Pharmacologic effects and clinical evaluation of Tenapanor, a new drug for hyperphosphatemia / 中国临床药理学与治疗学

Tenapanor is a novel phosphorus-lowering drug, which mainly inhibits sodium/hydrogen exchange protein 3 (NHE3), and also reduces intestinal phosphorus absorption by down-regulating the expression of sodium phosphate co-transporter protein (NAPI). Tenapanor is mainly used for the treatment of hyperphosphatemia in patients with end-stage renal disease-hemodialysis (ESRD-HD). Diarrhea is the most common adverse reaction to this product. This article reviews Tenapanor by performing a literature search on its pharmacological effects, pharmacokinetic properties, clinical evaluation, safety, drug interactions and dosage.

Structural repurposing of SGLT2 inhibitor empagliflozin for strengthening anti-heart failure activity with lower glycosuria

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have been reapproved for heart failure (HF) therapy in patients with and without diabetes. However, the initial glucose-lowering indication of SGLT2i has impeded their uses in cardiovascular clinical practice. A challenge of SGLT2i then becomes how to separate their anti-HF activity from glucose-lowering side-effect. To address this issue, we conducted structural repurposing of EMPA, a representative SGLT2 inhibitor, to strengthen anti-HF activity and reduce the SGLT2-inhibitory activity according to structural basis of inhibition of SGLT2. Compared to EMPA, the optimal derivative JX01, which was produced by methylation of C2-OH of the glucose ring, exhibited weaker SGLT2-inhibitory activity (IC50 > 100 nmol/L), and lower glycosuria and glucose-lowering side-effect, better NHE1-inhibitory activity and cardioprotective effect in HF mice. Furthermore, JX01 showed good safety profiles in respect of single-dose/repeat-dose toxicity and hERG activity, and good pharmacokinetic properties in both mouse and rat species. Collectively, the present study provided a paradigm of drug repurposing to discover novel anti-HF drugs, and indirectly demonstrated that SGLT2-independent molecular mechanisms play an important role in cardioprotective effects of SGLT2 inhibitors.

Cardioprotective mechanism of SGLT2 inhibitor against myocardial infarction is through reduction of autosis

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular mortality in patients with diabetes mellitus but the protective mechanism remains elusive. Here we demonstrated that the SGLT2 inhibitor, Empagliflozin (EMPA), suppresses cardiomyocytes autosis (autophagic cell death) to confer cardioprotective effects. Using myocardial infarction (MI) mouse models with and without diabetes mellitus, EMPA treatment significantly reduced infarct size, and myocardial fibrosis, thereby leading to improved cardiac function and survival. In the context of ischemia and nutritional glucose deprivation where autosis is already highly stimulated, EMPA directly inhibits the activity of the Na+/H+ exchanger 1 (NHE1) in the cardiomyocytes to regulate excessive autophagy. Knockdown of NHE1 significantly rescued glucose deprivation-induced autosis. In contrast, overexpression of NHE1 aggravated the cardiomyocytes death in response to starvation, which was effectively rescued by EMPA treatment. Furthermore, in vitro and in vivo analysis of NHE1 and Beclin 1 knockout mice validated that EMPA's cardioprotective effects are at least in part through downregulation of autophagic flux. These findings provide new insights for drug development, specifically targeting NHE1 and autosis for ventricular remodeling and heart failure after MI in both diabetic and non-diabetic patients.

Up-regulation of NHE8 by somatostatin ameliorates the diarrhea symptom in infectious colitis mice model

Na⁺/H⁺ exchangers (NHEs) have been shown to be involved in regulating cell volume and maintaining fluid and electrolyte homeostasis. Pooled evidences have suggested that loss of Na⁺/H⁺ exchanger isoform 8 (NHE8) impairs intestinal mucosa. Whether NHE8 participates in the pathology of infectious colitis is still unknown. Our previous study demonstrated that somatostatin (SST) could stimulate the expression of intestinal NHE8 so as to facilitate Na⁺ absorption under normal condition. This study further explored whether NHE8 participates in the pathological processes of infectious colitis and the effects of SST on intestinal NHE8 expression in the setting of infectious colitis. Our data showed that NHE8 expression was reduced in Citrobacter rodentium (CR) infected mice. Up-regulation of NHE8 improved diarrhea symptom and mucosal damage induced by CR. In vitro, a similar observation was also seen in Enteropathogenic E. coli (EPEC) infected Caco-2 cells. Seglitide, a SST receptor (SSTR) 2 agonist, partly reversed the inhibiting action of EPEC on NHE8 expression, but SSTR5 agonist (L-817,818) had no effect on the expression of NHE8. Moreover, SST blocked the phosphorylation of p38 in EPEC-infected Caco-2 cells. Taken together, these results suggest that enhancement of intestinal NHE8 expression by SST could ameliorate the symptoms of mice with infectious colitis.

The p90rsk-mediated signaling of ethanol-induced cell proliferation in HepG2 cell line

Ribosomal S6 kinase is a family of serine/threonine protein kinases involved in the regulation of cell viability. There are two subfamilies of ribosomal s6 kinase, (p90rsk, p70rsk). Especially, p90rsk is known to be an important downstream kinase of p44/42 MAPK. We investigated the role of p90rsk on ethanol-induced cell proliferation of HepG2 cells. HepG2 cells were treated with 10~50 mM of ethanol with or without ERK and p90rsk inhibitors. Cell viability was measured by MTT assay. The expression of pERK1, NHE1 was measured by Western blots. The phosphorylation of p90rsk was measured by ELISA kits. The expression of Bcl-2 was measured by qRT-PCR. When the cells were treated with 10~30 mM of ethanol for 24 hour, it showed significant increase in cell viability versus control group. Besides, 10~30 mM of ethanol induced increased expression of pERK1, p-p90rsk, NHE1 and Bcl-2. Moreover treatment of p90rsk inhibitor attenuated the ethanol-induced increase in cell viability and NHE1 and Bcl-2 expression. In summary, these results suggest that p90rsk, a downstream kinase of ERK, plays a stimulatory role on ethanol-induced hepatocellular carcinoma progression by activating anti-apoptotic factor Bcl-2 and NHE1 known to regulate cell survival.

Oxidative Stress-Activated NHE1 Is Involved in High Glucose-Induced Apoptosis in Renal Tubular Epithelial Cells

PURPOSE: Diabetic nephropathy (DN) is a prevalent chronic microvascular complication of diabetes mellitus involving disturbances in electrolytes and the acid-base balance caused by a disorder of glucose metabolism. NHE1 is a Na+/H+ exchanger responsible for keeping intracellular pH (pHi) balance and cell growth. Our study aimed to investigate roles of NHE1 in high glucose (HG)-induced apoptosis in renal tubular epithelial cells. MATERIALS AND METHODS: Renal epithelial tubular cell line HK-2 was cultured in medium containing 5 mM or 30 mM glucose. Then, cell apoptosis, oxidative stress, NHE1 expression, and pHi were evaluated. NHE1 siRNA and inhibitor were used to evaluate its role in cell apoptosis. RESULTS: HG significantly increased cell apoptosis and the production of reactive oxygen species (ROS) and 8-OHdG (p<0.05). Meanwhile, we found that HG induced the expression of NHE1 and increased the pHi from 7.0 to 7.6 after 48 h of incubation. However, inhibiting NHE1 using its specific siRNA or antagonist DMA markedly reduced cell apoptosis stimulated by HG. In addition, suppressing cellular oxidative stress using antioxidants, such as glutathione and N-acetyl cysteine, significantly reduced the production of ROS, accompanied by a decrease in NHE1. We also found that activated cyclic GMP-Dependent Protein Kinase Type I (PKG) signaling promoted the production of ROS, which contributed to the regulation of NHE1 functions. CONCLUSION: Our study indicated that HG activates PKG signaling and elevates the production of ROS, which was responsible for the induction of NHE1 expression and dysfunction, as well as subsequent cell apoptosis, in renal tubular epithelial cells.

Modulación inflamatoria en el shock traumático: [revisión] / Inflammatory modulation in traumatic shock: [review]

Hemorrhagic hypovolemic shock secondary to trauma is an important cause of morbidity and mortality worldwide. During the last few years, new concepts have emerged and the guidelines of fluid resuscitation in these patients have been redefined. The concept of hypotensive resuscitation has been established and new colloid solutions based on starch have been manufactured, been hydroxyethyl starch in a balanced electrolytic solution, the most studied and successful one. It has been reported, as well, the positive effects of the pharmacologic modulation of the inflammatory pathways in experimental model subjects submitted to hypovolemic shock. Products such as, ethyl pyruvate and the Na+/H+ type 1 inhibitor, BIIB513, have been Studies only experimentally in rodent models using colloids as the primary resuscitation fluid. The significant improvement in the hemodinamyc, pattern and the cardiac and inflammatory indexes and mediators, has created the basis for their use in clinical trials in the near future. The systemic inflammatory response is an important cause of multiple organ failure that increases the late mortality of patients surviving the initial early phases of hypovolemic traumatic shock and its experimental modulation in rodent models with products such as ethyl pyruvate and BIIB513 has produced excellent in vivo and in vitro results.

Universalmente se considera el Shock hipovolémico de origen hemorrágico como una importante causa de morbi-mortalidad. Durante los últimos años se ha redefinido los conceptos de la reanimación con líquidos intravenosos en los pacientes con choque hipovolémico y establecido los conceptos de reanimación hipotensa con el uso de nuevos coloides derivados del almidón, tales como el hidroxietil-almidón en solución electrolítica balanceada (Hextend®). Así mismo, se ha reportado el beneficio que conlleva el uso de modificadores de la cascada inflamatoria en modelos experimentales de sujetos sometidos a choque hipovolémico hemorrágico. Productos como el etil piruvato y la BIIB513, un inhibidor selectivo del intercambiador Na+/H+ tipo 1, han sido estudiados sólo experimentalmente en modelos roedores, empleando coloides como principal elemento de reanimación. Al mejorar el perfil hemodinámico, parámetros cardíacos y niveles de mediadores inflamatorios, estos compuestos constituyen una base cierta para ser incluidos en estudios clínicos en un futuro próximo. La respuesta inflamatoria sistémica está íntimamente implicada en la patogénesis de la Falla Orgánica Múltiple, aumentando la mortalidad tardía de pacientes que sobreviven las etapas tempranas del shock hipovolémico hemorrágico traumático. Su modulación experimental con el etil piruvato o bien la BIIB513 ha dado excelente resultado tanto en modelos experimentales in vivo como in vitro.

Renal Tubular Acidosis

Renal tubular acidosis (RTA) is a metabolic acidosis due to impaired excretion of hydrogen ion, or reabsorption of bicarbonate, or both by the kidney. These renal tubular abnormalities can occur as an inherited disease or can result from other disorders or toxins that affect the renal tubules. Disorders of bicarbonate reclamation by the proximal tubule are classified as proximal RTA, whereas disorders resulting from a primary defect in distal tubular net hydrogen secretion or from a reduced buffer trapping in the tubular lumen are called distal RTA. Hyperkalemic RTA may occur as a result of aldosterone deficiency or tubular insensitivity to its effects. The clinical classification of renal tubular acidosis has been correlated with our current physiological model of how the nephron excretes acid, and this has facilitated genetic studies that have identified mutations in several genes encoding acid and base ion transporters. Growth retardation is a consistent feature of RTA in infants. Identification and correction of acidosis are important in preventing symptoms and guide approved genetic counseling and testing.

Increased Expressions of eNBC and NHE1 in Ischemic Penumbra after Permanent Middle Cerebral Artery Occlusion / 대한해부학회지

We conducted a chronological and comparative analysis of the levels of the electrogenic Na+/HCO3-cotransporter (eNBC) and Na+/H+ exchanger 1 (NHE1) on ischemic penumbra, using the rat model of permanent middle cerebral artery occlusion (pMCAO). Both eNBC and NHE1 levels were significantly higher in the ischemic penumbra from 3 h to 6 h after focal ischemia than in the sham-operated control group. The enhancement of eNBC and NHE1 production following focal ischemia may contribute to brain cell swelling or damage during ischemic penumbra through intracellular alkalinization and Na+ overload. Therefore, increases of eNBC and NHE1 in ischemic penumbra may play an important role in secondary brain cell damages following permanent focal ischemic insults.

Protective Effect of Cariporide(R) against Ischemia/Reperfusion Injury in Rat Kidney / 대한신장학회잡지

BACKGROUND:Cytoprotective effect of Na+/H+ exchanger type 1 (NHE1) inhibitors has been studied in ischemic/reperfusion (IR) injury. The aim of this study was to evaluate the renoprotective effect and the mechanism of NHE1 inhibitor (Cariporide(R)) on IR injury of rat kidney. METHODS:IR injury was produced by clamping both renal arteries and then rats were treated with intravenous (IV) Cariporide(R) (0.5 or 1.0 mg/kg) in Sprague-Dawley rats. The effects of Cariporide(R) treatment on subsequent IR injury were evaluated in terms of renal function, tubular injury, inflammatory cytokines (IL-1beta, TNF-alpha), apoptosis, and the expression of MAPKs. RESULTS:BUN and serum creatinine increased after IR injury compared with sham-operated controls. However, treatment with Cariporide(R) significantly reduced BUN and serum creatinine. IR injury caused severe destruction of renal tubular cells in the outer medulla, but treatment with Cariporide(R) decreased the tubular damage. Treatment with Cariporide(R) also significantly decreased the expression of IL-1beta and TNF-alpha mRNA compared with IR injury. Apoptotic cell death was increased with I/R injury, but was significantly decreased in kidneys treated with Cariporide(R). At molecular basis, caspase 3 protein decreased more in Cariporide(R)-treated group than in IR injury group. The expression of MAPKs significantly increased with IR injury compared with sham- operated controls. However, kidneys treated with Cariporide(R) showed further increase of ERK expression compared with IR injury, but showed a significant decrease of JNK expression. CONCLUSIONS:NHE1 inhibitors, Cariporide(R), partially prevented IR injury-induced acute renal failure by the mechanism involving apoptosis, inflammation and MAPKs.

Increased Expression of Sodium Transporters in Rats Chronically Inhibited of Nitric Oxide Synthesis

The present study was done to determine whether endogenous nitric oxide (NO) plays a role in the regulation of sodium transporters in the kidney. Male Sprague-Dawley rats were treated with NG-nitro-L-arginine methyl ester (L-NAME, 100 mg/L drinking water) for 4 weeks. Control rats were supplied with tap water without drugs. Expression of Na, K-ATPase, type 3 Na/H exchanger (NHE3), Na/K/2Cl cotransporter (BSC1), and thiazide-sensitive Na/Cl cotransporter (TSC) proteins was determined in the kidney by Western blot analysis. Catalytic activity of Na,K-ATPase was also determined. The treatment with L-NAME significantly and steadily increased the systemic blood pressure. Total and fractional excretion of urinary sodium decreased significantly, while creatinine clearance remained unaltered. Neither plasma renin activity nor aldosterone concentration was significantly altered. The alpha1 subunit expression and the catalytic activity of Na, K-ATPase were increased in the kidney. The expression of NHE3, BSC1 and TSC was also increased significantly. These results suggest that endogenously-derived NO exerts a tonic inhibitory effect on the expression of sodium transporters, including Na, K-ATPase, NHE3, BSC1, and TSC, in the kidney.

Adaptive Responses to Dexamethasone Treatment in Rat Kidney Proximal Tubules / 대한해부학회지

Excess accumulation of glucocorticoid increases acid secretion and HCO3- reabsorption in the kidney. Reabsorption of HCO3-, which almost occurs at the proximal tubule, is mediated Na+ / H+ exchanger-3 (NHE-3) and H+ -ATPase on the apical membrane and the Na + /HCO3- cotransporter-1 (NBC-1)on the basolateral membrane. Impact of glucocorticoid was investigated by immunohistochemistry and electron microscopy to correlate the changes with the effect of in vivo dexamethasone treatment for the rat kidney proximal tubule. In a control group, immunoreactivity of NHE-3 was detected in the apical membrane and the brush borders of S1, S2 and 3 segments of the proximal tubule. Immunoreactivity of NBC-1 was detected in the basolateral membrane of S1 and S2 segments of the proximal tubule. Immunoreactivity of NHE-3 and NBC-1 protein was more pronounced in dexamethasone treated groups than the control group. Dexamethasone 1 mg/kg caused most intense immunoreactivity for NHE-3 and NBC-1 protein, however, 0.01 mg/kg and 0.1 mg/kg produced less intense immunoreactivity with no appreciable differences between these lower doses of dexamethasone groups. By electron microscopy, the tubular cells of S1 segment of the control group revealed numerous mitochondria, endocytic apparatuses, lysosomes and many basal cytoplasmic processes. In dexamethasone treated groups, the cells of S1 and S2 segments of the proximal tubule had more mitochodria and more basolateral invaginations and had an increased number of more elongated microvilli, compared with the control group. The cells of the S3 segment of the control group showed scant lateral interdigitations and had a few smaller mitochondria. The cells of the S3 segment of dexamethasone treated groups had many mitochodria and an increased number of microvilli in the brush border, but revealed no difference of basolateral invaginations among the different groups of dexamethasone. These results indicate that prolonged administration of excess glucocorticoid increases NHE-3 and NBC-1 protein, and the up-regulation of these proteins could result in increased HCO3 - reabsorption in the rat renal proximal tubules. It also suggests that these adaptive responses closely correlate to morphological alterations of proximal tubular epithelial cells.

Regulations of Bicarbonate Ions in Hypokalemic Rat Kidney / 대한해부학회지

A number of acid-base or electrolyte disorders are associated with decreased or increased HCO3- reabsorption in the renal tubules. There has been a general agreement that potassium depletion induces and maintains metabolic alkalosis in rats. However, many researchers have approached such issue only from functional studies to investigate Na+/H+ exchanger (NHE-3) and Na+/HCO(3-) cotransporter (NBC) activity which closely relates to potassium depletion. In addition the results obtained vary according to their researchers. Thus the present study was employed Western blot analysis and immunohistochemistry together, to examine the alterations of expression and distribution of NHE-3 and NBC-1 with reference to HCO3- reabsorption in the kidneys of rats fed potassium free diets according to the periods. Western blot analysis demonstrated that NHE-3 protein, ~83 kDa at molecular mass, was abundantly expressed in normal group. All potassium-depleted groups showed significantly increased NHE-3 protein compared to normal group. NBC-1 protein, ~110 kDa at molecular mass, was moderately expressed in normal group. All potassium-depleted groups had much higher amounts of the protein than normal group. There was a highly increased amount of NBC-1 protein especially in K-depleted 1 week group. Immunohistochemistry showed positive immunoreactivity of NHE-3 in the apical membranes and brush borders of proximal renal tubule cells. Its reactivity was most prominent in the S3.S1 and S2 had moderate immunoreactivity. Potassium-depleted groups had an identical pattern of cellular labeling of NHE-3 protein compared with that of normal group. However the signal intensity of NHE-3 protein in potassium-depleted groups was much higher than that of normal group. Immunoreactivity of NBC-1 was observed exclusively in the basolateral plasma membranes of proximal tubule cells. There was a strong reactivity in the S1 and S2, whereas S3 did not show any reactivity. Potassium-deprived rats exhibited an identical pattern of cellular labeling of NBC-1 protein compared with that of normal rats. However, the signal intensity of NBC-1 protein was markedly increased in potassium-deprived rats. These results suggest that increased NHE-3 and NBC-1 expression resulted from potassium depletion in the renal proximal tubules, enhances HCO3-reabsorption and consequently maintains metabolic alkalosis.

Expression of mRNA Transcripts of the Na+/H+ and Cl-/HCO3- Exchanger Isoforms in Human Nasal Mucosa / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Electrolyte transport by nasal epithelia has been suggested to be important for controlling the quantity and composition of the nasal fluid and may play an important role in the development of nasal polyps. One of various mechanisms involving translocation of Na+ and Cl- across cell membranes includes electroneutral processes, such as Na+/H+ exchange (NHE) and Cl-/HCO3- exchange (AE). MATERIALS AND METHODS: The present study evaluated the presence of mRNAs for various members of the human NHE and AE gene families in human inferior turbinate mucosa and nasal polyp using RT-PCR and in situ hybridization. RESULTS: The mRNA for NHE1 was detected in human turbinate mucosa and nasal polyp while the mRNAs for NHE2 and NHE3 could not be detected in all samples examined. Of the AE isoforms, AE2 mRNA was expressed in inferior turbinate mucosa but not in nasal polyp. In situ hybridization revealed that NHE1 mRNA in the turbinate mucosa and nasal polyp was localized in the epithelial layer and submucosal glands. AE2 mRNA was also expressed in the epithelial layer and in the submucosal glands of inferior turbinate mucosa. CONCLUSION: These results indicate that the expression of AE2 mRNA is altered in nasal polyp, compared with inferior turbinate mucosa, suggesting that the altered expression of these genes in nasal polyp may cause impaired electrolyte and water transport across the epithelial cells.

Expression of H(+)-ATPase in Inner Medullary Collecting Duct Cells of Aquaporin-3-Deficient Mice / 대한해부학회지

It has been reported that the decrease in urinary pH observed in AQP1 null mice with a urinary concentrating defect is due to upregulation of H(+)-ATPase in the IMCD. This is thought to be caused by the chronically low interstitial osmolality in these animals. To explore whether increase of H(+)-ATPase expression in the IMCD is associated with changes in the prolonged decrease of interstitial osmolality, we examined the expression of H(+)-ATPase and Na(+)-H(+) exchanger (NHE3) using light and electron microscopic immunocytochemistry in the kidneys of AQP3 null mice which are polyuric and manifest a urinary concentrating defect because of an inability to create a hypertonic medullary interstitium. In both AQP3 (-/-) and AQP1 (-/-) mouse kidneys, type A intercalated cells in cortical and medullary collecting ducts are slightly activated, and strong H(+)-ATPase immunostaining was present in the apical plasma membrane of IMCD cells, whereas no H(+)-ATPase labeling was observed in IMCD cells in wild type mice. No differences of the immunoreactivity for NHE3 in the proximal tubule and thick ascending limb of loop of Henle were observed between AQP3 or AQP1 (-/-) mice and AQP3 (+/+) mouse. These results suggest that the induction of H(+)-ATPase expression in IMCD cells of AQP3 null mice, as well as AQP1 null mice, may be related to their chronically low interstitial osmolality.

Altered Expression of Renal AQP1, AQP2 and NHE3 in Puromycin Aminonucleoside Induced Nephrotic Syndrome: Intervention by Alpha-MSH Treatment / 대한신장학회잡지

BACKGROUND: We examined whether puromycin aminonucleoside (PAN)-induced nephrotic syndrome (NS) is associated with altered renal handling of water and sodium along with changes of renal abundance of aquaporins (AQP1 and AQP2) and NHE3. Next we tested the effects of alpha-melanocyte stimulating hormone (alpha- MSH), a potent anti-inflammatory drug, on the PAN-induced renal functional derangement and the changes of renal AQPs and NHE3 abundance. METHODS: PAN was administered to Sprague-Dawley rats using two protocols: protocol 1 (180 mg/kg, single iv injection) and protocol 2 (100 mg/kg, single iv injection). RESULTS: In both protocols, PAN-induced NS was associated with decreased urine concentration, manifested by an increased urine output and decreased urine osmolality and TcH2O. Consistent with this, a marked downregulation of vasopressin-regulated collecting duct AQP2 expression was seen in PAN-induced NS. In protocol 2 where rats treated with moderate dose of PAN, alpha-MSH cotreatment prevented the reduction of urine osmolality and the increase of the FENa in the PAN-induced NS. This suggests that alpha-MSH may have protective effects against the renal functional deterioration induced by PAN. The renal abundance of the AQP1, AQP2 and NHE3 was reduced in PAN-induced NS in protocol 2, as seen in protocol 1. In contrast to the functional improvement, alpha-MSH cotreatment had marginal effects in the prevention of renal AQP1, AQP2 and NHE3 downregulation in PAN-induced NS. CONCLUSION: PAN-induced NS was associated with decreased urine concentration along with reduced renal AQP2, AQP1 and NHE3 abundance. Alpha-MSH may have protective effects against the renal functional deterioration (e.g., urine osmolality and FENa). However, alpha-MSH treatment alone is less likely to prevent the marked reduction of AQP2, AQP1 and NHE3 abundance in PAN-induced NS, in contrast to the previously known dramatic effects against the ischemia-reperfusion injury in kidney and small intestine.

Changes of Urinary Acidification and Collecting Duct H(+)-ATPase Abundance in Response to Chronic Diuretic Administration / 대한신장학회잡지

PURPOSE: Commonly used diuretics such as furosemide and hydrochlorothiazide may cause metabolic alkalosis by increasing proton secretion from distal nephron. We evaluated changes in urinary acidification and abundance of proton-secreting transporters in response to chronic subcutaneous infusion of diuretics. METHODS: Osmotic minipumps were implanted into Sprague-Dawley rats to deliver 12 mg/day furoemide or hydrochlorothiazide 7.5 mg/day for 7 days. All animals were offered tap water and a solution containing 0.8% NaCl and 0.1% KCl as drinking fluid. RESULTS: Compared with vehicle-infused controls, diuretic and natriuretic responses were evident from furosemide or hydrochlorothiazide infusion. However, there were no changes in body weight, serum aldosterone and creatinine clearance between diuretic- infused(n=6) and control(n=6) rats. In both furosemide-infused and hydrochlorothiazide-infused rats, urine pH was significantly lowered compared with controls. Furosemide-infused rats showed significantly larger excretion of urinary ammonium. Semiquantitative immunoblotting was carried out from rat kidneys to investigate abundance of proximal tubule or medullary thick ascending limb Na(+)/H(+) exchanger type 3(NHE3) and collecting duct H(+)- ATPase using specific polyclonal antibodies to NHE3 and H(+)-ATPase B1 subunit, respectively. The abundance of NHE3 from cortical homogenates was not changed by either furosemide or hydrochlorothiazide infusion. However, the abundance of NHE3 from outer medullary homogenates was increased by furosemide infusion. The H(+)-ATPase B1 subunit abundance was increased by furosemide or hydrochlorothiazide infusion in both cortical and outer medullary homogenates. CONCLUSION: These increases in the abundance of proton-secreting transporters may account for the enhanced distal urinary acidification in response to chronic diuretic administration.

A novel Na+-dependent transporter and NHE3 mediate H+ efflux in the luminal membrane of the pancreatic duct: regulation by cAMP

No abstract available.