na/K/Cl cotransporter 1) and NCC (NaCl cotransporter) in cultured cell lines. The two compounds could be the promising seeds of new types of antihypertensive drugs, and the method that we developed could be applied as a general screening method to identify compounds that disrupt the binding of two molecules.

Dietary Salt Intake Regulates WNK3–SPAK–NKCC1 Phosphorylation Cascade in Mouse Aorta Through Angiotensin II

Na–K–Cl cotransporter isoform 1 (NKCC1) is involved in the regulation of vascular smooth muscle cell contraction. Recently, the with-no-lysine kinase (WNK)–STE20/SPS1-related proline/alanine-rich kinase (SPAK)–NKCC1 phosphorylation cascade in vascular smooth muscle cells was found to be important in the regulation of vascular tone. In this study, we investigated whether the WNK–SPAK–NKCC1 cascade in mouse aortic tissue is regulated by dietary salt intake and the mechanisms responsible. Phosphorylation of SPAK and NKCC1 was significantly reduced in the aorta in high-salt–fed mice and was increased in the aorta in low-salt–fed mice, indicating that the WNK–SPAK–NKCC1 phosphorylation cascade in the aorta was indeed regulated by dietary salt intake. Acute and chronic angiotensin II infusion increased phosphorylation of SPAK and NKCC1 in the mouse aorta. In addition, valsartan, an antagonist of angiotensin II type 1 receptor, inhibited low-salt diet–induced phosphorylation of SPAK and NKCC1, demonstrating that angiotensin II activates the WNK–SPAK–NKCC1 phosphorylation cascade through the angiotensin II type 1 receptor. However, a low-salt diet and angiotensin II together did not increase phosphorylation of SPAK and NKCC1 in the aorta in WNK3 knockout mice, indicating that activation of the WNK–SPAK–NKCC1 phosphorylation cascade induced by a low-salt diet and angiotensin II is dependent on WNK3. Indeed, angiotensin II–induced increases in blood pressure were diminished in WNK3 knockout mice. In addition, decreased response to angiotensin II in the mesenteric arteries was observed in WNK3 knockout mice. Our data also clarified a novel mechanism for regulation of vascular tonus by angiotensin II. Inhibition of this cascade could, therefore, be a novel therapeutic target in hypertension.

NKCC1 and hypertension: role in the regulation of vascular smooth muscle contractions and myogenic tone

High-ceiling diuretics (HCD), known potent inhibitors of housekeeping Na(+),K(+),2Cl cotransporter (NKCC1) and renal-specific NKCC2, decrease [Cl(-)](i), hyperpolarize vascular smooth muscle cells (VSMC), and suppress contractions evoked by modest depolarization, phenylephrine, angiotensin II, and UTP. These actions are absent in nkcc1 (/) knock-out mice, indicating that HCD interact with NKCC1 rather than with other potential targets. These findings also suggest that VSMC-specific inhibitors of NKCC1 may be considered potential pharmacological therapeutic tools in treatment of hypertension. It should be underlined that side by side with attenuation of peripheral resistance and systemic blood pressure, HCD blocked myogenic tone (MT) in renal afferent arterioles. Keeping this in mind, attenuation of MT might be a mechanism underlying the prevalence of end-stage renal disease documented in hypertensive African-Americans with decreased NKCC1 activity and in hypertensive patients subjected to chronic HCD treatment. The role of NKCC1-mediated MT in protection of the brain, heart, and other encapsulated organs deserves further investigation.

Expression of Na+-K+ -2Cl- cotransporter 1 is epigenetically regulated during postnatal development of hypertension

BACKGROUND

The expression of Na(+)-K(+)-2Cl(-) cotransporter 1 (NKCC1) is upregulated in spontaneously hypertensive rat (SHR). We investigated whether expression of NKCC1 is epigenetically regulated during postnatal development of hypertension.

METHODS

The mesenteric arteries from 5-, 10-, and 18-week-old Wistar-Kyoto rats (WKY) and SHRs were subjected to vascular contraction. We determined expression levels of Nkcc1 mRNA and protein, methylation status, and histone modification of Nkcc1 promoter, and DNA methyltransferase (DNMT) activity.

RESULTS

The inhibition of dose-response curves by bumetanide, an inhibitor of NKCC1, as well as the expression of Nkcc1 mRNA and protein was comparable between 5-week-old SHR and age-matched WKY, but greater in 18-week-old SHR than in age-matched WKY. Nkcc1 promoter in WKY was getting methylated with age whereas that in SHR mostly remained hypomethylated after development of hypertension. DNMT3B was highly associated with the promoter of WKY, whereas the CXXC finger protein 1 (Cfp1) was highly bound to the promoter of SHR. At the age of 18 weeks, the DNMT activity in aorta of WKY was about threefold higher than that of SHR. The transcription-activating histone code acetyl H3 was higher in SHR than in WKY, whereas suppressive histone code dimethyl H3K9 was greater in WKY than in SHR.

CONCLUSION

It is concluded that expression of NKCC1 is epigenetically upregulated during postnatal development of hypertension. Our data indicate that maintenance of hypomethylation in Nkcc1 promoter of SHR resulting from low DNMT activity plays an important role in the upregulation of NKCC1 during development of spontaneous hypertension.

Long-term normalization of blood pressure in SHR and 1-kidney 1-clip rats by synthetic precursor of stable PAF analogue without systemic effects in normotensive rats

This study characterized the actions of the newly synthesized PAF precursor 1-hexadecyl-2-alkylcarbamoyl-glycerol (HAG) on blood pressure (BP) in male spontaneously hypertensive rats (SHR), SHR-stroke prone (SHRSP) and Wistar rats with 1-kidney 1-clip (1K1C) renovascular hypertension used as experimental models of human primary and secondary hypertension. Systolic blood pressure (SBP) in the tail artery and mean arterial pressure (MAP) in the abdominal aorta were measured by tail plethysmography and invasive pressure transducer, respectively. Intravenous treatment with 1mg/kg HAG in SHR resulted in a rapid decline of MAP from 151±4 to 127±4mmHg in 50min (p<0.001) that was maintained for 24h after injection (128±5mmHg, p<0.01). We also observed a profound hypotensive effect of HAG in SHRSP but not in normotensive Wistar rats. In 1K1C rats, the magnitude of the BP decline evoked by HAG was correlated with MAP measured before drug administration (R=0.74, p<0.005). In 1K1C rats with SBP>140mmHg, 5mg/kg/48h HAG, given orally for 14 days, decreased SBP by 20-30mmHg without an increase in the death rate and other adverse effects. Thus, our results show that intravenous and oral administration of HAG led to a long-lasting reduction of BP in experimental models of primary and secondary hypertension. In contrast to PAF and its derivatives, the hypotensive action of HAG was preserved for 24h after a single administration, was absent in normotensive animals, and was not accompanied by visible side-effects, at least during 2 weeks of treatment.

NKCC1 and hypertension: a novel therapeutic target involved in the regulation of vascular tone and renal function

PURPOSE OF REVIEW

The present review summarizes recent advances in our understanding of the mechanisms involving the housekeeping Na+, K+, 2Cl(-) cotransporter (NKCC1) in blood pressure (BP) regulation.

RECENT FINDINGS

High-ceiling diuretics (HCDs), known potent inhibitors of NKCC1, renal-specific NKCC2 and four isoforms of K+, Cl(-) cotransporters decrease [Cl(-)]i, hyperpolarize vascular smooth muscle cells and suppress myogenic tone and contractions evoked by modest depolarization, phenylephrine, angiotensin II and uridine triphosphate. These actions are absent in NKCC1(-/-) mice, indicating that HCDs interact with NKCC1 rather than with other potential targets. NKCC1-null mice have decreased baseline BP but exhibit augmented BP increment evoked by high-salt diets. NKCC1 deficiency causes approximately three-fold elevation in plasma renin concentrations and attenuates HCD-induced renin production. In addition to HCDs, NKCC1 is also inhibited by extracellular HCO3(-) in the range corresponding to its concentration in ischemic extracellular fluids.

SUMMARY

NKCC1 modulates BP through vascular and renal effects. In addition to BP regulation, the decreased baseline activity of this carrier or its suppression by chronic treatment with HCDs may lead to inhibition of myogenic tone and progression of end-stage renal disease. NKCC1 activation in ischemia-induced acidosis may contribute to stroke via glutamate release caused by astrocyte swelling.

Decreased NKCC1 activity in erythrocytes from African Americans with hypertension and dyslipidemia

BACKGROUND

Recent studies demonstrated a key role of ubiquitous isoform of Na+,K+,2Cl- co-transport (NKCC1) in regulation of myogenic tone and peripheral resistance. We examined the impact of race, gender, and plasma lipid on NKCC1 activity in French Canadians and African Americans with hypertension and dyslipidemia.

METHODS

NKCC and passive erythrocyte membrane permeability to K+, measured as ouabain-resistant, bumetanide-sensitive, and (ouabain+bumetanide)-resistant 86Rb influx, respectively, were compared in 111 French-Canadian men, 107 French-Canadian women, 26 African-American men, and 45 African-American women with essential hypertension and dyslipidemia.

RESULTS

The African-American men and women were 7 years younger and presented twofold decreased plasma triglycerides compared to their French-Canadian counterparts (P < 0.01) whereas body mass index (BMI), total cholesterol, low-density lipoprotein, and high-density lipoprotein (HDL) were not different. NKCC was respectively 50 and 38% lower in the African-American men and women than in the French Canadians (P < 0.005) without any differences in passive erythrocyte membrane permeability for K+. We did not observe any impact of age on NKCC in all groups under investigation, whereas plasma triglycerides correlated positively with the activity of this carrier in the French-Canadian men only.

CONCLUSIONS

NKCC1 activity is lower in erythrocytes of African Americans with essential hypertension and dyslipidemia than in Caucasian counterparts. We suggest that decreased NKCC1 may contribute to the feature of the pathogenesis of salt-sensitive hypertension seen in African Americans.