The cellular localization of increased atrial natriuretic peptide mRNA and immunoreactivity in diabetic rat kidneys

Renal Corin Is Essential for Normal Blood Pressure and Sodium Homeostasis

Atrial natriuretic peptide (ANP)-mediated natriuresis is known as a cardiac endocrine function in sodium and body fluid homeostasis. Corin is a protease essential for ANP activation. Here, we studied the role of renal corin in regulating salt excretion and blood pressure. We created corin conditional knockout (cKO), in which the Corin gene was selectively disrupted in the kidney (kcKO) or heart (hcKO). We examined the blood pressure, urinary Na⁺ and Cl⁻ excretion, and cardiac hypertrophy in wild-type, corin global KO, kcKO, and hcKO mice fed normal- and high-salt diets. We found that on a normal-salt diet (0.3% NaCl), corin kcKO and hcKO mice had increased blood pressure, indicating that both renal and cardiac corin is necessary for normal blood pressure in mice. On a high-salt diet (4% NaCl), reduced urinary Na⁺ and Cl⁻ excretion, increased body weight, salt-exacerbated hypertension, and cardiac hypertrophy were observed in corin kcKO mice. In contrast, impaired urinary Na⁺ and Cl⁻ excretion and salt-exacerbated hypertension were not observed in corin hcKO mice. These results indicated that renal corin function is important in enhancing natriuresis upon high salt intakes and that this function cannot be compensated by the cardiac corin function in mice.

Anatomophysiology of the Henle's Loop: Emphasis on the Thick Ascending Limb

The loop of Henle plays a variety of important physiological roles through the concerted actions of ion transport systems in both its apical and basolateral membranes. It is involved most notably in extracellular fluid volume and blood pressure regulation as well as Ca²⁺ , Mg²⁺ , and acid-base homeostasis because of its ability to reclaim a large fraction of the ultrafiltered solute load. This nephron segment is also involved in urinary concentration by energizing several of the steps that are required to generate a gradient of increasing osmolality from cortex to medulla. Another important role of the loop of Henle is to sustain a process known as tubuloglomerular feedback through the presence of specialized renal tubular cells that lie next to the juxtaglomerular arterioles. This article aims at describing these physiological roles and at discussing a number of the molecular mechanisms involved. It will also report on novel findings and uncertainties regarding the realization of certain processes and on the pathophysiological consequences of perturbed salt handling by the thick ascending limb of the loop of Henle. Since its discovery 150 years ago, the loop of Henle has remained in the spotlight and is now generating further interest because of its role in the renal-sparing effect of SGLT2 inhibitors. © 2022 American Physiological Society. Compr Physiol 12:1-21, 2022.

Atrial Natriuretic Peptide: Structure, Function, and Physiological Effects: A Narrative Review

Atrial natriuretic peptide (ANP) is a cardiac peptide with multiple physiological effects, including natriuresis, blood pressure regulation, and renin-angiotensin-aldosterone system (RAAS) antagonism. Pre-proANP is synthesized in the atria and must be extensively cleaved by the protease corin to produce the mature 28 amino acid ANP. The downstream signaling pathway of ANP acts through the guanylyl cyclase receptor and the second messenger cGMP. Studies on ANP's physiological effects have demonstrated its activity on channels present in the apical membrane in the renal nephron, potentially inhibiting or decreasing sodium reabsorption. Recent research has also identified several clinical conditions, such as dilated cardiomyopathy, renal failure, and aging, associated with increased and decreased ANP levels. ANP levels could serve as a potential biomarker for the diagnosis of acute stages of heart failure, and ANP infusion could have a role in the management of acute or chronic heart failure.

Function and regulation of corin in physiology and disease

Atrial natriuretic peptide (ANP) is of major importance in the maintenance of electrolyte balance and normal blood pressure. Reduced plasma ANP levels are associated with the increased risk of cardiovascular disease. Corin is a type II transmembrane serine protease that converts the ANP precursor to mature ANP. Corin deficiency prevents ANP generation and alters electrolyte and body fluid homeostasis. Corin is synthesized as a zymogen that is proteolytically activated on the cell surface. Factors that disrupt corin folding, intracellular trafficking, cell surface expression, and zymogen activation are expected to impair corin function. To date, CORIN variants that reduce corin activity have been identified in hypertensive patients. In addition to the heart, corin expression has been detected in non-cardiac tissues, where corin and ANP participate in diverse physiological processes. In this review, we summarize the current knowledge in corin biosynthesis and post-translational modifications. We also discuss tissue-specific corin expression and function in physiology and disease.

Expression patterns of natriuretic peptides in pre-hibernating and hibernating Anatolian ground squirrel (Spermophilus xanthoprymnus) kidney

Hibernation is characterized by marked suppression of renal function. Natriuretic peptides (NPs) are involved in the regulation of renal function. However, the role of NPs in the renal function during hibernation remains unclear. We aimed to investigate the distribution patterns of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in Anatolian ground squirrel (Spermophilus xanthoprymnus) kidneys during pre-hibernation and hibernation periods. Cortical proximal tubules showed weak ANP immunoreactivity, with moderate staining on the brush border during the pre-hibernation period. In the hibernation period, moderate ANP immunoreactivity was seen in cortical proximal tubules, with very weak reaction in hibernating cortical distal tubules, medullary proximal and collecting tubules. Cortical proximal and distal tubules of both periods had strong and weak BNP immunoreactivity, respectively. Medullary proximal, distal and Henle's loop segments showed very weak BNP immunoreactivity during pre-hibernation. Medullary distal, proximal and collecting tubules and Henle's loop segments had moderate staining during hibernation. In both periods, cortical proximal tubules displayed strong immunoreactivity to CNP. Distal tubules had moderate CNP staining during pre-hibernation, albeit weak staining during hibernation. Medullary proximal tubules exhibited moderate to strong immunoreactivity during pre-hibernation. Medullary distal and proximal tubules had weak and moderate CNP staining, respectively, during pre-hibernation. In both periods, Henle's loop segments displayed moderate CNP immunoreactivity. Glomeruli had similar weak ANP, BNP and CNP staining in both periods. These results suggest that heterothermic conditions differently affected the expression of NPs in the squirrel kidney. This different expression of NPs may contribute to the renal adaptation during hibernation.

Upregulation of Neuronal Nitric Oxide Synthase mRNA and Protein in Adrenal Medulla of Water-deprived Rats

Experiments were performed to investigate whether adrenal neuronal nitric oxide synthase (nNOS) mRNA and protein expression are responsive to alterations in body volume. Using an RT-PCR technique, the relative quantities of nNOS mRNA as well as the tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA in the adrenals of water-deprived rats significantly increased from 12 hr to 4 days. In situ hybridization and immunohistochemical study showed that water deprivation activated nNOS mRNA and protein expression in the adrenal medulla. Four days after water deprivation, nNOS protein expression determined by Western blot significantly increased in the adrenal gland. Our results are the first to demonstrate that nNOS syntheses in the adrenal medulla are markedly increased in water-deprived rats. This study also indicates that the upregulation of nNOS synthesis of the adrenal medulla is associated with the activation of adrenal medullary function in the face of volume depletion.

Localization of corin and atrial natriuretic peptide expression in human renal segments

Atrial natriuretic peptide (ANP)-mediated natriuretic response is a well-established cardiac endocrine function. Corin is a transmembrane protease that activates ANP in the heart. Corin expression has been detected in non-cardiac tissues including the kidney. Here we examined corin, pro-ANP/ANP and natriuretic peptide receptor-A (NPR-A) expression in human renal segments. By immunostaining and in situ hybridization, we found similar corin, pro-ANP/ANP and NPR-A protein and mRNA expression in human renal segments. The expression was most abundant in the proximal convoluted tubules and the medullary connecting ducts. In the proximal tubules, corin protein was present in the apical membrane region underneath the brush border where the ANP-degrading protease neprilysin was abundant. These results suggest that corin-mediated pro-ANP activation may occur in renal segments and that locally produced ANP may act in an autocrine manner to regulate sodium and water reabsorption in situ Our results also point to the proximal convoluted tubules as a major site for local ANP action. Such a renal corin/ANP autocrine mechanism may differ from the cardiac corin/ANP endocrine mechanism in regulating sodium homoeostasis under physiological and pathological conditions.

ANP-induced signaling cascade and its implications in renal pathophysiology

The balance between vasoconstrictor/sodium-retaining and vasodilator/natriuretic systems is essential for maintaining body fluid and electrolyte homeostasis. Natriuretic peptides, such as atrial natriuretic peptide (ANP), belong to the vasodilator/natriuretic system. ANP is produced by the conversion of pro-ANP into ANP, which is achieved by a proteolytical cleavage executed by corin. In the kidney, ANP binds to the natriuretic peptide receptor-A (NPR-A) and enhances its guanylyl cyclase activity, thereby increasing intracellular cyclic guanosine monophosphate production to promote natriuretic and renoprotective responses. In the glomerulus, ANP increases glomerular permeability and filtration rate and antagonizes the deleterious effects of the renin-angiotensin-aldosterone system activation. Along the nephron, natriuretic and diuretic actions of ANP are mediated by inhibiting the basolaterally expressed Na(+)-K(+)-ATPase, reducing apical sodium, potassium, and protein organic cation transporter in the proximal tubule, and decreasing Na(+)-K(+)-2Cl(-) cotransporter activity and renal concentration efficiency in the thick ascending limb. In the medullary collecting duct, ANP reduces sodium reabsorption by inhibiting the cyclic nucleotide-gated cation channels, the epithelial sodium channel, and the heteromeric channel transient receptor potential-vanilloid 4 and -polycystin 2 and diminishes vasopressin-induced water reabsorption. Long-term ANP treatment may lead to NPR-A desensitization and ANP resistance, resulting in augmented sodium and water reabsorption. In mice, corin deficiency impairs sodium excretion and causes salt-sensitive hypertension. Characteristics of ANP resistance and corin deficiency are also encountered in patients with edema-associated diseases, highlighting the importance of ANP signaling in salt-water balance and renal pathophysiology.

Increased expression of visfatin in monocytes and macrophages in male acute myocardial infarction patients

We demonstrated that visfatin expressed in monocytes and neutrophils and increased their reactivity in male acute ST-segment elevation myocardial infarction patients. Furthermore, visfatin was strongly appeared in lipid rich coronary rupture plaques and macrophages. These results suggest another explanation about leukocytes mediated visfatin that may play a pathogenesis role in coronary vulnerable plaques rupture.

Local action of endogenous renal tubular atrial natriuretic peptide

Up-regulation of atrial natriuretic peptide (ANP) mRNA in the kidneys in several disorders has been demonstrated; however, evidence that ANP synthesized by the kidney exerts a local function has never been produced. Therefore, we investigated whether endogenous ANP could modulate high glucose-stimulated TGF-beta1, collagen type I and nuclear factor-kappaB (NF-kappaB) in NRK-52E cells using transfection of ANP and ANP small interfering RNA (siANP). NRK-52E cells were grown with or without transfection with ANP plasmid; cells were also transfected with ANP siRNA or control siRNA. These cells were then stimulated with a high glucose concentration to modulate ANP, TGF-beta1, collagen type I, NF-kappaB and IkappaB-alpha, and the results showed that ANP, TGF-beta1, collagen type I and NF-kappaB significantly increased in untransfected cells, and the transfection of ANP significantly attenuated high glucose-activated TGF-beta1, collagen I and NF-kappaB expression. ANP siRNA knocked-down ANP but significantly increased TGF-beta1 and collagen I under normal glucose conditions; ANP siRNA decreased IkappaB-alpha but strongly enhanced high glucose-activated TGF-beta1, collagen type I and NF-kappaB. In contrast, medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I expression in NRK-52E cells transfected with siANP. In conclusion, our results demonstrated that siANP increased activation of TGF-beta1, collagen type I and NF-kappaB in NRK-52E cells under high glucose conditions, and medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I. This is the first study to demonstrate the auto/paracrine action of endogenous ANP in renal tubular cells on the attenuation of hyperglycemia-activated TGF-beta1 and NF-kappaB expression. J. Cell. Physiol. 219: 776-786, 2009. (c) 2009 Wiley-Liss, Inc.

Natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system has inhibitory effects in renal fibrosis in mice

OBJECT

This study was designed to examine whether natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system attenuates renal fibrosis in a unilateral ureteral obstruction (UUO) model and also examined the mechanism involved.

METHODS

Three groups were studied: untreated UUO in wild-type mice; untreated UUO in NPR-A KO mice; and ANP treated (0.05 microg/kg/min) UUO in wild-type mice. We measured histological and immunohistochemical findings (alpha-SMA and F4/80), tissue cGMP levels, various mRNA expression levels by real-time PCR analysis, and transcription factor levels (AP-1 and NF-kappaB) in renal tissue.

RESULTS

Compared with wild-type UUO mice, NPRA-KO UUO mice had abnormal morphological findings (fibrous area: +26%, alpha-SMA expression: +30%) with lower tissue cGMP levels and increases in the mRNA expression levels of TGF-beta, collagen I, collagen III, PAI-1, renin and angiotensinogen, whereas there were no differences in F4/80 positive cells or the mRNA expression levels of ICAM-1, osteopontin, or MCP-1 between the two groups. In contrast, ANP pre-treatment significantly improved morphological changes with increase of tissue cGMP levels and reduction in the mRNA expression level of TGF-beta, collagen I, collagen III, PAI-1, ICAM-1, osteopontin, MCP-1, renin, and angiotensinogen. NPRA-KO UUO mice had higher AP-1 levels than wild-type UUO mice and ANP pre-treatment reduced AP-1 and NF-kappaB activity.

CONCLUSION

The endogenous natriuretic peptide/NPR-A system may inhibit renal fibrosis partly via inhibition of the angiotensin/AP-1/TGF-beta/collagen pathway and exogenous ANP pre-treatment may inhibit it partly via both the angiotensin/AP-1/TGF-beta/collagen and NF-kappaB/inflammatory pathways.

Atrial natriuretic peptide attenuates high glucose-activated transforming growth factor-beta, Smad and collagen synthesis in renal proximal tubular cells

Atrial natriuretic peptide, besides its role in the regulation of volume homeostasis, has been noted to exert cytoprotective effects in several cell types from hypoxia. The present study was performed to explore the effect of ANP on high glucose-activated transforming growth factor-beta1 (TGF-beta1), Smad and collagen synthesis in renal proximal epithelial cells. Cultured NRK-52E cells were divided into five groups: (1) normal glucose (5.5 mM), (2) high glucose (35 mM), (3) D-mannitol (29.5 mM), (4) high glucose plus ANP (10(-6)-10(-9) M), and (5) high glucose plus ANP (10(-6) M) and guanylate cyclase inhibitor LY83583 (10(-7) M) groups. Messenger RNA levels of TGF-beta1, Smad2, and collagens were measured by RT-PCR. ELISA, immunocytochemistry and Western blotting were used to detect protein levels of TGF-beta1, Smad2, phospho-Smad 2/3 and collagen type 1. We found high glucose to significantly increase mRNA levels of TGF-beta1, Smad 2, collagen types I and III and protein levels of TGF-beta1, phospho-Smad 2/3 and collagen type 1, but mannitol did not affect their expression. The addition of ANP significantly attenuated high glucose-enhanced mRNA and protein levels of TGF-beta1, Smad and collagens. LY83583 blocked the influence of ANP on high glucose-activated TGF-beta1, Smad and collagen synthesis. This is the first study to demonstrate that activation of TGF-beta1, Smad and collagen synthesis stimulated by high glucose can also be inhibited by exogenous ANP in renal tubular epithelial cells.

Down-regulation of adrenal neuronal nitric oxide synthase mRNAs and proteins after deoxycorticosterone acetate-salt treatment in rats

The aim of this study was to evaluate the possible changes of adrenal neuronal nitrite oxide synthase (nNOS) messenger RNA (mRNA) and protein of rats after deoxycorticosterone acetate (DOCA)-salt treatment. We determined adrenal nNOS expression in 12 vehicle-treated and 13 DOCA-salt-treated rats by in situ hybridization, immunohistochemistry, and multiplex RT-PCR methods. Adrenal nNOS was also detected by Western blot in five vehicle-treated and five DOCA-salt-treated rats. The results showed that adrenal nNOS mRNA and nNOS immunoreactivities were mainly localized in the medulla and some in the regions of zona glomerulosa. DOCA-salt treatment inactivated nNOS mRNA and peptide expression prominent in the adrenal medulla and slight in the zona glomerulosa. The relative quantities of nNOS mRNA in the adrenals of the DOCA-salt-treated group was 8.8-fold decreased. At the same time, the relative quantities of steroid acute regulatory protein mRNA and phenylethanolamine N-methyltransferase mRNA in the adrenals of the DOCA-salt-treated group were significantly decreased. Western blots showed that total adrenal nNOS were 3.7-fold down-regulated after DOCA-salt treatment. Our results indicated that the down-regulation of adrenal nNOS synthesis might be associated with the inactivation of adrenal function in face of volume expansion.

Localization of ANP-synthesizing cells in rat stomach

AIM: To study the morphological positive expression of antrial natriuretic peptide (ANP)-synthesizing cells and ultrastructural localization and the relationship between ANP-synthesizing cells and microvessel density in the stomach of rats and to analyze the distribution of the three histologically distinct regions of ANP-synthesizing cells.

METHODS: Using immunohistochemical techniques, we studied positive expression of ANP-synthesizing cells in rat stomach. A postembedding immunogold microscopy technique was used for ultrastructural localization of ANP-synthesizing cells. Microvessel density in the rat stomach was estimated using tannic acid-ferric chloride (TAFC) method staining. Distribution of ANP-synthesizing cells were studied in different regions of rat stomach histochemically.

RESULTS: Positive expression of ANP-synthesizing cells were localized in the gastric mucosa of rats. Localization of ANP-synthesizing cells identified them to be enterochrochromaffin cells (EC) by using a postembedding immunogold electron microscopy technique. EC cells were in the basal third of the cardiac mucosa region. ANP-synthesizing cells existed in different regions of rat stomach and its density was largest in the gastric cardiac region, and the distribution order of ANP-synthesizing cells in density was cardiac region, pyloric region and fundic region in mucosa layer. We have also found a close relationship between ANP-synthesizing cells and microvessel density in gastric mucosa of rats using TAFC staining.

CONCLUSION: ANP-synthesizing cells are expressed in the gastric mucosa. EC synthesize ANP. There is a close relationship between ANP-synthesizing cells and microvessel density in gastric mucosa of rats.The distribution density of ANP-synthesizing cells is largest in the gastric cardiac region.

Relationship between atrial natriuretic peptide-immunoreactive cells and microvessels in rat gastric mucosa

AIM

To investigate the ultrastructural localization of atrial natriuretic peptide (ANP)-synthesizing cells and the relationship between ANP-synthesizing cells and microvessels in rat gastric mucosa.

METHODS

Immunohistochemistry techniques and postembedding immunoelectron microscopy techniques were used to validate the findings regarding the expression of ANP-synthesizing cells and the ultrastructural localization of ANP-synthesizing cells in the gastric mucosa. Histochemistry techniques and the tannic acid-ferric chloride method (TA-Fe staining method) were used to reveal microvessel density and the distribution of ANP-synthesizing cells in different regions of the stomach.

RESULTS

Cells expressing ANP were localized and ANP-synthesizing cells were identified as enterochromaffin (EC) cells in the gastric mucosa. ANP-synthesizing cells existed in different regions of the stomach. The percentage ANP-synthesizing cells in the mucosa was greatest in the fundus (46.7%+/-5.3%), intermediate in the antrum (40.1%+/-4.5%), and least in the body (21.6%+/-3.6%). There was a positive relationship between the percentage of ANP-synthesizing cells and the density of microvessels in the antral mucosa, but not in the fundus or body mucosa.

CONCLUSION

ANP is synthesized by EC cells in rat gastric mucosa, and ANP-synthesizing cells are most dense in the gastric fundus. ANP may act not only as a regional autocrine and/or paracrine regulator, but also as an endocrine regulatory peptide in the gastrointestinal tract.

WOX1 Is Essential for UVB Irradiation–Induced Apoptosis and Down-Regulated via Translational Blockade in UVB-Induced Cutaneous Squamous Cell Carcinoma In vivo

PURPOSE

We investigated the role of candidate tumor suppressor and proapoptotic WOX1 (also named WWOX, FOR, or WWOXv1) in UVB-induced apoptosis and formation of cutaneous squamous cell carcinomas (SCC).

EXPERIMENTAL DESIGN

Expression of WOX1 and family proteins (WWOX) in human primary cutaneous SCCs was examined by immunohistochemistry, in situ hybridization, and reverse transcription-PCR. UVB irradiation-induced WOX1 activation (Tyr33 phosphorylation and nuclear translocation), apoptosis, and cutaneous SCC formation were examined both in vitro and in vivo.

RESULTS

Up-regulation of human WOX1, isoform WOX2, and Tyr33 phosphorylation occurred during normal keratinocyte differentiation before cornification and death. Interestingly, significant reduction of these proteins and Tyr33 phosphorylation was observed in nonmetastatic and metastatic cutaneous SCCs (P < 0.001), but without down-regulation of WWOX mRNA (P > 0.05 versus normal controls), indicating a translational blockade of WWOX mRNA to protein. During acute exposure of hairless mice to UVB, WOX1 was up-regulated and activated in epidermal cells in 24 hours. In parallel with the clinical findings in humans, chronic UVB-treated mice developed cutaneous SCCs in 3 months, with significant reduction of WOX1 and Tyr33 phosphorylation and, again, without down-regulation of WWOX mRNA. Human SCC-25 and HaCaT cells were transfected with small interfering RNA-targeting WOX1 and shown to resist UVB-induced WOX1 expression, activation, and apoptosis.

CONCLUSIONS

WOX1 is essential for UVB-induced apoptosis and likely to be involved in the terminal differentiation of normal keratinocytes. During UVB-induced cutaneous SCC, epidermal cells have apparently prevented the apoptotic pressure from overexpressed WOX1 by shutting down the translation machinery for WWOX mRNA.

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Decreased synthesis of glomerular adrenomedullin in patients with IgA nephropathy

Adrenomedullin (AM) immunostaining and gene expression have seldom been measured in human kidneys. Because previous studies have shown that AM exerts antiproliferative effects on rat mesangial cells in vitro and that urine AM levels are decreased in patients with chronic glomerulonephritis, we measured glomerular AM and its gene expression in patients with primary IgA nephropathy (IgAN). Glomerular AM was measured by immunohistochemical staining, and glomerular AM mRNA was measured by in situ hybridization. Plasma and urine AM were measured by radioimmunoassay. The results showed that both the intensity of immunostaining for glomerular AM and the glomerular expression of AM mRNA were significantly decreased in IgAN patients compared with normal controls (both P < .05). Similar results were not observed in patients with non-IgA MsPGN. Glomerular AM immunostaining and glomerular AM mRNA expression were significantly correlated ( P < .001), and both were negatively correlated with the number of glomerular cells ( P < .05 and < .01, respectively). Both glomerular AM immunostaining and glomerular AM mRNA expression were correlated with urine AM levels (both P < .001), but not with plasma AM levels. The urine AM level was significantly lower in IgAN patients than in normal controls ( P < .01), whereas the plasma level was not different between the 2 groups. Our findings indicate that glomerular production of AM was decreased in patients with IgA nephropathy and that this lack of glomerular AM may be related to the pathogenesis of this mesangial disease.

C-type natriuretic peptide as a podocyte hormone and modulation of its cGMP production by glucose and mechanical stress

BACKGROUND

High glucose and mechanical strain resulting from capillary hypertension are relevant risk factors affecting glomerular cells in diabetes. Altered activity of the natriuretic peptide (NP) system acting via vasorelaxing cyclic guanosine 5' monophosphate (cGMP) has been proposed to be one of the reasons for diabetes-dependent impairment of kidney function. Podocytes possess the NP receptors (NPRs) coupled to particular guanylyl cyclase. We investigated whether mechanical stress and high ambient glucose influence cGMP generation in podocytes stimulated with NPs. Additionally, the C-type natriuretic peptide (CNP) system has been characterized in these cells.

METHODS

Conditionally immortalized mouse podocytes were stimulated with NP for 15 minutes and cGMP was determined by enzymatic immunoassay. The mRNA expression for CNP and CNP-specific NPR-B was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, cGMP synthesis was measured in cells exposed to mechanical stress and to 30 mmol/L glucose for 3 days.

RESULTS

Production of cGMP upon stimulation of the NPR-B receptor with CNP and inhibition by an antagonist HS-142-1 was dose-dependent. RT-PCR showed that podocytes express mRNA not only for NPR-B but also for CNP. Mechanical stress reduced the cGMP response by 50%, both to atrial natriuretic peptide (ANP) and to CNP. Conversely, upon high glucose, the CNP-induced production of cGMP was elevated twofold in stretched and in control cells. Furthermore, as compared to ANP, stimulation with CNP caused a larger increase in cGMP levels in stretched as well as in nonstretched cells.

CONCLUSION

Expression of CNP together with potent NPR-B receptors suggests that in podocytes, CNP may act in an autocrine and/or paracrine manner. Furthermore, in a diabetic kidney, high glucose and mechanical stress may modulate the CNP-dependent cGMP production in podocytes in an opposite manner.

Role of calcium-activated potassium currents in CNP-induced relaxation of gastric antral circular smooth muscle in guinea pigs

AIM: To investigate ion channel mechanism in CNP-induced relaxation of gastric circular smooth muscle in guinea pigs.

METHODS: Spontaneous contraction of gastric smooth muscle was recorded by a four-channel physiograph. The whole cell patch-clamp technique was used to record calcium-activated potassium currents and membrane potential in the gastric myocytes isolated by collagenase.

RESULTS: C-type natriuretic peptide (CNP) markedly inhibited the spontaneous contraction in a dose-dependent manner in gastric circular smooth muscle in guinea pigs. Ly83583, an inhibitor of guanylate cyclase, weakened CNP-induced inhibition on spontaneous contraction but Zaparinast, an inhibitor of cGMP sensitive phosphoesterase, potentiated CNP-induced inhibition in gastric circular smooth muscles. The inhibitory effects of CNP on spontaneous contraction were blocked by tetrathylammonium (TEA), a nonselective potassium channel blocker. C N P hyperpolarized membrane potential from -60.0 mV ± 2.0 mV to -68.3 mV ± 3.0 mV in a single gastric myocyte. CNP increased calcium-activated potassium currents (I_K(ca)) in a dose-dependent manner in gastric circular myocytes. CNP also increased the spontaneously transient outward currents (STOCs). Ly83583 partly blocked CNP-induced increase of calcium-activated potassium currents, but Zaparinast potented the effect.

CONCLUSION: CNP inhibits spontaneous contraction, and potassium channel may be involved in the process in gastric circular smooth muscle of guinea pigs. CNP-induced increase of I_K(ca) is mediated by a cGMP dependent pathway.