Novel Role of the Calcium-Sensing Receptor in Blood Pressure Modulation

Calcium, Its Regulatory Hormones, and Their Causal Role on Blood Pressure: A Two-Sample Mendelian Randomization Study

CONTEXT

Vitamin D (Vit-D), parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23) are the major calciotropic hormones involved in the regulation of blood calcium levels from the intestine, kidney, and bone through a tight endocrine feedback loop system. Altered levels of calcium itself or through the effect of its regulatory hormones could affect blood pressure (BP), but the exact mechanisms remain unclear.

OBJECTIVE

To evaluate whether a causal relationship exists between serum calcium level and/or the regulatory hormones involved in its homeostasis with BP, we performed a two-sample Mendelian randomization (MR) study.

METHODS

From 4 large genome-wide association studies (GWAS) we obtained independent (r2 < 0.001) single nucleotide polymorphisms (SNPs) associated with serum calcium (119 SNPs), Vit-D (78 SNPs), PTH (5 SNPs), and FGF23 (5 SNPs), to investigate through MR their association with systolic BP (SBP) and diastolic BP (DBP) in a Swedish urban-based study, the Malmö Diet and Cancer study (n = 29 298). Causality was evaluated by the inverse variance weighted method (IVW) and weighted median, while MR Egger and MR-PRESSO were used as sensitivity analyses.

RESULTS

Genetically predicted serum calcium level was found to be associated with DBP (IVW: beta = 0.10, SE = 0.04, P = 0.007) and SBP (IVW: beta = 0.07, SE = 0.04, P = 0.04). Genetically predicted Vit-D and PTH showed no association with the traits, while FGF23 was inversely associated with SBP (IVW: beta = -0.11, SE = 0.04, P = 0.01), although this association lost statistical significance in sensitivity analysis.

CONCLUSION

Our study shows a direct association between genetically predicted calcium level and DBP, and a weaker association with SBP. No such clear association was found for genetically predicted calciotropic hormone levels. It is of interest to detect which target genes involved in calcium homeostasis mediate the effect of calcium on BP, particularly for improving personalized intervention strategies.

Calcium-sensing receptor promotes calcium oxalate crystal adhesion and renal injury in Wistar rats by promoting ROS production and subsequent regulation of PS ectropion, OPN, KIM-1, and ERK expression

OBJECTIVES

To explore the mechanism of calcium-sensing receptors (CaSRs) during the development of nephrolithiasis.

MATERIALS AND METHODS

Wistar rats were treated with ethylene glycol to induce calcium oxalate crystallization, and gadolinium chloride (GdCl₃, an agonist of CaSR) and NPS 2390 (an antagonist of CaSR) were added. Oxidative stress (OS) and calcium oxalate crystals in the kidney were observed. CaSR expression and the expression of extracellular signal-regulated protein kinase (ERK), OPN, and KIM-1 were determined by western blotting. In addition, renal tubular epithelial cells were isolated from the kidney to observe phosphatidylserine (PS) ectropion using flow cytometric analysis. Various biochemical parameters were assessed in serum and urine at the end of the experiment.

RESULTS

Calcium oxalate increased OS, crystal adhesion, PS ectropion, and the expression of CaSR and ERK, OPN, and KIM-1 in vivo. In addition, lower levels of urine citrate as well as increased serum creatinine and urea levels were observed after treatment with calcium oxalate (p < .05). Compared with calcium oxalate treatment alone, the above deleterious changes were further significantly confirmed by GdCl₃ but were reversed by NPS-2390. However, urine calcium excretion was decreased after ethylene glycol treatment but was significantly reduced by NPS 2390 and increased by GdCl₃ (p < .05).

CONCLUSIONS

The results suggest that CaSR might play significant roles in the induction of nephrolithiasis in rats by regulating reactive oxygen species (ROS) and PS ectropion and the composition of urine, OPN, KIM-1, and ERK expression.

Calcium-Sensing Receptor and Regulation of WNK Kinases in the Kidney

The kidney is essential for systemic calcium homeostasis. Urinary calcium excretion can be viewed as an integrative renal response to endocrine and local stimuli. The extracellular calcium-sensing receptor (CaSR) elicits a number of adaptive reactions to increased plasma Ca²⁺ levels including the control of parathyroid hormone release and regulation of the renal calcium handling. Calcium reabsorption in the distal nephron of the kidney is functionally coupled to sodium transport. Apart from Ca²⁺ transport systems, CaSR signaling affects relevant distal Na⁺-(K⁺)-2Cl^- cotransporters, NKCC2 and NCC. NKCC2 and NCC are activated by a kinase cascade comprising with-no-lysine [K] kinases (WNKs) and two homologous Ste20-related kinases, SPAK and OSR1. Gain-of-function mutations within the WNK-SPAK/OSR1-NKCC2/NCC pathway lead to renal salt retention and hypertension, whereas loss-of-function mutations have been associated with salt-losing tubulopathies such as Bartter or Gitelman syndromes. A Bartter-like syndrome has been also described in patients carrying gain-of-function mutations in the CaSR gene. Recent work suggested that CaSR signals via the WNK-SPAK/OSR1 cascade to modulate salt reabsorption along the distal nephron. The review presented here summarizes the latest progress in understanding of functional interactions between CaSR and WNKs and their potential impact on the renal salt handling and blood pressure.

Mechanism of tanshinones and phenolic acids from Danshen in the treatment of coronary heart disease based on co-expression network

Background

The tanshinones and phenolic acids in Salvia miltiorrhiza (also named Danshen) have been confirmed for the treatment of coronary heart disease (CHD), but the action mechanisms remain elusive.

Methods

In the current study, the co-expression protein interaction network (Ce-PIN) was used to illustrate the differences between the tanshinones and phenolic acids of Danshen in the treatment of CHD. By integrating the gene expression profile data and protein-protein interactions (PPIs) data, the Ce-PINs of tanshinones and phenolic acids were constructed. Then, the Ce-PINs were analyzed by gene ontology enrichment analyzed based on the optimal algorithm.

Results

It turned out that Danshen is able to treat CHD by regulating the blood circulation, immune response and lipid metabolism. However, phenolic acids may regulate the blood circulation by Extracellular calcium-sensing receptor (CaSR), Endothelin-1 receptor (EDNRA), Endothelin-1 receptor (EDNRB), Kininogen-1 (KNG1), tanshinones may regulate the blood circulation by Guanylate cyclase soluble subunit alpha-1 (GUCY1A3) and Guanylate cyclase soluble subunit beta-1 (GUCY1B3). In addition, both the phenolic acids and tanshinones may regulate the immune response or inflammation by T-cell surface glycoprotein CD4 (CD4), Receptor-type tyrosine-protein phosphatase C (PTPRC).

Conclusion

Through the same targets of the same biological process and different targets of the same biological process, the tanshinones and phenolic acids synergistically treat coronary heart disease.

Plasma total calcium concentration is associated with blood pressure and systemic vascular resistance in normotensive and never-treated hypertensive subjects

Purpose: The underlying causes of primary hypertension are not fully understood. Evidence on the relation of plasma calcium concentration with blood pressure (BP) is inconsistent and relies largely on studies utilizing office BP measurements in populations using cardiovascular drugs. In many studies adjustment for confounders was not optimal. In this cross-sectional study we examined the association of plasma total calcium concentration with the haemodynamic determinants of blood pressure.Subjects and methods: Supine haemodynamics were recorded using pulse wave analysis, whole-body impedance cardiography, and heart rate variability analysis in 618 normotensive or never-treated hypertensive subjects (aged 19-72 years) without diabetes, cardiovascular or renal disease, or cardiovascular medications. Linear regression analysis was used to investigate factors associated with haemodynamic variables.Results: Mean age was 45.0 years, body mass index 26.8 kg/m², seated office BP 141/89 mmHg, and 307 subjects (49.7%) were male. Mean values of routine blood and plasma chemistry analyses were within the reference limits of the tests except for low-density lipoprotein cholesterol (3.05 mmol/l). In the laboratory, mean supine radial BP was 131/75 mmHg, and both systolic and diastolic BP correlated directly with plasma total calcium concentration (r = 0.25 and r = 0.22, respectively, p < 0.001 for both). In regression analysis plasma total calcium concentration was an independent explanatory variable for radial and aortic systolic and diastolic BP, and systemic vascular resistance, but not for cardiac output, pulse wave velocity, or any of the heart rate variability parameters.Conclusion: Plasma total calcium concentration was directly associated with systolic and diastolic BP and systemic vascular resistance in normotensive or never-treated hypertensive subjects without comorbidities and cardiovascular medications. Higher plasma calcium concentration potentially plays a role in primary hypertension via an effect on vascular resistance.

CaSR participates in the regulation of vascular tension in the mesentery of hypertensive rats via the PLC‑IP3/AC‑V/cAMP/RAS pathway

Hypertension is a cardiovascular disease that severely impairs human health; however, its specific etiology and pathogenesis are complex. The present study investigated the effects of the calcium sensing receptor (CaSR) on vascular tone in spontaneously hypertensive rats (SHRs), and clarified the role and mechanism of CaSR in regulating this property with respect to the phospholipase C (PLC)-inositol 1,4,5-triphosphate (IP₃)/adenylate cyclase-V(AC-V)/cyclic adenosine monophosphate (cAMP)/renin-angiotensin system (RAS) pathway in these animals. CaSR protein expression in the mesenteric artery (MA) of rats and CaSR protein expression in SHRs were significantly reduced. Based on wire myography studies, vasoconstriction was significantly augmented and vasodilatation was attenuated in SHRs, and this effect was endothelium-independent. The CaSR calcimimetic NPSR568 and inhibitor NPS2143 reduced vasoconstriction and enhanced vasodilation in SHRs. Furthermore, pretreatment with PLC-IP₃/AC-V/cAMP/RAS pathway blockers significantly reduced the vasoconstriction response and enhanced the vasodilator response in SHRs and Wistar-Kyoto rats (WKY), and these effects were partially dependent on the endothelium. Additionally, pretreatment with CaSR inhibitors were determined to cooperate with the PLC-IP₃/AC-V/cAMP/RAS pathway inhibitors to significantly reduce vasoconstriction and enhance vasodilation in SHRs and WKY. Our results demonstrated that CaSR is functionally expressed in the MA of SHRs, and that CaSR expression is decreased in SHRs. Additionally, vasoconstriction was enhanced while vasodilatation was attenuated in SHRs; these processes were determined to be endothelium-independent. CaSR is involved in the regulation of blood pressure and vascular tension in SHRs and WKYs. In association with mechanistic differences, this effect was proposed to be partially endothelium-dependent and mediated by the PLC-IP₃/AC-V/cAMP/RAS pathway.

Calcimimetic R-568 vasodilatory effect on mesenteric vascular beds from normotensive (WKY) and spontaneously hypertensive (SHR) rats. Potential involvement of vascular smooth muscle cells (vSMCs)

The potential role of calcimimetics as vasculotropic agents has been suggested since the discovery that calcium sensing receptors (CaSRs) are expressed in cardiovascular tissues. However, whether this effect is CaSR-dependent or -independent is still unclear. In the present study the vascular activity of calcimimetic R-568 was investigated in mesenteric vascular beds (MVBs) isolated from Spontaneously Hypertensive rats (SHR) and the relative age-matched Wistar-Kyoto (WKY) control rats. Pre-constricted MBVs were perfused with increasing concentrations of R-568 (10 nM– 30 μM) resulting in a rapid dose-dependent vasodilatation. However, in MVBs from SHR this was preceded by a small but significant vasoconstriction at lowest nanomolar concentrations used (10–300 nM). Pre-treatment with pharmacological inhibitors of nitric oxide (NO) synthase (NOS, L-NAME), K_Ca channels (CTX), cyclo-oxygenase (INDO) and CaSR (Calhex) or the endothelium removal suggest that NO, CaSR and the endothelium itself contribute to the R-568 vasodilatory/vasoconstrictor effects observed respectively in WKY/SHR MVBs. Conversely, the vasodilatory effects resulted by highest R-568 concentration were independent of these factors. Then, the ability of lower R-568 doses (0.1–1 μM) to activate endothelial-NOS (eNOS) pathway in MVBs homogenates was evaluated. The Akt and eNOS phosphorylation levels resulted increased in WKY homogenates and Calhex significantly blocked this effect. Notably, this did not occur in the SHR. Similarly, vascular smooth muscle cells (vSMCs) stimulation with lower R-568 doses resulted in Akt activation and increased NO production in WKY but not in SHR cells. Interestingly, in these cells this was associated with the absence of the biologically active dimeric form of the CaSR thus potentially contributing to explain the impaired vasorelaxant effect observed in response to R-568 in MVB from SHR compared to WKY. Overall, these findings provide new insight on the mechanisms of action of the calcimimetic R-568 in modulating vascular tone both in physiological and pathological conditions such as hypertension.

Calcium sensing receptor expression and signalling in cardiovascular physiology and disease

Initially identified in the parathyroidea, the calcium sensing receptor (CaSR) is now recognized as an ubiquitously expressed receptor that exerts specific functions in multiple organs including the cardiovascular system. This review will focus on the role that CaSR plays in vascular and cardiac tissues. In the vasculature, CaSR is expressed in endothelial and smooth muscle cells. CaSR of endothelial cells participates in part to the regulation of local perfusion by linkage of CaSR activation to endothelial hyperpolarization and nitric oxide release. CaSR of smooth muscle cells is involved in the control of proliferation. In the pulmonary vasculature, however, CaSR participates in the onset of pulmonary hypertension, making CaSR antagonism a therapeutic option in this case. In the heart, CaSR is expressed in cardiac fibroblasts and myoyctes, contributing to normal cardiac function and composition of extracellular matrix. More important, activation of CaSR may participate in the cardiac protective effects of ischaemic pre-conditioning. In conclusion, CaSR plays an important physiological role in many regulatory pathways of the cardiovascular system, but due to the complex interaction between various cardiovascular cells and cell-specific effects, use of activators or inhibitors of CaSR for treatment of specific disease forms is yet not on the way.

High-Sodium Diet Has Opposing Effects on Mean Arterial Blood Pressure and Cerebral Perfusion in a Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

Cerebral ionic homeostasis impairment, especially Ca2+, has been observed in Alzheimer's disease (AD) and also with hypertension. Hypertension and AD both have been implicated in impaired cerebral autoregulation. However, the relationship between the ionic homeostasis impairment in AD and hypertension and cerebral blood flow (CBF) autoregulation is not clear.

OBJECTIVE

To test the hypothesis that a high-salt diet regimen influences the accumulation of amyloid-β (Aβand CBF) and CBF, exacerbates cognitive decline, and increases the propensity to AD.

METHODS

Double transgenic mice harboring the amyloid-β protein precursor (APPswe), and presenilin-1 (PSEN1) along with control littermates, 2 months of age at initiation of special diet, were divided into 4 groups: Group A, APP/PS1 and Group B, controls fed a high-sodium (4.00%) chow diet for 3 months; Group C, APP/PS1 and Group D, controls fed a low-sodium (0.08%) regular chow diet for 3 months. Mean arterial blood pressure (MAP) and CBF were measured noninvasively using the tail MAP measurement device and magnetic resonance imaging, respectively. Aβ plaques numbers in the cortex and hippocampus of APP/PS1 were quantified.

RESULTS

In contrary to controls, APP/PS1 mice fed a high-salt diet did not show markedly elevated mean systolic and diastolic blood pressure (134±4.8 compared with 162±2.8 mmHg, and 114±5.0 compared with 137±20 mmHg, p< 0.0001). However, a high-salt diet increased CBF in both APP/PS1 and controls and did not alter the cerebral tissue integrity. Aβ plaques were significantly reduced in the cortex and hippocampus of mice fed a high-salt diet.

CONCLUSION

These data suggest that a high-salt diet differently affects MAP and CBF in APP/PS1 mice and controls.

TRPC1 stimulates calcium‑sensing receptor‑induced store‑operated Ca2+ entry and nitric oxide production in endothelial cells

Store-operated Ca²⁺ entry (SOCE) via store-operated Ca²⁺ channels (SOCC), encoded by transient receptor potential canonical (TRPC) channel proteins, is an important underlying mechanism regulating intracellular Ca²⁺ concentration ([Ca²⁺]_i) and various intracellular functions in endothelial cells (ECs). TRPC1, the probable candidate for SOCC, is expressed in ECs. Ca²⁺-sensing receptor (CaSR) is functionally expressed in vascular endothelium and is important in Ca²⁺ mobilization and cardiovascular functions. To date, there have been no reports demonstrating an association between CaSR and TRPC1 in ECs. The present study investigated the effects of TRPC1 on CaSR-induced Ca²⁺ influx and nitric oxide (NO) production in human umbilical vein ECs (HUVECs). TRPC1 and CaSR proteins in HUVECs were measured by immunostaining and western blot analysis. [Ca²⁺]_i levels were measured using the Fura-2-acetoxymethyl ester method. The indicator 3-amino, 4-aminomethyl-2, 7-difluorescein diacetate was used to measure NO production in HUVECs. The expression of TRPC1 protein in HUVECs was silenced by transfecting HUVECs with small interfering RNA (siRNA) against TRPC1. Although changes in extracellular Ca²⁺ failed to alter [Ca²⁺]_i in HUVECs, the CaSR agonist spermine increased [Ca²⁺]_i and NO production in HUVECs. NO production in HUVECs was diminished in Ca²⁺-free medium or following treatment with a CaSR negative allosteric modulator (Calhex231), SOCC inhibitor (MRS1845) or TRPC inhibitor (SKF96365). The spermine-induced increases in [Ca²⁺]_i and NO production were reduced in HUVECs transfected with TRPC1 siRNA. These results suggested that TRPC1 is a primary candidate in forming SOCC that stimulates CaSR-induced SOCE and NO production in HUVECs and is a potential therapeutic target for vascular diseases.

Calcium Oxalate Induces Renal Injury through Calcium-Sensing Receptor

Objective. To investigate whether calcium-sensing receptor (CaSR) plays a role in calcium-oxalate-induced renal injury. Materials and Methods. HK-2 cells and rats were treated with calcium oxalate (CaOx) crystals with or without pretreatment with the CaSR-specific agonist gadolinium chloride (GdCl₃) or the CaSR-specific antagonist NPS2390. Changes in oxidative stress (OS) in HK-2 cells and rat kidneys were assessed. In addition, CaSR, extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal protein kinase (JNK), and p38 expression was determined. Further, crystal adhesion assay was performed in vitro, and the serum urea and creatinine levels and crystal deposition in the kidneys were also examined. Results. CaOx increased CaSR, ERK, JNK, and p38 protein expression and OS in vitro and in vivo. These deleterious changes were further enhanced upon pretreatment with the CaSR agonist GdCl₃ but were attenuated by the specific CaSR inhibitor NPS2390 compared with CaOx treatment alone. Pretreatment with GdCl₃ further increased in vitro and in vivo crystal adhesion and renal hypofunction. In contrast, pretreatment with NPS2390 decreased in vitro and in vivo crystal adhesion and renal hypofunction. Conclusions. CaOx-induced renal injury is related to CaSR-mediated OS and increased mitogen-activated protein kinase (MAPK) signaling, which subsequently leads to CaOx crystal adhesion.

The cardiovascular system in familial hypocalciuric hypercalcemia: a cross-sectional study on physiological effects of inactivating variants in the calcium-sensing receptor gene

OBJECTIVE

Loss-of-function variants in the gene encoding the calcium-sensing receptor (CASR) result in familial hypocalciuric hypercalcemia (FHH), causing hypercalcemia with high normal or elevated parathyroid hormone levels. The CASR may also influence electrolyte and water homeostasis. It is unknown whether FHH affects cardiovascular health. We, therefore investigated whether FHH is associated with changes in the regulation of the cardiovascular system by measuring 24-h blood pressure (BP), arterial stiffness and vasoactive hormones.

DESIGN

Cross-sectional study comparing 50 patients with FHH to age- and gender-matched controls.

RESULTS

Studied subjects (69% women) had a mean age of 56years. A similar number of patients and controls (33%) were on treatment with antihypertensive drugs. Overall, no differences were found between groups in 24-h ambulatory BP or pulse wave velocity. However, compared with controls, diastolic BP during nighttime was lower in FHH females (60±5 vs 66±9mmHg, P<0.01) and higher in FHH males (69±6 vs 64±5mmHg, P=0.02). FHH was associated with a significantly higher plasma osmolality (P<0.01), higher plasma levels of vasopressin (P<0.01) and a higher renal excretion of epithelial sodium channels (ENaCs) (P=0.03), whereas urine aquaporin-2 and plasma sodium, aldosterone and renin did not differ between groups. FHH patients had a lower urinary volume with an increased osmolality if analyses were restricted to those not on treatments with antihypertensive drugs.

CONCLUSIONS

FHH does not seem to be associated with an increased risk of CVD.

Mechanisms by which calcium receptor stimulation modifies electromechanical coupling in isolated ventricular cardiomyocytes

The calcium-sensing receptor (CaR) is widely expressed throughout the entire cardiovascular system and is capable of activating signaling pathways in different cells. Alongside calcium, the CaR also responds to physiological polycations such as putrescine underlining a participation in physiological and pathophysiological processes. Here, we aimed to determine mechanisms as to how CaR activation affects the contractile responsiveness of ventricular cardiomyocytes under basal and stimulated conditions. For that purpose, cardiac myocytes from 3-month-old male Wistar rats were isolated, and the acute effects of an antagonist (NPS2390), agonists (putrescine and gadolinium), or of downregulation of the CaR by siRNA on cell shortening were recorded in a cell-edge-detection system. In addition, experiments were performed on muscle stripes and Langendorff preparations. Mechanistic insights were taken from calcium transients of beating fura-2 AM-loaded cardiomyocytes and western blots. Isolated ventricular cardiomyocytes constitutively express CaR. The expression in the atria is less pronounced. Acute inhibition of CaR reduced basal cell shortening of ventricular myocytes at nearly physiological levels of extracellular calcium. Inhibition of CaR strongly reduced contractility of ventricular muscle stripes but not of atria. Activation of CaR by putrescine and gadolinium influences the contractile responsiveness of isolated cardiomyocytes. Increased calcium mobilization from the sarcoplasmic reticulum via an IP3-dependent mechanism was responsible for amplified systolic calcium transients and a subsequent improvement in cell shortening. Alongside with these effects, activation of CaR increased relaxation velocity of the cells. In conclusion, ventricular CaR expression affects contractile parameters of ventricular heart muscle cells and modifies electromechanical coupling of cardiomyocytes.

The calcium-sensing receptor and calcimimetics in blood pressure modulation

Calcium is a crucial second messenger in the cardiovascular system. However, calcium may also be an extracellular first messenger through a G-protein-coupled receptor that senses extracellular concentration (Ca(2+)(o)), the calcium-sensing receptor (CaR). The most prominent physiological function of the CaR is to maintain the extracellular Ca(2+) level in a very tight range by regulating the circulating levels of parathyroid hormone (PTH). This control over PTH and Ca(2+) levels is partially lost in patients suffering from primary and secondary hyperparathyroidism. Allosteric modulators of the CaR (calcimimetics) are the first drugs in their class to become available for clinical use and have been shown to successfully treat certain forms of primary and secondary hyperparathyroidism. In addition, several studies suggest beneficial effects of calcimimetics on cardiovascular risk factors associated with hyperparathyroidism. Although a plethora of studies demonstrated the CaR in heart and blood vessels, exact roles of the receptor in the cardiovascular system still remain to be elucidated. However, several studies point toward a possibility that the CaR might be involved in the regulation of vascular tone. This review will summarize the current knowledge on the possible functions of the CaR and calcimimetics on blood pressure regulation.

Signaling through the extracellular calcium-sensing receptor (CaSR)

The extracellular calcium ([Formula: see text])-sensing receptor (CaSR) was the first GPCR identified whose principal physiological ligand is an ion, namely extracellular Ca(2+). It maintains the near constancy of [Formula: see text] that complex organisms require to ensure normal cellular function. A wealth of information has accumulated over the past two decades about the CaSR's structure and function, its role in diseases and CaSR-based therapeutics. This review briefly describes the CaSR and key features of its structure and function, then discusses the extracellular signals modulating its activity, provides an overview of the intracellular signaling pathways that it controls, and, finally, briefly describes CaSR signaling both in tissues participating in [Formula: see text] homeostasis as well as those that do not. Factors controlling CaSR signaling include various factors affecting the expression of the CaSR gene as well as modulation of its trafficking to and from the cell surface. The dimeric cell surface CaSR, in turn, links to various heterotrimeric and small molecular weight G proteins to regulate intracellular second messengers, lipid kinases, various protein kinases, and transcription factors that are part of the machinery enabling the receptor to modulate the functions of the wide variety of cells in which it is expressed. CaSR signaling is impacted by its interactions with several binding partners in addition to signaling elements per se (i.e., G proteins), including filamin-A and caveolin-1. These latter two proteins act as scaffolds that bind signaling components and other key cellular elements (e.g., the cytoskeleton). Thus CaSR signaling likely does not take place randomly throughout the cell, but is compartmentalized and organized so as to facilitate the interaction of the receptor with its various signaling pathways.

Calcium-sensing receptor modulates extracellular Ca(2+) entry via TRPC-encoded receptor-operated channels in human aortic smooth muscle cells

Ca-sensing receptor (CaSR), a member of the G protein-coupled receptor family, regulates the synthesis of parathyroid hormone in response to changes in serum Ca(2+) concentrations. The functions of CaSR in human vascular smooth muscle cells are largely unknown. Here we sought to study CaSR activation and the underlying molecular mechanisms in human aortic smooth muscle cells (HASMC). Extracellular Ca(2+) ([Ca(2+)](o)) dose-dependently increased free cytosolic Ca(2+) ([Ca(2+)](cyt)) in HASMC, with a half-maximal response (EC(50)) of 0.52 mM and a Hill coefficient of 5.50. CaSR was expressed in HASMC, and the [Ca(2+)](o)-induced [Ca(2+)](cyt) rise was abolished by dominant negative mutants of CaSR. The CaSR-mediated increase in [Ca(2+)](cyt) was also significantly inhibited by pertussis toxin, the phospholipase C inhibitor U-73122, or the general protein kinase C (PKC) inhibitor chelerythrine, but not by the conventional PKC inhibitor, Gö6976. Depletion of membrane cholesterol by pretreatment with methyl-β-cyclodextrin markedly decreased CaSR-induced increase in [Ca(2+)](cyt). Blockade of TRPC channels with 2-aminoethoxydiphenyl borate, SKF-96365, or La(3) significantly inhibited [Ca(2+)](o) entry, whereas activation of TRPC6 channels with flufenamic acid potentiated [Ca(2+)](o) entry. Neither cyclopiazonic acid nor caffeine or ionomycin had any effect on [Ca(2+)](cyt) in [Ca(2+)](o)-free solutions. TRPC6 and PKCε mRNA and proteins were detected in HASMC, and [Ca(2+)](o) induced PKCε phosphorylation, which could be prevented by chelerythrine. Our data suggest that CaSR activation mediates [Ca(2+)](o) entry, likely through TRPC6-encoded receptor-operated channels that are regulated by a PLC/PKCε cascade. Our study therefore provides evidence not only for functional expression of CaSR, but also for a novel pathway whereby it regulates [Ca(2+)](o) entry in HASMC.

Novel calcium sensing receptor ligands: a patent survey

INTRODUCTION

In the parathyroid gland, the calcium sensing receptor responds to small changes in circulating levels of Ca(2+), and consequently stimulates or inhibits the secretion of parathyroid hormone (PTH). Thus, ligands potentiating the action of calcium (calcimimetics) lead to decreased PTH secretion and can thus be useful for the treatment of hyperparathyroidism. On the other hand, ligands which antagonize the action of calcium (calcilytics) stimulate PTH secretion, favoring bone tissue regeneration.

AREAS COVERED

This review first discusses the rapid development of calcimimetics (only one of which has been approved for the treatment of hyperparathyroidism) followed by that of calcilytics (none of which has as yet been approved for the treatment of osteoporosis). Peer-reviewed articles generated by these patents are also surveyed.

EXPERT OPINION

The rapid progress in developing a clinically approved calcimimetic has not been matched by an identical success in finding an orally available calcilytic useful for the treatment of osteoporosis. However, the growing importance of osteoporosis as a debilitating disease is a stimulating factor in discovering such compounds.

Relationship between dietary sodium, potassium, and calcium, anthropometric indexes, and blood pressure in young and middle aged Korean adults

Epidemiological evidence of the effects of dietary sodium, calcium, and potassium, and anthropometric indexes on blood pressure is still inconsistent. To investigate the relationship between dietary factors or anthropometric indexes and hypertension risk, we examined the association of systolic and diastolic blood pressure (SBP and DBP) with sodium, calcium, and potassium intakes and anthropometric indexes in 19~49-year-olds using data from Korean National Health and Nutrition Examination Survey (KNHANES) III. Total of 2,761 young and middle aged adults (574 aged 19~29 years and 2,187 aged 30~49 years) were selected from KNHANES III. General information, nutritional status, and anthropometric data were compared between two age groups (19~29 years old and 30~49 years old). The relevance of blood pressure and risk factors such as age, sex, body mass index (BMI), weight, waist circumference, and the intakes of sodium, potassium, and calcium was determined by multiple regression analysis. Multiple regression models showed that waist circumference, weight, and BMI were positively associated with SBP and DBP in both age groups. Sodium and potassium intakes were not associated with either SBP or DBP. Among 30~49-year-olds, calcium was inversely associated with both SBP and DBP (P = 0.012 and 0.010, respectively). Our findings suggest that encouraging calcium consumption and weight control may play an important role in the primary prevention and management of hypertension in early adulthood.

EDHF: an update

The endothelium controls vascular tone not only by releasing NO and prostacyclin, but also by other pathways causing hyperpolarization of the underlying smooth muscle cells. This characteristic was at the origin of the term 'endothelium-derived hyperpolarizing factor' (EDHF). However, this acronym includes different mechanisms. Arachidonic acid metabolites derived from the cyclo-oxygenases, lipoxygenases and cytochrome P450 pathways, H(2)O(2), CO, H(2)S and various peptides can be released by endothelial cells. These factors activate different families of K(+) channels and hyperpolarization of the vascular smooth muscle cells contribute to the mechanisms leading to their relaxation. Additionally, another pathway associated with the hyperpolarization of both endothelial and vascular smooth muscle cells contributes also to endothelium-dependent relaxations (EDHF-mediated responses). These responses involve an increase in the intracellular Ca(2+) concentration of the endothelial cells, followed by the opening of SK(Ca) and IK(Ca) channels (small and intermediate conductance Ca(2+)-activated K(+) channels respectively). These channels have a distinct subcellular distribution: SK(Ca) are widely distributed over the plasma membrane, whereas IK(Ca) are preferentially expressed in the endothelial projections toward the smooth muscle cells. Following SK(Ca) activation, smooth muscle hyperpolarization is preferentially evoked by electrical coupling through myoendothelial gap junctions, whereas, following IK(Ca) activation, K(+) efflux can activate smooth muscle Kir2.1 and/or Na(+)/K(+)-ATPase. EDHF-mediated responses are altered by aging and various pathologies. Therapeutic interventions can restore these responses, suggesting that the improvement in the EDHF pathway contributes to their beneficial effect. A better characterization of EDHF-mediated responses should allow the determination of whether or not new drugable targets can be identified for the treatment of cardiovascular diseases.