The functional expression of extracellular calcium-sensing receptor in rat pulmonary artery smooth muscle cells

Stimulation of the calcium-sensing receptor induces relaxations through CGRP and NK1 receptor-mediated pathways in male rat mesenteric arteries

Stimulation of the calcium-sensing receptor (CaSR) regulates vascular contractility, but cellular mechanisms involved remain unclear. This study investigated the role of perivascular sensory nerves in CaSR-induced relaxations of male rat mesenteric arteries. In fluorescence studies, colocalisation between synaptophysin, a synaptic vesicle marker, and the CaSR was present in the adventitial layer of arterial segments. Using wire myography, increasing external Ca2+ concentration ([Ca2+]o) from 1 to 10 mM induced vasorelaxations, previously shown to involve the CaSR, which were inhibited by pretreatment with capsaicin. [Ca2+]o-induced vasorelaxations were partially reduced by the calcitonin gene-related peptide (CGRP) receptor blockers, CGRP 8-37 and BIBN 4096, and the neurokinin 1 (NK1) receptor blocker L733,060. The inhibitory effect of CGRP 8-37 required a functional endothelium whereas the inhibitory action of L733,060 did not. Complete inhibition of [Ca2+]o-induced vasorelaxations occurred when CGRP 8-37 and L733,060 were applied together. [Ca2+]o-induced vasorelaxations in the presence of capsaicin were abolished by the ATP-dependent K+ channel (KATP) blocker PNU 37883, but unaffected by the endothelium nitric oxide synthase (eNOS) inhibitor L-NAME. We suggest that the CaSR on perivascular sensory nerves mediate relaxations in rat mesenteric arteries via endothelium-dependent and -independent mechanisms involving CGRP and NK1 receptor-activated NO production and KATP channels, respectively.

Stimulation of the calcium-sensing receptor induces relaxations of rat mesenteric arteries by endothelium-dependent and -independent pathways via BKCa and KATP channels

Stimulation of the calcium-sensing receptor (CaSR) induces both vasoconstrictions and vasorelaxations but underlying cellular processes remain unclear. This study investigates expression and effect of stimulating the CaSR by increasing external Ca2+ concentration ([Ca2+ ]o ) on contractility of rat mesenteric arteries. Immunofluorescence studies showed expression of the CaSR in perivascular nerves, vascular smooth muscle cells (VSMCs), and vascular endothelium cells. Using wire myography, increasing [Ca2+ ]o from 1 to 10 mM induced vasorelaxations which were inhibited by the calcilytic Calhex-231 and partially dependent on a functional endothelium. [Ca2+ ]o -induced vasorelaxations were reduced by endothelial NO synthase (eNOS, L-NAME) and large conductance Ca2+ -activated K+ channels (BKCa , iberiotoxin), with their inhibitory action requiring a functional endothelium. [Ca2+ ]o -induced vasorelaxations were also markedly inhibited by an ATP-dependent K+ channel (KATP ) blocker (PNU37883), which did not require a functional endothelium to produce its inhibitory action. Inhibitor studies also suggested contributory roles for inward rectifying K+ channels (Kir ), Kv7 channels, and small conductance Ca2+ -activated K+ channels (SKCa ) on [Ca2+ ]o -induced vasorelaxations. These findings indicate that stimulation of the CaSR mediates vasorelaxations involving multiple pathways, including an endothelium-dependent pathway involving NO production and activation of BKCa channels and an endothelium-independent pathway involving stimulation of KATP channels.

The CaSR/TRPV4 coupling mediates pro-inflammatory macrophage function

AIM

Although calcium-sensing receptor (CaSR) and transient receptor potential vanilloid 4 (TRPV4) channels are functionally expressed on macrophages, it is unclear if they work coordinately to mediate macrophage function. The present study investigates whether CaSR couples to TRPV4 channels and mediates macrophage polarization via Ca²⁺ signaling.

METHODS

The role of CaSR/TRPV4/Ca²⁺ signaling was assessed in lipopolysaccharide (LPS)-treated peritoneal macrophages (PMs) from wild-type (WT) and TRPV4 knockout (TRPV4 KO) mice. The expression and function of CaSR and TRPV4 in PMs were analyzed by immunofluorescence and digital Ca²⁺ imaging. The correlation factors of M1 polarization, CCR7, IL-1β, and TNFα were detected using q-PCR, western blot, and ELISA.

RESULTS

We found that PMs expressed CaSR and TRPV4, and CaSR activation-induced marked Ca²⁺ signaling predominately through extracellular Ca²⁺ entry, which was inhibited by selective pharmacological blockers of CaSR and TRPV4 channels. The CaSR activation-induced Ca²⁺ signaling was significantly attenuated in PMs from TRPV4 KO mice compared to those from WT mice. Moreover, the CaSR activation-induced Ca²⁺ entry via TRPV4 channels was inhibited by blocking phospholipases A2 (PLA2)/cytochromeP450 (CYP450) and phospholipase C (PLC)/Protein kinase C (PKC) pathways. Finally, CaSR activation promoted the expression and release of M1-associated cytokines IL-1β and TNFɑ, which were attenuated in PMs from TRPV4 KO mice.

CONCLUSION

We reveal a novel coupling of the CaSR and TRPV4 channels via PLA2/CYP450 and PLC/PKC pathways, promoting a Ca²⁺ -dependent M1 macrophage polarization. Modulation of this coupling and downstream pathways may become a potential strategy for the prevention/treatment of immune-related disease.

Extracellular Calcium Receptor as a Target for Glutathione and Its Derivatives

Extracellular glutathione (GSH) and oxidized glutathione (GSSG) can modulate the function of the extracellular calcium sensing receptor (CaSR). The CaSR has a binding pocket in the extracellular domain of CaSR large enough to bind either GSH or GSSG, as well as the naturally occurring oxidized derivative L-cysteine glutathione disulfide (CySSG) and the compound cysteinyl glutathione (CysGSH). Modeling the binding energies (ΔG) of CySSG and CysGSH to CaSR reveals that both cysteine derivatives may have greater affinities for CaSR than either GSH or GSSG. GSH, CySSG, and GSSG are found in circulation in mammals and, among the three, CySSG is more affected by HIV/AIDs and aging than either GSH or GSSG. The beta-carbon linkage of cysteine in CysGSH may model a new class of calcimimetics, exemplified by etelcalcetide. Circulating glutathionergic compounds, particularly CySSG, may mediate calcium-regulatory responses via receptor-binding to CaSR in a variety of organs, including parathyroids, kidneys, and bones. Receptor-mediated actions of glutathionergics may thus complement their roles in redox regulation and detoxification. The glutathionergic binding site(s) on CaSR are suggested to be a target for development of drugs that can be used in treating kidney and other diseases whose mechanisms involve CaSR dysregulation.

Platelet-derived growth factor-BB induces pulmonary venous smooth muscle cells proliferation by upregulating calcium sensing receptor under hypoxic conditions

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling, which exists in both pulmonary arteries and pulmonary veins. Pulmonary vascular remodeling stems from excessive proliferation of pulmonary vascular myocytes. Platelet-derived growth factor-BB (PDGF-BB) is a vital vascular regulator whose level increases in PH human lungs. Although the mechanisms by which pulmonary arterial smooth muscle cells respond to PDGF-BB have been studied extensively, the effects of PDGF-BB on pulmonary venous smooth muscle cells (PVSMCs) remain unknown. We herein examined the involvement of calcium sensing receptor (CaSR) in PDGF-BB-induced PVSMCs proliferation under hypoxic conditions. In PVSMCs isolated from rat intrapulmonary veins, PDGF-BB increased the cell number and DNA synthesis under normoxic and hypoxic conditions, which was accompanied by upregulated CaSR expression. The influences of PDGF-BB on proliferation and CaSR expression in hypoxic PVSMCs were greater than that in normoxic PVSMCs. In hypoxic PVSMCs superfused with Ca²⁺-free solution, restoration of extracellular Ca²⁺ induced an increase of [Ca²⁺]_i, which was significantly smaller than that in PDGF-BB-treated hypoxic PVSMCs. The positive CaSR modulator spermine enhanced, whereas the negative CaSR modulator NPS2143 attenuated, the extracellular Ca²⁺-induced [Ca²⁺]_i increase in PDGF-BB-treated hypoxic PVSMCs. Furthermore, the spermine enhanced, whereas the NPS2143 inhibited, PDGF-BB-induced proliferation in hypoxic PVSMCs. Silencing CaSR with siRNA attenuated the extracellular Ca²⁺-induced [Ca²⁺]_i increase in PDGF-BB-treated hypoxic PVSMCs and inhibited PDGF-BB-induced proliferation in hypoxic PVSMCs. In conclusion, these results demonstrated that CaSR mediating PDGF-BB-induced excessive PVSMCs proliferation is an important mechanism involved in the initiation and progression of PVSMCs proliferation under hypoxic conditions.

The Nitric Oxide Pathway in Pulmonary Arterial Hypertension: Pathomechanism, Biomarkers and Drug Targets

The altered Nitric Oxide (NO) pathway in the pulmonary endothelium leads to increased vascular smooth muscle tone and vascular remodelling, and thus contributes to the development and progression of pulmonary arterial hypertension (PAH). The pulmonary NO signalling is abrogated by the decreased expression and dysfunction of the endothelial NO synthase (eNOS) and the accumulation of factors blocking eNOS functionality. The NO deficiency of the pulmonary vasculature can be assessed by detecting nitric oxide in the exhaled breath or measuring the degradation products of NO (nitrite, nitrate, S-nitrosothiol) in blood or urine. These non-invasive biomarkers might show the potential to correlate with changes in pulmonary haemodynamics and predict response to therapies. Current pharmacological therapies aim to stimulate pulmonary NO signalling by suppressing the degradation of NO (phosphodiesterase- 5 inhibitors) or increasing the formation of the endothelial cyclic guanosine monophosphate, which mediates the downstream effects of the pathway (soluble guanylate cyclase sensitizers). Recent data support that nitrite compounds and dietary supplements rich in nitrate might increase pulmonary NO availability and lessen vascular resistance. This review summarizes current knowledge on the involvement of the NO pathway in the pathomechanism of PAH, explores novel and easy-to-detect biomarkers of the pulmonary NO.

Calcium-sensing receptor in the development and treatment of pulmonary hypertension

Calcium-sensing receptor (CaSR) is widely involved in the cell proliferation, differentiation, migration, adhesion and apoptosis, which can affect the vascular remodeling in the humanbody. The main ligand of CaSR is extracellular Ca²⁺. CaSR has the physiological significance in Ca²⁺ homeostasis. Pulmonary vascular remodeling is one of the main histopathological changes of pulmonary hypertension (PH). The abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) results in the pulmonary vascular remodeling. CaSR is an important regulator of [Ca²⁺]_i. [Ca²⁺]_i is the main cause of the excessive pulmonary vascular remodeling in patients with PH. In this review, it was conclued that the structure of CaSR was prone to explore the devolopment or the treatment of PH. It was found that the regulation of CaSR with some miRNA could inhibit the proliferation of PASMCs, and that CaSR could affect the occurrence of autophagy in PH. Therefore, CaSR would become a new therapeutic target to PH.

Heteromeric TRPV4/TRPC1 channels mediate calcium-sensing receptor-induced relaxations and nitric oxide production in mesenteric arteries: comparative study using wild-type and TRPC1-/- mice

We have previously provided pharmacological evidence that stimulation of calcium-sensing receptors (CaSR) induces endothelium-dependent relaxations of rabbit mesenteric arteries through activation of heteromeric TRPV4/TRPC1 channels and nitric oxide (NO) production. The present study further investigates the role of heteromeric TRPV4/TRPC1 channels in these CaSR-induced vascular responses by comparing responses in mesenteric arteries from wild-type (WT) and TRPC1^-/- mice. In WT mice, stimulation of CaSR induced endothelium-dependent relaxations of pre-contracted tone and NO generation in endothelial cells (ECs), which were inhibited by the TRPV4 channel blocker RN1734 and the TRPC1 blocking antibody T1E3. In addition, TRPV4 and TRPC1 proteins were colocalised at, or close to, the plasma membrane of endothelial cells (ECs) from WT mice. In contrast, in TRPC1^-/- mice, CaSR-mediated vasorelaxations and NO generation were greatly reduced, unaffected by T1E3, but blocked by RN1734. In addition, the TRPV4 agonist GSK1016790A (GSK) induced endothelium-dependent vasorelaxations which were blocked by RN1734 and T1E3 in WT mice, but only by RN1734 in TRPC1^-/- mice. Moreover, GSK activated cation channel activity with a 6pS conductance in WT ECs but with a 52 pS conductance in TRPC1^-/- ECs. These results indicate that stimulation of CaSR activates heteromeric TRPV4/TRPC1 channels and NO production in ECs, which are responsible for endothelium-dependent vasorelaxations. This study also suggests that heteromeric TRPV4-TRPC1 channels may form the predominant TRPV4-containing channels in mouse mesenteric artery ECs. Together, our data further implicates CaSR-induced pathways and heteromeric TRPV4/TRPC1 channels in the regulation of vascular tone.

GPCRs in pulmonary arterial hypertension: tipping the balance

Pulmonary arterial hypertension (PAH) is a progressive, fatal disease characterised by increased pulmonary vascular resistance and excessive proliferation of pulmonary artery smooth muscle cells (PASMC). GPCRs, which are attractive pharmacological targets, are important regulators of pulmonary vascular tone and PASMC phenotype. PAH is associated with the altered expression and function of a number of GPCRs in the pulmonary circulation, which leads to the vasoconstriction and proliferation of PASMC and thereby contributes to the imbalance of pulmonary vascular tone associated with PAH; drugs targeting GPCRs are currently used clinically to treat PAH and extensive preclinical work supports the utility of a number of additional GPCRs. Here we review how GPCR expression and function changes with PAH and discuss why GPCRs continue to be relevant drug targets for the disease.

Stromal Cell-Derived Factor-1α Alleviates Calcium-Sensing Receptor Activation-Mediated Ischemia/Reperfusion Injury by Inhibiting Caspase-3/Caspase-9-Induced Cell Apoptosis in Rat Free Flaps

Surgical flaps are frequently affected by ischemia/reperfusion (I/R) injury. Calcium-sensing receptor (CaSR) and stromal cell-derived factor-1α (SDF-1α) are closely associated with myocardial I/R injury. This study was performed to evaluate the feasibility of applying SDF-1α to counteract CaSR activation-mediated I/R injury in ischemic free flaps. Free flaps that underwent ischemia for 3 h were equally randomized into five groups: CaCl₂, NPS2143 + CaCl₂, SDF-1α + CaCl₂, AMD3100 + SDF-1α + CaCl₂, and normal saline. The free flaps were harvested to evaluate flap necrosis and neovascularization after 2 h or 7 d of reperfusion. p-CaSR/CaSR was extensively expressed in vascular endothelial cells of free flaps after I/R injury, and activation of the SDF-1α/CXCR4 axis and NPS2143 could reduce the expression of cleaved caspase-3, caspase-9, FAS, Cyt-c, and Bax and increase Bcl-2 expression; the opposite was true after CaSR activation. Interestingly, initiation of the SDF-1α/CXCR4 axis might abrogate CaSR activation-induced I/R injury through enhancement of microvessel density. In conclusion, CaSR might become a novel therapeutic target of free flaps affected by I/R injury. Activation of the SDF-1α/CXCR4 axis and NPS2143 could counteract CaSR activation-mediated I/R injury and promote free flap survival through inhibition of caspase-3/caspase-9-related cell apoptosis and enhancement of neovascularization.

Heteromeric TRPV4/TRPC1 channels mediate calcium-sensing receptor-induced nitric oxide production and vasorelaxation in rabbit mesenteric arteries

Stimulation of calcium-sensing receptors (CaSR) by increasing the external calcium concentration (Ca^2 +]_o) induces endothelium-dependent vasorelaxation through nitric oxide (NO) production and activation of intermediate Ca^2 +-activated K⁺ currents (IK_Ca) channels in rabbit mesenteric arteries. The present study investigates the potential role of heteromeric TRPV4-TRPC1 channels in mediating these CaSR-induced vascular responses. Immunocytochemical and proximity ligation assays showed that TRPV4 and TRPC1 proteins were expressed and co-localised at the plasma membrane of freshly isolated endothelial cells (ECs). In wire myography studies, increasing [Ca^2 +]_o between 1 and 6 mM induced concentration-dependent relaxations of methoxamine (MO)-induced pre-contracted tone, which were inhibited by the TRPV4 antagonists RN1734 and HC067047, and the externally-acting TRPC1 blocking antibody T1E3. In addition, CaSR-evoked NO production in ECs measured using the fluorescent NO indicator DAF-FM was reduced by RN1734 and T1E3. In contrast, [Ca^2 +]_o-evoked perforated-patch IK_Ca currents in ECs were unaffected by RN1734 and T1E3. The TRPV4 agonist GSK1016790A (GSK) induced endothelium-dependent relaxation of MO-evoked pre-contracted tone and increased NO production, which were inhibited by the NO synthase inhibitor L-NAME, RN1734 and T1E3. GSK activated 6pS cation channel activity in cell-attached patches from ECs which was blocked by RN1734 and T1E3. These findings indicate that heteromeric TRPV4-TRPC1 channels mediate CaSR-induced vasorelaxation through NO production but not IK_Ca channel activation in rabbit mesenteric arteries. This further implicates CaSR-induced pathways and heteromeric TRPV4-TRPC1 channels in regulating vascular tone.

The calcilytics Calhex-231 and NPS 2143 and the calcimimetic Calindol reduce vascular reactivity via inhibition of voltage-gated Ca2+ channels

The present study investigates the effect of commonly used negative and positive allosteric modulators of the calcium-sensing receptor (CaSR) on vascular reactivity. In wire myography studies, increasing [Ca2+]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine-induced pre-contracted rabbit mesenteric arteries, with 6mM [Ca2+]o producing almost complete relaxation. [Ca2+]o-induced relaxations were attenuated in the presence of the calcilytics Calhex-231 and NPS 2143, and abolished by the removal of the endothelium. In addition to their calcilytic effects, Calhex-231 and NPS 2143 also produced concentration-dependent inhibitions of methoxamine- or KCl-induced precontracted tone, which were unaffected by removal of the endothelium and unopposed in the presence of the calcimimetic Calindol. In vessels with depleted Ca2+ stores, contractions mediated by Ca2+ influx via voltage-gated Ca2+ channels (VGCCs) were inhibited by Calhex231. In freshly isolated single rabbit mesenteric artery smooth muscle cells, Calhex-231 and NPS 2143 inhibited whole-cell VGCC currents. Application of Calindol also inhibited methoxamine- and KCl-induced pre-contracted tone, and inhibited whole-cell VGCC currents. In conclusion, in addition to their CaSR-mediated actions in the vasculature, Calhex-231, NPS 2143 and Calindol reduce vascular contractility via direct inhibition of VGCCs.

Stimulation of calcium-sensing receptors induces endothelium-dependent vasorelaxations via nitric oxide production and activation of IKCa channels

Stimulation of vascular calcium-sensing receptors (CaSRs) is reported to induce both constrictions and relaxations. However, cellular mechanisms involved in these responses remain unclear. The present study investigates the effect of stimulating CaSRs on vascular contractility and focuses on the role of the endothelium, nitric oxide (NO) and K(+) channels in these responses. In wire myography studies, increasing [Ca(2+)]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine pre-contracted rabbit mesenteric arteries. [Ca(2+)]o-induced relaxations were dependent on a functional endothelium, and were inhibited by the negative allosteric CaSR modulator Calhex-231. [Ca(2+)]o-induced relaxations were reduced by inhibitors of endothelial NO synthase, guanylate cyclase, and protein kinase G. CaSR activation also induced NO production in freshly isolated endothelial cells (ECs) in experiments using the fluorescent NO indicator DAF-FM. Pre-treatment with inhibitors of large (BKCa) and intermediate (IKCa) Ca(2+)-activated K(+) channels (iberiotoxin and charybdotoxin), and Kv7 channels (linopirdine) also reduced [Ca(2+)]o-induced vasorelaxations. Increasing [Ca(2+)]o also activated IKCa currents in perforated-patch recordings of isolated mesenteric artery ECs. These findings indicate that stimulation of CaSRs induces endothelium-dependent vasorelaxations which are mediated by two separate pathways involving production of NO and activation of IKCa channels. NO stimulates PKG leading to BKCa activation in vascular smooth muscle cells, whereas IKCa activity contributes to endothelium-derived hyperpolarisations.

Inhibition of Excessive Cell Proliferation by Calcilytics in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a rare and progressive disease of unknown pathogenesis. Vascular remodeling due to excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) is a critical pathogenic event that leads to early morbidity and mortality. The excessive cell proliferation is closely linked to the augmented Ca2+ signaling in PASMCs. More recently, we have shown by an siRNA knockdown method that the Ca2+-sensing receptor (CaSR) is upregulated in PASMCs from IPAH patients, involved in the enhanced Ca2+ response and subsequent excessive cell proliferation. In this study, we examined whether pharmacological blockade of CaSR attenuated the excessive proliferation of PASMCs from IPAH patients by MTT assay. The proliferation rate of PASMCs from IPAH patients was much higher (~1.5-fold) than that of PASMCs from normal subjects and patients with chronic thromboembolic pulmonary hypertension (CTEPH). Treatment with NPS2143, an antagonist of CaSR or calcilytic, clearly suppressed the cell proliferation in a concentration-dependent manner (IC50 = 2.64 μM) in IPAH-PASMCs, but not in normal and CTEPH PASMCs. Another calcilytic, Calhex 231, which is structurally unrelated to NPS2143, also concentration-dependently inhibited the excessive proliferation of IPAH-PASMCs (IC50 = 1.89 μM). In contrast, R568, an activator of CaSR or calcimimetic, significantly facilitated the proliferation of IPAH-PASMCs (EC50 = 0.33 μM). Similar results were obtained by BrdU incorporation assay. These results reveal that the excessive PASMC proliferation was modulated by pharmacological tools of CaSR, showing us that calcilytics are useful for a novel therapeutic approach for pulmonary arterial hypertension.

Acetylcholine protects mesenteric arteries against hypoxia/reoxygenation injury via inhibiting calcium-sensing receptor

The Ca(2+)-sensing receptor (CaSR) plays an important role in regulating vascular tone. In the present study, we investigated the positive effects of the vagal neurotransmitter acetylcholine by suppressing CaSR activation in mesenteric arteries exposed to hypoxia/reoxygenation (H/R). The artery rings were exposed to a modified 'ischemia mimetic' solution and an anaerobic environment to simulate an H/R model. Our results showed that acetylcholine (10(-6) mol/L) significantly reduced the contractions induced by KCl and phenylephrine and enhanced the endothelium-dependent relaxation induced by acetylcholine. Additionally, acetylcholine reduced CaSR mRNA expression and activity when the rings were subjected to 4 h of hypoxia and 12 h of reoxygenation. Notably, the CaSR antagonist NPS2143 significantly reduced the contractions but did not improve the endothelium-dependent relaxation. When a contractile response was achieved with extracellular Ca(2+), both acetylcholine and NPS2143 reversed the H/R-induced abnormal vascular vasoconstriction, and acetylcholine reversed the calcimimetic R568-induced abnormal vascular vasoconstriction in the artery rings. In conclusion, this study suggests that acetylcholine ameliorates the dysfunctional vasoconstriction of the arteries after H/R, most likely by decreasing CaSR expression and activity, thereby inhibiting the increase in intracellular calcium concentration. Our findings may be indicative of a novel mechanism underlying ACh-induced vascular protection.

Effect of Chaiqin Chengqi Decoction on cholecystokinin receptor 1-mediated signal transduction of pancreatic acinar cells in acute necrotizing pancreatitis rats

OBJECTIVE

To investigate the effect of Chaiqin Chengqi Decoction (,CQCQD) on cholecystokinin receptor 1 (CCKR1)-mediated signal transduction of pancreatic acinar cell in rats with acute necrotic pancreatitis (ANP).

METHODS

Twenty-seven Sprague-Dawley rats were randomized into three groups: the control group, the ANP group, and the CQCQD group (9 in each group). ANP rats were induced by two intraperitoneal injections of 8% L-arginine (pH=7.0, 4.4 g/kg) over a 2-h period. Rats were treated with 1.5 mL/100 g body weight of CQCQD (CQCQD group) or physiological saline (control and ANP groups) at 2 h interval. And 6 h after induction, pancreatic tissues were collected for histopathological examination. Pancreatic acinar cells were isolated for determination of CCKR1 mRNA and protein expression, phospholipase C (PLC) and inositol-1,4,5-triphosphate (IP3), and determination of fluorescence intensity (FI) as a measure of intracellular calcium ion concentration [Ca(2+)]i.

RESULTS

The pancreatic histopathological score (6.2 ± 1.1) and the levels of PLC (1,187.2 ± 228.2 μg/mL) and IP3 (872.2 ± 88.4 μg/mL) of acinar cells in the ANP group were higher than those in the control (2.8 ± 0.4, 682.5 ± 121.8 μg/mL, 518.4 ± 115.8 μg/mL) and the CQCQD (3.8 ± 0.8, 905.3 ± 78.5 μg/mL, 611.0 ± 42.5 μg/mL) groups (P<0.05). [Ca(2+)]i FI for the ANP group (34.8±27.0) was higher than that in the control (5.1 ± 2.2) and CQCQD (12.6 ± 2.5) groups (P<0.05). The expression of pancreatic acinar cell CCKR1 mRNA in the ANP group was up-regulated (expression ratio=1.761; P=0.024) compared with the control group. The expression of pancreatic acinar cell CCKR1 mRNA in the CQCQD group was down-regulated (expression ratio=0.311; P=0.035) compared with the ANP group. The ratio of gray values of the CCKR1 and β-actin in the ANP group (1.43 ± 0.17) was higher than those in the control (0.70 ± 0.15) and CQCQD (0.79 ± 0.11) groups (P<0.05).

CONCLUSIONS

Pancreatic acinar cell calcium overload of ANP induced by L-arginine was related to the up-regulated expressions of pancreatic acinar cell CCKR1 mRNA and protein. CQCQD can down-regulate expressions of pancreatic acinar cell CCKR1 mRNA and protein to reduce the PLC and IP3 of pancreatic acinar cells, relieving the calcium overload and reducing the pathological changes in rats with ANP.

Boron-containing compounds: chemico-biological properties and expanding medicinal potential in prevention, diagnosis and therapy

INTRODUCTION

Although the medicinal use of boron-containing compounds (BCCs) had long been limited to antiseptics, in the last few decades, these compounds have been used as antibiotics or chemotherapeutic agents. In the last few years, boron has been included in the moieties of many known drugs to improve their capacity in binding to their respective target receptors.

AREAS COVERED

The current review focuses on research and patent literature of the last decade related to the development of BCCs as preventive, diagnostic and therapeutic tools. It explores the possible mechanisms of action of these compounds as well as the advantageous features of their structure and chemico-pharmacological properties.

EXPERT OPINION

Although uncertainties exist about the mechanism of action of BCCs, increasing evidence about their toxicological profile strongly suggests that many can be safely administered to humans. Even stronger evidence exists regarding the capacity of BCCs to reach multiple targets that are involved in the treatment of common diseases. It seems fair to say that some BCCs will reach the market for medicinal use in the near future, not only for targeting microbial or neoplastic systems but also for acting on cell-signaling processes involved in many other disorders.

Ca2+-sensing receptor cleavage by calpain partially accounts for altered vascular reactivity in mice fed a high-fat diet

The Ca-sensing receptor (CaSR) is expressed in endothelial and smooth muscle cells, but its role in regulating vascular reactivity is unclear, as are the effects of disease on CaSR function and expression. We studied vascular reactivity in aortic segments from healthy and diabetic mice, combined with in vitro proteolysis studies and Western blot analyses of CaSR expression in tissue samples. In endothelium-intact aortic rings, extracellular Ca elicited a nitric oxide-dependent relaxation that was attenuated by the CaSR antagonist, NPS2390. The calcimimetic, calindol, induced the endothelium-independent relaxation of aortic segments that was also sensitive to NPS2390. The antagonist failed to affect responses to acetylcholine or U46619 but attenuated contractions to phenylephrine and potassium. In mice fed a Western-type diet, phenylephrine-induced contractions and calindol-induced relaxations were markedly attenuated, and CaSR expression was decreased. The latter phenomenon could be attributed to the activation of the Ca-dependent protease, µ-calpain, and the subsequent proteolytic cleavage of the CaSR. CaSR activation in smooth muscle cells modulates vascular responsiveness to Ca-elevating agonists. These effects are blunted during metabolic stress because of the limited proteolysis of the CaSR by calpain. The loss of the CaSR function may predispose to the macrovascular late complications associated with diabetes.

Regulation of ca(2+) signaling in pulmonary hypertension

Understanding the cellular and molecular mechanisms involved in the development and progression of pulmonary hypertension (PH) remains imperative if we are to successfully improve the quality of life and life span of patients with the disease. A whole plethora of mechanisms are associated with the development and progression of PH. Such complexity makes it difficult to isolate one particular pathway to target clinically. Changes in intracellular free calcium concentration, the most common intracellular second messenger, can have significant impact in defining the pathogenic mechanisms leading to its development and persistence. Signaling pathways leading to the elevation of [Ca(2+)](cyt) contribute to pulmonary vasoconstriction, excessive proliferation of smooth muscle cells and ultimately pulmonary vascular remodeling. This current review serves to summarize the some of the most recent advances in the regulation of calcium during pulmonary hypertension.

Dihydropyridine Ca(2+) channel blockers increase cytosolic [Ca(2+)] by activating Ca(2+)-sensing receptors in pulmonary arterial smooth muscle cells

RATIONALE

An increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC proliferation and pulmonary vascular remodeling. The dihydropyridine Ca(2+) channel blockers, such as nifedipine, have been used for treatment of idiopathic pulmonary arterial hypertension (IPAH).

OBJECTIVE

Our previous study demonstrated that the Ca(2+)-sensing receptor (CaSR) was upregulated and the extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) was enhanced in PASMC from patients with IPAH and animals with experimental pulmonary hypertension. Here, we report that the dihydropyridines (eg, nifedipine) increase [Ca(2+)](cyt) by activating CaSR in PASMC from IPAH patients (in which CaSR is upregulated), but not in normal PASMC.

METHODS AND RESULTS

The nifedipine-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC was concentration dependent with a half maximal effective concentration of 0.20 µmol/L. Knockdown of CaSR with siRNA in IPAH-PASMC significantly inhibited the nifedipine-induced increase in [Ca(2+)](cyt), whereas overexpression of CaSR in normal PASMC conferred the nifedipine-induced rise in [Ca(2+)](cyt). Other dihydropyridines, nicardipine and Bay K8644, had similar augmenting effects on the CaSR-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC; however, the nondihydropyridine blockers, such as diltiazem and verapamil, had no effect on the CaSR-mediated rise in [Ca(2+)](cyt).

CONCLUSIONS

The dihydropyridine derivatives increase [Ca(2+)](cyt) by potentiating the activity of CaSR in PASMC independently of their blocking (or activating) effect on Ca(2+) channels; therefore, it is possible that the use of dihydropyridine Ca(2+) channel blockers (eg, nifedipine) to treat IPAH patients with upregulated CaSR in PASMC may exacerbate pulmonary hypertension.

The effects of extracellular calcium-sensing receptor ligands on the contractility of pregnant human myometrium in vitro

Ligands for extracellular calcium-sensing (CaS) receptors inhibit oxytocin-induced contractions of the rat's uterus. In this study, we investigated whether the CaS receptor ligands calindol, cinacalcet, and calhex 231 have similar effects on pregnant human myometrium. We compared their effects to those of the calcium-channel blocker nifedipine. In conventional concentration-effect experiments, both the mean contractile force (MCF) and the maximum amplitude of contractions induced by 1 nmol/L oxytocin were inhibited by nifedipine. Calindol and cinacalcet were ineffective as inhibitors, while calhex-231 produced partial inhibition. When single 10 μmol/L doses were applied calhex-231 produced a slowly developing inhibition, reducing the MCF to 38%, and amplitude to 34%, of vehicle controls after 1 hour. In similar experiments, calindol was ineffective while cinacalcet weakly inhibited only the amplitude. Immunohistochemistry revealed sparse expression of CaS receptors in pregnant human myometrium.

Extracellular calcium-sensing receptor is critical in hypoxic pulmonary vasoconstriction

AIMS

The initiation of hypoxic pulmonary vasoconstriction (HPV) involves an increase in cytosolic calcium ([Ca(2+)](i)) in pulmonary artery (PA) smooth muscle cells (PASMCs). Both the processes depend on extracellular Ca(2+). Extracellular Ca(2+) can be sensed by extracellular calcium-sensing receptor (CaSR). This study aims at determining whether CaSR is pivotal in the initiation of HPV.

RESULTS

Experiments were performed in cultured PASMCs, isolated PAs, and rats including CaSR knockdown preparations. Both hypoxia and H(2)O(2) equivalent to the level achieved by hypoxia increased [Ca(2+)](i) in an extracellular Ca(2+)-dependent manner in PASMCs, and this was inhibited by CaSR knockdown or its negative allosteric modulator, Calhex231. Hypoxia-increased H(2)O(2) generation was diminished by mitochondria depletion. Mitochondria depletion abolished hypoxia-induced [Ca(2+)](i) increase (HICI), which was reversed by H(2)O(2) repletion. CaSR knockdown or Calhex231, however, prevented the reversible effect of H(2)O(2). HICI was abolished by catalase-polyethylene glycol (PEG-Catalase), not superoxide dismutase-polyethylene glycol (PEG-SOD) pretreatment, attenuated by ryanodine receptor3-knockdown or inhibition of store-operated Ca(2+) entry. HPV in vitro and in vivo was inhibited by Calhex231 and by CaSR knockdown.

INNOVATION

A novel mechanism underlying HPV is revealed by the role of CaSR in orchestrating reactive oxygen species and [Ca(2+)](i) signaling.

CONCLUSIONS

The activation of mitochondrial H(2)O(2)-sensitized CaSR by extracellular Ca(2+) mediates HICI in PASMCs and, thus, initiates HPV.

Enhanced Ca(2+)-sensing receptor function in idiopathic pulmonary arterial hypertension

RATIONALE

A rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. Increased resting [Ca(2+)](cyt) and enhanced Ca(2+) influx have been implicated in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH).

OBJECTIVE

We examined whether the extracellular Ca(2+)-sensing receptor (CaSR) is involved in the enhanced Ca(2+) influx and proliferation in IPAH-PASMC and whether blockade of CaSR inhibits experimental pulmonary hypertension.

METHODS AND RESULTS

In normal PASMC superfused with Ca(2+)-free solution, addition of 2.2 mmol/L Ca(2+) to the perfusate had little effect on [Ca(2+)](cyt). In IPAH-PASMC, however, restoration of extracellular Ca(2+) induced a significant increase in [Ca(2+)](cyt). Extracellular application of spermine also markedly raised [Ca(2+)](cyt) in IPAH-PASMC but not in normal PASMC. The calcimimetic R568 enhanced, whereas the calcilytic NPS 2143 attenuated, the extracellular Ca(2+)-induced [Ca(2+)](cyt) rise in IPAH-PASMC. Furthermore, the protein expression level of CaSR in IPAH-PASMC was greater than in normal PASMC; knockdown of CaSR in IPAH-PASMC with siRNA attenuated the extracellular Ca(2+)-mediated [Ca(2+)](cyt) increase and inhibited IPAH-PASMC proliferation. Using animal models of pulmonary hypertension, our data showed that CaSR expression and function were both enhanced in PASMC, whereas intraperitoneal injection of the calcilytic NPS 2143 prevented the development of pulmonary hypertension and right ventricular hypertrophy in rats injected with monocrotaline and mice exposed to hypoxia.

CONCLUSIONS

The extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) due to upregulated CaSR is a novel pathogenic mechanism contributing to the augmented Ca(2+) influx and excessive PASMC proliferation in patients and animals with pulmonary arterial hypertension.