Store-operated Ca2+ entry is exaggerated in fresh preglomerular vascular smooth muscle cells of SHR

7-Hydroxycoumarin Induces Vasorelaxation in Animals with Essential Hypertension: Focus on Potassium Channels and Intracellular Ca2+ Mobilization

Cardiovascular diseases (CVD) are the deadliest noncommunicable disease worldwide. Hypertension is the most prevalent risk factor for the development of CVD. Although there is a wide range of antihypertensive drugs, there still remains a lack of blood pressure control options for hypertensive patients. Additionally, natural products remain crucial to the design of new drugs. The natural product 7-hydroxycoumarin (7-HC) exhibits pharmacological properties linked to antihypertensive mechanisms of action. This study aimed to evaluate the vascular effects of 7-HC in an experimental model of essential hypertension. The isometric tension measurements assessed the relaxant effect induced by 7-HC (0.001 μM–300 μM) in superior mesenteric arteries isolated from hypertensive rats (SHR, 200–300 g). Our results suggest that the relaxant effect induced by 7-HC rely on K⁺-channels (K_ATP, BK_Ca, and, to a lesser extent, K_v) activation and also on Ca²⁺ influx from sarcolemma and sarcoplasmic reticulum mobilization (inositol 1,4,5-triphosphate (IP3) and ryanodine receptors). Moreover, 7-HC diminishes the mesenteric artery’s responsiveness to α1-adrenergic agonist challenge and improves the actions of the muscarinic agonist and NO donor. The present work demonstrated that the relaxant mechanism of 7-HC in SHR involves endothelium-independent vasorelaxant factors. Additionally, 7-HC reduced vasoconstriction of the sympathetic agonist while improving vascular endothelium-dependent and independent relaxation.

Store-operated calcium entry: Pivotal roles in renal physiology and pathophysiology

Research conducted over the last two decades has dramatically advanced the understanding of store-operated calcium channels (SOCC) and their impact on renal function. Kidneys contain many types of cells, including those specialized for glomerular filtration (fenestrated capillary endothelium, podocytes), water and solute transport (tubular epithelium), and regulation of glomerular filtration and renal blood flow (vascular smooth muscle cells, mesangial cells). The highly integrated function of these myriad cells effects renal control of blood pressure, extracellular fluid volume and osmolality, electrolyte balance, and acid-base homeostasis. Many of these cells are regulated by Ca²⁺ signaling. Recent evidence demonstrates that SOCCs are major Ca²⁺ entry portals in several renal cell types. SOCC is activated by depletion of Ca²⁺ stores in the sarco/endoplasmic reticulum, which communicates with plasma membrane SOCC via the Ca²⁺ sensor Stromal Interaction Molecule 1 (STIM1). Orai1 is recognized as the main pore-forming subunit of SOCC in the plasma membrane. Orai proteins alone can form highly Ca²⁺ selective SOCC channels. Also, members of the Transient Receptor Potential Canonical (TRPC) channel family are proposed to form heteromeric complexes with Orai1 subunits, forming SOCC with low Ca²⁺ selectivity. Recently, Ca²⁺ entry through SOCC, known as store-operated Ca²⁺ entry (SOCE), was identified in glomerular mesangial cells, tubular epithelium, and renovascular smooth muscle cells. The physiological and pathological relevance and the characterization of SOCC complexes in those cells are still unclear. In this review, we summarize the current knowledge of SOCC and their roles in renal glomerular, tubular and vascular cells, including studies from our laboratory, emphasizing SOCE regulation of fibrotic protein deposition. Understanding the diverse roles of SOCE in different renal cell types is essential, as SOCC and its signaling pathways are emerging targets for treatment of SOCE-related diseases.

Anti-hypertensive and vasodilatory effects of amended Banxia Baizhu Tianma Tang

Although Banxia Baizhu Tianma Tang (BBT) has been long administered for hypertensive treatment in Traditional Chinese Medicine (TCM), the ratio of the herbal components that makes up the formulation has not been optimized with respect to the anti-hypertensive effect that it inherently possesses. A newly amended BBT (ABBT) formulation was developed using the evidence-based approach of orthogonal stimulus-response compatibility model. The ABBT showed enhanced therapeutic effect while maintaining its traditional theoretical approach rooted in TCM. This study was designed to investigate the possible mechanism of actions involved in the vasodilatory activity of ABBT-50 by evaluating its vasodilative effect on isolated Sprague Dawley rats in the presence of absence of various antagonists. When pre-contracted with phenylephrine, relaxation was observed in endothelium intact (EC₅₀=0.027±0.003mg/ml, R_max=109.8±2.12%) and denuded aortic rings (EC₅₀=0.409±0.073mg/ml, R_max=63.15±1.78%), as well as in endothelium intact aortic rings pre-contracted with potassium chloride (EC₅₀=32.7±12.16mg/ml, R_max=34.02±3.82%). Significant decrease in the vasodilative effect of ABBT-50 was observed in the presence of Nω-nitro-l-arginine methyl ester (EC₅₀=0.12±0.021mg/ml, R_max=75.33±3.28%), 1H-[1,2,4] Oxadiazolo[4,3-a]quinoxalin-1-one (EC₅₀=0.463±0.18mg/ml, R_max=54.48±2.02%), methylene blue (EC₅₀=0.19±0.037mg/ml, R_max=83.69±3.19%), indomethacin (EC₅₀=0.313±0.046mg/ml, R_max=71.33±4.12%), atropine (EC₅₀=0.146±0.013mg/ml, R_max=77.2±3.41%), and 4-aminopyridine (EC₅₀=0.045±0.008mg/ml, R_max=95.55±2.36%). ABBT-50 was also suppressing Ca²⁺ release from sarcoplasmic reticulum and inhibiting calcium channels. Vasodilatory effects of ABBT-50 are mediated through NO/sGC/cGMP cascade and PGI₂, followed by muscarinic pathways and calcium channels.

Store-Operated Ca2+ Channel in Renal Microcirculation and Glomeruli

Store-operated Ca2+ channel (SOC) is defined as a channel that opens in response to depletion of the internal Ca2+ stores. During the last decade, many investigators have made a great effort to identify and characterize SOC, and to evaluate its physiologic function and pathophysiologic relevance in a variety of cell lines, primary cultures, and native tissues. To date, accumulating evidence has demonstrated that SOC is an essential Ca2+ entry mechanism in vascular smooth-muscle cells of renal microvasculature and glomerular mesangial cells, both of which tightly control glomerular hemodynamics and filtration. Store-operated Ca2+, combined with other types of Ca2+ entry channels, constitutes a profile of Ca2+ changes in response to physiologic vasoconstrictors and, thereby, regulates renal microcirculation and mesangial function. In addition, SOC is associated with altered Ca2+ signaling occurring in diseased kidneys, such as diabetic nephropathy. Although the gating mechanism and molecular identity of SOC are still enigmatic and may be cell-type and tissue specific, data from several independent groups suggest that protein kinase C plays an important role in SOC activation and that certain isoforms of canonical transient receptor potential (TRPC) proteins are candidates of SOC in renal mlcrovessels and mesangial cells.

Excitation-Contraction Coupling and Excitation-Transcription Coupling in Blood Vessels: Their Possible Interactions in Hypertensive Vascular Remodeling

Vascular smooth muscle cells (VSMC) display considerable phenotype plasticity which can be studied in vivo on vascular remodeling which occurs during acute or chronic vascular injury. In differentiated cells, which represent contractile phenotype, there are characteristic rapid transient changes of intracellular Ca2+ concentration ([Ca2+]i), while the resting cytosolic [Ca2+]i concentration is low. It is mainly caused by two components of the Ca2+ signaling pathways: Ca2+ entry via L-type voltage-dependent Ca2+ channels and dynamic involvement of intracellular stores. Proliferative VSMC phenotype is characterized by long-lasting [Ca2+]i oscillations accompanied by sustained elevation of basal [Ca2+]i. During the switch from contractile to proliferative phenotype there is a general transition from voltage-dependent Ca2+ entry to voltage-independent Ca2+ entry into the cell. These changes are due to the altered gene expression which is dependent on specific transcription factors activated by various stimuli. It is an open question whether abnormal VSMC phenotype reported in rats with genetic hypertension (such as spontaneously hypertensive rats) might be partially caused by a shift from contractile to proliferative VSMC phenotype.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

Superoxide enhances Ca2+ entry through L-type channels in the renal afferent arteriole

Reactive oxygen species regulate cardiovascular and renal function in health and disease. Superoxide participates in acute calcium signaling in afferent arterioles and renal vasoconstriction produced by angiotensin II, endothelin, thromboxane, and pressure-induced myogenic tone. Known mechanisms by which superoxide acts include quenching of nitric oxide and increased ADP ribosyl cyclase/ryanodine-mediated calcium mobilization. The effect(s) of superoxide on other calcium signaling pathways in the renal microcirculation is poorly understood. The present experiments examined the acute effect of superoxide generated by paraquat on calcium entry pathways in isolated rat afferent arterioles. The peak increase in cytosolic calcium concentration caused by KCl (40 mmol/L) was 99±14 nmol/L. The response to this membrane depolarization was mediated exclusively by L-type channels because it was abolished by nifedipine but was unaffected by the T-type channel blocker mibefradil. Paraquat increased superoxide production (dihydroethidium fluorescence), tripled the peak response to KCl to 314±68 nmol/L (P<0.001) and doubled the plateau response. These effects were abolished by tempol and nitroblue tetrazolium, but not by catalase, confirming actions of superoxide and not of hydrogen peroxide. Unaffected by paraquat and superoxide was calcium entry through store-operated calcium channels activated by thapsigargin-induced calcium depletion of sarcoplasmic reticular stores. Also unresponsive to paraquat was ryanodine receptor-mediated calcium-induced calcium release from the sarcoplasmic reticulum. Our results provide new evidence that superoxide enhances calcium entry through L-type channels activated by membrane depolarization in rat cortical afferent arterioles, without affecting calcium entry through store-operated entry or ryanodine receptor-mediated calcium mobilization.

Impaired P2X signalling pathways in renal microvascular myocytes in genetic hypertension

AIMS

P2X receptors (P2XRs) mediate sympathetic control and autoregulation of renal circulation triggering preglomerular vasoconstriction, which protects glomeruli from elevated pressures. Although previous studies established a casual link between glomerular susceptibility to hypertensive injury and decreased preglomerular vascular reactivity to P2XR activation, the mechanisms of attenuation of the P2XR signalling in hypertension remained unknown. We aimed to analyse molecular mechanisms of the impairment of P2XR signalling in renal vascular smooth muscle cells (RVSMCs) in genetic hypertension.

METHODS AND RESULTS

We compared the expression of pertinent genes and P2XR-linked Ca(2+) entry and Ca(2+) release mechanisms in RVSMCs of spontaneously hypertensive rats (SHRs) and their normotensive controls, Wistar Kyoto (WKY) rats. We found that, in SHR RVSMCs, P2XR-linked Ca(2+) entry and Ca(2+) release from the sarcoplasmic reticulum (SR) are both significantly reduced. The former is due to down-regulation of the P2X1 subunit. The latter is caused by a decrease of the SR Ca(2+) load. The SR Ca(2+) load reduction is caused by attenuated Ca(2+) uptake via down-regulated sarco-/endoplasmic reticulum Ca(2+)-ATPase 2b and elevated Ca(2+) leak from the SR via ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors. Spontaneous activity of these Ca(2+)-release channels is augmented due to up-regulation of RyR type 2 and elevated IP3 production by up-regulated phospholipase C-β1.

CONCLUSIONS

Our study unravels the cellular and molecular mechanisms of attenuation of P2XR-mediated preglomerular vasoconstriction that elevates glomerular susceptibility to harmful hypertensive pressures. This provides an important impetus towards understanding of the pathology of hypertensive renal injury.

High glucose and diabetes enhanced store-operated Ca(2+) entry and increased expression of its signaling proteins in mesangial cells

The present study was conducted to determine whether and how store-operated Ca(2+) entry (SOCE) in glomerular mesangial cells (MCs) was altered by high glucose (HG) and diabetes. Human MCs were treated with either normal glucose or HG for different time periods. Cyclopiazonic acid-induced SOCE was significantly greater in the MCs with 7-day HG treatment and the response was completely abolished by GSK-7975A, a selective inhibitor of store-operated Ca(2+) channels. Similarly, the inositol 1,4,5-trisphosphate-induced store-operated Ca(2+) currents were significantly enhanced in the MCs treated with HG for 7 days, and the enhanced response was abolished by both GSK-7975A and La(3+). In contrast, receptor-operated Ca(2+) entry in MCs was significantly reduced by HG treatment. Western blotting showed that HG increased the expression levels of STIM1 and Orai1 in cultured MCs. A significant HG effect occurred at a concentration as low as 10 mM, but required a minimum of 7 days. The HG effect in cultured MCs was recapitulated in renal glomeruli/cortex of both type I and II diabetic rats. Furthermore, quantitative real-time RT-PCR revealed that a 6-day HG treatment significantly increased the mRNA expression level of STIM1. However, the expressions of STIM2 and Orai1 transcripts were not affected by HG. Taken together, these results suggest that HG/diabetes enhanced SOCE in MCs by increasing STIM1/Orai1 protein expressions. HG upregulates STIM1 by promoting its transcription but increases Orai1 protein through a posttranscriptional mechanism.

Overview of animal models of attention deficit hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous, highly heritable, behavioral disorder that affects ∼5% to 10% of children worldwide. Although animal models cannot truly reflect human psychiatric disorders, they can provide insight into the disorder that cannot be obtained from human studies because of the limitations of available techniques. Genetic models include the spontaneously hypertensive rat (SHR), the Naples High Excitability (NHE) rat, poor performers in the 5-choice serial reaction time (5-CSRT) task, the dopamine transporter (DAT) knock-out mouse, the SNAP-25 deficient mutant coloboma mouse, mice expressing a human mutant thyroid hormone receptor, a nicotinic receptor knock-out mouse, and a tachykinin-1 (NK1) receptor knock-out mouse. Chemically induced models of ADHD include prenatal or early postnatal exposure to ethanol, nicotine, polychlorinated biphenyls, or 6-hydroxydopamine (6-OHDA). Environmentally induced models have also been suggested; these include neonatal anoxia and rat pups reared in social isolation. The major insight provided by animal models was the consistency of findings regarding the involvement of dopaminergic, noradrenergic, and sometimes also serotonergic systems, as well as more fundamental defects in neurotransmission.

S1P activates store-operated calcium entry via receptor- and non-receptor-mediated pathways in vascular smooth muscle cells

Sphingosine-1-phosphate (S1P) has been shown to modulate intracellular Ca(2+) through both G protein-coupled receptors and intracellular second messenger pathways. The precise mechanism by which S1P activates store-operated calcium entry (SOCE) in vascular smooth muscle cells (VSMCs) has not been fully characterized. Because sphingolipids and Ca(2+) modulate proliferation and constriction in VSMCs, characterizing the connection between S1P and SOCE may provide novel therapeutic targets for vascular diseases. We found that S1P triggered STIM1 puncta formation and SOCE in VSMCs. S1P-activated SOCE was inhibited by 2-aminoethoxydiphenyl borate (2-APB), diethylstilbestrol (DES), and gadolinium (Gd(3+)). SOCE was observed in VSMCs lacking either S1P(2) or S1P(3) receptors, suggesting that S1P acts via multiple signaling pathways. Indeed, both extracellular and intracellular S1P application increased the total internal reflection fluorescence signal in VSMCs cells transfected with STIM1-yellow fluorescent protein in a 2-APB-sensitive manner. These data, and the fact that 2-APB, DES, and Gd(3+) all inhibited S1P-induced cerebral artery constriction, suggest that SOCE modulates S1P-induced vasoconstriction in vivo. Finally, S1P-induced SOCE was larger in proliferative than in contractile VSMCs, correlating with increases in STIM1, Orai1, S1P(1), and S1P(3) receptor mRNA. These data demonstrate that S1P can act through both receptors and a novel intracellular pathway to activate SOCE. Because S1P-induced SOCE contributes to vessel constriction and is increased in proliferative VSMCs, it is likely that S1P/SOCE signaling in proliferative VSMCs may play a role in vascular dysfunction such as atherosclerosis and diabetes.

Increased rhythmicity in hypertensive arterial smooth muscle is linked to transient receptor potential canonical channels

Vasomotion describes oscillations of arterial vascular tone due to synchronized changes of intracellular calcium concentrations. Since increased calcium influx into vascular smooth muscle cells from spontaneously hypertensive rats (SHR) has been associated with variances of transient receptor potential canonical (TRPC) channels, in the present study we tested the hypothesis that increased vasomotion in hypertension is directly linked to increased TRPC expression. Using a small vessel myograph we observed significantly increased norepinephrine-induced vasomotion in mesenteric arterioles from SHR compared to normotensive Wistar–Kyoto (WKY) rats. Using immunoblottings we obtained significantly increased expression of TRPC1, TRPC3 and TRPC5 in mesenteric arterioles from SHR compared to WKY, whereas TRPC4 and TRPC6 showed no differences. Norepinephrine-induced vasomotion from SHR was significantly reduced in the presence of verapamil, SKF96365, 2-aminoethoxydiphenylborane (2-APB) or gadolinium. Pre-incubation of mesenteric arterioles with anti-TRPC1 and anti-TRPC3 antibodies significantly reduced norepinephrine-induced vasomotion and calcium influx. Control experiments with pre-incubation of TRPC antibodies plus their respective antigenic peptide or in the presence of anti-β-actin antibodies or random immunoglobulins not related to TRPC channels showed no inhibitory effects of norepinephrine-induced vasomotion and calcium influx. Administration of candesartan or telmisartan, but not amlodipine to SHR for 16 weeks significantly reduced either the expression of TRPC1, TRPC3 and TRPC5 as well as norepinephrine-induced vasomotion in mesenteric arterioles. In conclusion we gave experimental evidence that the increased TRPC1, TRPC3 and TRPC5 expression in mesenteric arterioles from SHR causes increased vasomotion in hypertension.

STIM proteins: integrators of signalling pathways in development, differentiation and disease

The stromal interaction molecules STIM1 and STIM2 are endoplasmic reticulum Ca²⁺ sensors, serving to detect changes in receptor-mediated ER Ca²⁺ store depletion and to relay this information to plasma membrane localized proteins, including the store-operated Ca²⁺ channels of the ORAI family. The resulting Ca²⁺ influx sustains the high cytosolic Ca²⁺ levels required for activation of many intracellular signal transducers such as the NFAT family of transcription factors. Models of STIM protein deficiency in mice, Drosophila melanogaster and Caenorhabditis elegans, in addition to the phenotype of patients bearing mutations in STIM1 have provided great insight into the role of these proteins in cell physiology and pathology. It is now becoming clear that STIM1 and STIM2 are critical for the development and functioning of many cell types, including lymphocytes, skeletal and smooth muscle myoblasts, adipocytes and neurons, and can interact with a variety of signalling proteins and pathways in a cell- and tissue-type specific manner. This review focuses on the role of STIM proteins in development, differentiation and disease, in particular highlighting the functional differences between STIM1 and STIM2.

NAADP receptors mediate calcium signaling stimulated by endothelin-1 and norepinephrine in renal afferent arterioles

The enzyme ADP-ribosyl (ADPR) cyclase plays a significant role in mediating increases in renal afferent arteriolar cytosolic calcium concentration ([Ca(2+)](i)) in vitro and renal vasoconstriction in vivo. ADPR cyclase produces cyclic ADP ribose, a second messenger that contributes importantly to ryanodine receptor-mediated Ca(2+) mobilization in renal vascular responses to several vasoconstrictors. Recent studies in nonrenal vascular smooth muscle cells (VSMC) have shown that nicotinic acid adenine dinucleotide phosphate (NAADP), another second messenger generated by ADPR cyclase, may contribute to Ca(2+) signaling. We tested the hypothesis that a Ca(2+) signaling pathway involving NAADP receptors participates in afferent arteriolar [Ca(2+)](i) responses to the G protein-coupled receptor agonists endothelin-1 (ET-1) and norepinephrine (NE). To test this, we isolated rat renal afferent arterioles and measured [Ca(2+)](I) using fura-2 fluorescence. We compared peak [Ca(2+)](i) increases stimulated by ET-1 and NE in the presence and absence of inhibitors of acidic organelle-dependent Ca(2+) signaling and NAADP receptors. Vacuolar H(+)-ATPase inhibitors bafilomycin A1 and concanamycin A, disruptors of pH and Ca(2+) stores of lysosomes and other acidic organelles, individually antagonized [Ca(2+)](i) responses to ET-1 and NE by 40-50% (P < 0.05). The recently discovered NAADP receptor inhibitor Ned-19 attenuated [Ca(2+)](i) responses to ET-1 or NE by 60-70% (P < 0.05). We conclude that NAADP receptors contribute to both ET-1- and NE-induced [Ca(2+)](i) responses in afferent arterioles, an effect likely dependent on acidic vesicle, possibly involving lysosome, signaling in VSMC in the renal microcirculation.

Cellular mediators of renal vascular dysfunction in hypertension

The renal vasculature plays a major role in the regulation of renal blood flow and the ability of the kidney to control the plasma volume and blood pressure. Renal vascular dysfunction is associated with renal vasoconstriction, decreased renal blood flow, and consequent increase in plasma volume and has been demonstrated in several forms of hypertension (HTN), including genetic and salt-sensitive HTN. Several predisposing factors and cellular mediators have been implicated, but the relationship between their actions on the renal vasculature and the consequent effects on renal tubular function in the setting of HTN is not clearly defined. Gene mutations/defects in an ion channel, a membrane ion transporter, and/or a regulatory enzyme in the nephron and renal vasculature may be a primary cause of renal vascular dysfunction. Environmental risk factors, such as high dietary salt intake, vascular inflammation, and oxidative stress further promote renal vascular dysfunction. Renal endothelial cell dysfunction is manifested as a decrease in the release of vasodilatory mediators, such as nitric oxide, prostacyclin, and hyperpolarizing factors, and/or an increase in vasoconstrictive mediators, such as endothelin, angiotensin II, and thromboxane A(2). Also, an increase in the amount/activity of intracellular Ca(2+) concentration, protein kinase C, Rho kinase, and mitogen-activated protein kinase in vascular smooth muscle promotes renal vasoconstriction. Matrix metalloproteinases and their inhibitors could also modify the composition of the extracellular matrix and lead to renal vascular remodeling. Synergistic interactions between the genetic and environmental risk factors on the cellular mediators of renal vascular dysfunction cause persistent renal vasoconstriction, increased renal vascular resistance, and decreased renal blood flow, and, consequently, lead to a disturbance in the renal control mechanisms of water and electrolyte balance, increased plasma volume, and HTN. Targeting the underlying genetic defects, environmental risk factors, and the aberrant renal vascular mediators involved should provide complementary strategies in the management of HTN.

Increased activation of stromal interaction molecule-1/Orai-1 in aorta from hypertensive rats: a novel insight into vascular dysfunction

Disturbances in the regulation of cytosolic calcium (Ca(2+)) concentration play a key role in the vascular dysfunction associated with arterial hypertension. Stromal interaction molecules (STIMs) and Orai proteins represent a novel mechanism to control store-operated Ca(2+) entry. Although STIMs act as Ca(2+) sensors for the intracellular Ca(2+) stores, Orai is the putative pore-forming component of Ca(2+) release-activated Ca(2+) channels at the plasma membrane. We hypothesized that augmented activation of Ca(2+) release-activated Ca(2+)/Orai-1, through enhanced activity of STIM-1, plays a role in increased basal tonus and vascular reactivity in hypertensive animals. Endothelium-denuded aortic rings from Wistar-Kyoto and stroke-prone spontaneously hypertensive rats were used to evaluate contractions because of Ca(2+) influx. Depletion of intracellular Ca(2+) stores, which induces Ca(2+) release-activated Ca(2+) activation, was performed by placing arteries in Ca(2+) free-EGTA buffer. The addition of the Ca(2+) regular buffer produced greater contractions in aortas from stroke-prone spontaneously hypertensive rats versus Wistar-Kyoto rats. Thapsigargin (10 micromol/L), an inhibitor of the sarcoplasmic reticulum Ca(2+) ATPase, further increased these contractions, especially in stroke-prone spontaneously hypertensive rat aorta. Addition of the Ca(2+) release-activated Ca(2+) channel inhibitors 2-aminoethoxydiphenyl borate (100 micromol/L) or gadolinium (100 micromol/L), as well as neutralizing antibodies to STIM-1 or Orai-1, abolished thapsigargin-increased contraction and the differences in spontaneous tone between the groups. Expression of Orai-1 and STIM-1 proteins was increased in aorta from stroke-prone spontaneously hypertensive rats when compared with Wistar-Kyoto rats. These results support the hypothesis that both Orai-1 and STIM-1 contribute to abnormal vascular function in hypertension. Augmented activation of STIM-1/Orai-1 may represent the mechanism that leads to impaired control of intracellular Ca(2+) levels in hypertension.

An essential role for stromal interaction molecule 1 in neointima formation following arterial injury

AIMS

There is evidence to suggest that stromal interaction molecule 1 (STIM1) functions as a Ca2+ sensor on the endoplasmic reticulum, leading to transduction of signals to the plasma membrane and opening of store-operated Ca2+ channels (SOC). SOC have been detected in vascular smooth muscle cells (VSMCs) and are thought to have an essential role in the regulation of contraction and cell proliferation. We hypothesized that knockdown of STIM1 inhibits VSMC proliferation and suppresses neointimal hyperplasia.

METHODS AND RESULTS

We examined the effect of the knockdown of STIM1 using a rat balloon injury model and cultured rat aortic VSMCs. Interestingly, knockdown of rat STIM1 by adenovirus delivery of small interfering RNA (siRNA) significantly suppressed neointimal hyperplasia in a rat carotid artery balloon injury model at 14 days after injury. The re-expression of human STIM1 to smooth muscle reversed the effect of STIM1 knockdown on neointimal formation. Rat aortic VSMCs were used for the in vitro assays. Knockdown of endogenous STIM1 significantly inhibited proliferation and migration of VSMCs. Moreover, STIM1 knockdown induced cell-cycle arrest in G0/G1 and resulted in a marked decrease in SOC. Replenishment with recombinant human STIM1 reversed the effect of siRNA knockdown. These results suggest STIM1 has a critical role in neointimal formation in a rat model of vascular injury.

CONCLUSION

STIM1 may represent a novel therapeutic target in the prevention of restenosis after vascular interventions.

Neurobiology of animal models of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a heterogeneous, highly heritable, disorder resulting from complex gene-gene and gene-environment interactions. The defining symptoms of hyperactivity, impulsivity and impaired sustained attention are not unique to ADHD. It is therefore not surprising that animals with distinctly different neural defects model the behavioural characteristics of the disorder. Consistent with ADHD being a developmental disorder, animal models are either genetic (spontaneously hypertensive rats (SHR), dopamine transporter (DAT) knock-out mice, SNAP-25 mutant mice, mice expressing a mutant thyroid receptor) or have suffered an insult to the central nervous system during the early stages of development (anoxia, 6-hydroxydopamine). It appears that neural transmission is impaired by either direct disruption of dopaminergic transmission or a more general impairment of neurotransmission that gives rise to compensatory changes in monoaminergic systems that are not sufficient to completely normalize neural function. In general, results obtained with animal studies suggest that dopamine neurons are functionally impaired. However, evidence obtained from some animal models suggests that the noradrenergic and serotonergic neurotransmitter systems may be the target of drugs that ameliorate ADHD symptoms.

Voltage-gated Ca2+ entry and ryanodine receptor Ca2+-induced Ca2+ release in preglomerular arterioles

We have previously shown that in afferent arterioles, angiotensin II (ANG II) involves activation of the inositol trisphosphate receptor (IP(3)R), activation of adenine diphosphoribose (ADPR) cyclase, and amplification of the initial IP(3)R-stimulated release of cytosolic Ca(2+) ([Ca(2+)](i)) from the sarcoplasmic reticulum (SR) (Fellner SK, Arendshorst WJ. Am J Physiol Renal Physiol 288: F785-F791, 2004). The response of the ryanodine receptor (RyR) to local increases in [Ca(2+)](i) is defined as calcium-induced calcium release (CICR). To investigate whether Ca(2+) entry via voltage-gated channels (VGCC) can stimulate CICR, we treated fura 2-loaded, freshly isolated afferent arterioles with KCl (40 mM; high KCl). In control arterioles, peak [Ca(2+)](i) increased by 165 +/- 10 nM. Locking the RyR in the closed position with ryanodine (100 microM) inhibited the [Ca(2+)](i) response by 59% (P < 0.01). 8-Br cADPR, a specific blocker of the ability of cyclic ADPR (cADPR) to sensitize the RyR to Ca(2+), caused a 43% inhibition. We suggest that the lower inhibition by 8-Br cADPR (P = 0.02, ryanodine vs. 8-Br cADPR) represents endogenously active ADPR cyclase. Depletion of SR Ca(2+) stores by inhibiting the SR Ca(2+)-ATPase with cyclopiazonic acid or thapsigargin blocked the [Ca(2+)](i) responses to KCl by 51% (P not significant vs. ryanodine or 8-Br cADPR). These data suggest that about half of the increase in [Ca(2+)](i) induced by high KCl is accomplished by activation of CICR through the ability of entered Ca(2+) to expose the RyR to high local concentrations of Ca(2+) and that endogenous cADPR contributes to the process.

Contribution of both Ca2+ entry and Ca2+ sensitization to the alpha1-adrenergic vasoconstriction of rat penile small arteries

Sympathetic adrenergic nerves maintain the flaccid state of the penis through the tonic release of norepinephrine that contracts trabecular and arterial smooth muscle. Simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)) and tension and experiments with alpha-toxin-permeabilized arteries were performed in branches of the rat dorsal penile artery to investigate the intracellular Ca(2+) signaling pathways underlying alpha(1)-adrenergic vasoconstriction. Phenylephrine increased both [Ca(2+)](i) and tension, these increases being abolished by extracellular Ca(2+) removal and reduced by about 50% by the L-type Ca(2+) channel blocker nifedipine (0.3 microM). Non-L-type Ca(2+) entry through store-operated channels was studied by inhibiting the sarcoplasmic reticulum Ca(2+)-ATPase with cyclopiazonic acid (CPA). CPA (30 microM) induced variable phasic contractions that were abolished by extracellular Ca(2+) removal and by the store-operated channels antagonist 2-aminoethoxydiphenyl borate (2-APB, 50 microM) and largely inhibited by nifedipine (0.3 microM). CPA induced a sustained increase in [Ca(2+)](i) that was reduced in a Ca(2+)-free medium. Under conditions of L-type channels blockade, Ca(2+) readmission after store depletion with CPA evoked a sustained and marked elevation in [Ca(2+)](i) not coupled to contraction. 2-APB (50 microM) inhibited the rise in [Ca(2+)](i) evoked by CPA and the nifedipine-insensitive increases in both [Ca(2+)](i) and contraction elicited by phenylephrine. In alpha-toxin-permeabilized penile arteries, activation of G proteins with guanosine 5'-O-(3-thiotriphosphate) and of the alpha(1)-adrenoceptor with phenylephrine both enhanced the myofilament sensitivity to Ca(2+). This Ca(2+) sensitization was reduced by selective inhibitors of PKC, tyrosine kinase (TK), and Rho kinase (RhoK) by 43%, 67%, and 82%, respectively. As a whole, the present data suggest the alpha(1)-adrenergic vasoconstriction in penile small arteries involves Ca(2+) entry through both L-type and 2-APB-sensitive receptor-operated channels, as well as Ca(2+) sensitization mechanisms mediated by PKC, TK, and RhoK. A capacitative Ca(2+) entry coupled to noncontractile functions of the smooth muscle cell is also demonstrated.

Angiotensin II, reactive oxygen species, and Ca2+signaling in afferent arterioles

In afferent arteriolar vascular smooth muscle cells, ANG II induces a rise in cytosolic Ca2+([Ca2+]i) via inositol trisphosphate receptor (IP3R) stimulation and by activation of the adenine diphosphate ribose (ADPR) cyclase to form cyclic ADPR, which sensitizes the ryanodine receptor (RyR) to Ca2+. We hypothesize that ANG II stimulation of NAD(P)H oxidases leads to the formation of superoxide anion (O2−·), which, in turn, activates ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca2+]i. ANG II rapidly increased [Ca2+]iby 124 ± 12 nM. In the presence of apocynin, a specific inhibitor of NAD(P)H oxidase assembly, the [Ca2+]iresponse was reduced to 35 ± 5 nM ( P < 0.01). Tempol, a superoxide dismutase mimetic, did not alter the [Ca2+]iresponse to ANG II at a concentration of 10−4M (99 ± 12 nM), but 10−3M tempol reduced the response to 32 ± 3 nM ( P < 0.01). The addition of nicotinamide, an inhibitor of ADPR cyclase, to apocynin or tempol (10−3M) resulted in no further inhibition. Measurement of superoxide production with the fluorescent probe tempo 9-AC showed that ANG II caused an increase of 48 ± 20 arbitrary units; apocynin or diphenyl iodonium (an inhibitor of flavoprotein oxidases) inhibited the response by 94%. Hydrogen peroxide (H2O2) was studied at physiological (10−7M) and higher concentrations. In the presence of H2O2(10−7M), neither baseline [Ca2+]inor the response to ANG II was altered (125 ± 15 nM), whereas H2O2(10−6and 10−5M) inhibited the [Ca2+]iresponse to ANG II by 35 and 46%, respectively. We conclude that ANG II rapidly activates NAD(P)H oxidases of afferent arterioles, leading to the formation of O2−·, which then stimulates ADPR cyclase to form cADPR. cADPR, by sensitizing the RyR to Ca2+, augments the Ca2+response (calcium-induced calcium release) initiated by activation of the IP3R.

Ca2+ signaling in prothoracicotropic hormone-stimulated prothoracic gland cells of Manduca sexta: evidence for mobilization and entry mechanisms

Prothoracicotropic hormone (PTTH) stimulates ecdysteroidogenesis in lepidopteran prothoracic glands (PGs), thus indirectly controlling molting and metamorphosis. PTTH triggers a signal transduction cascade in PGs that involves an early influx of Ca2+. Although the importance of Ca2+ has been long known, the mechanism(s) of PTTH-stimulated changes in cytoplasmic Ca2+ [Ca2+]i are not yet well understood. PGs from the fifth instar of Manduca sexta were exposed to PTTH in vitro. The resultant changes in [Ca2+]i were measured using ratiometric analysis of a fura-2 fluorescence signal in the presence and absence of inhibitors of specific cellular signaling mechanisms. The phospholipase C (PLC) inhibitor U-73122 nearly abolished the PTTH-stimulated increase in [Ca2+]i, as well as PTTH-stimulated ecdysteroidogenesis and extracellular-signal regulated kinase phosphorylation, thus establishing a role for PLC and implicating inositol trisphosphate (IP3) in PTTH signal transduction. Two antagonists of the IP3 receptor, 2-APB and TMB-8, likewise blocked the [Ca2+]i response by a mean of 92%. We describe for the first time the presence of Ca2+ oscillations in PTTH-stimulated cells in Ca2+-free medium. External Ca2+ entered PG cells via at least two routes: store-operated (capacitative) Ca2+ entry channels and L-type voltage-gated Ca2+ channels. We propose that PTTH initiates a transductory cascade typical of many G-protein coupled receptors, involving both Ca2+ mobilization and entry pathways.

Calmodulin mediates norepinephrine-induced receptor-operated calcium entry in preglomerular resistance arteries

Although L-type voltage-dependent calcium channels play a major role in mediating vascular smooth muscle cell contraction in the renal vasculature, non-L-type calcium entry mechanisms represent a significant component of vasoactive agonist-induced calcium entry in these cells as well. To investigate the role of these non-voltage-dependent calcium entry pathways in the regulation of renal microvascular reactivity, we have characterized the function of store- and receptor-operated channels (SOCs and ROCs) in renal cortical interlobular arteries (ILAs) of rats. Using fura 2-loaded, microdissected ILAs, we find that the L-type channel antagonist nifedipine blocks less than half the rise in intracellular calcium concentration ([Ca(2+)](i)) elicited by norepinephrine. SOCs were activated in these vessels using the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) inhibitors cyclopiazonic acid and thapsigargin and were dose dependently blocked by the SOC antagonists Gd(3+) and 2-aminoethoxydiphenyl borate (2-APB) and the combined SOC/ROC antagonist SKF-96365. Gd(3+) had no effect on the non-L-type Ca(2+) entry activated by 1 microM NE. A low concentration of SKF-96365 that did not affect thapsigargin-induced store-operated Ca(2+) entry blocked 60-70% of the NE-induced Ca(2+) entry. Two different calmodulin inhibitors (W-7 and trifluoperazine) also blocked the NE-induced Ca(2+) entry. These data suggest that in addition to L-type channels, NE primarily activates ROCs rather than SOCs in ILAs and that this receptor-operated Ca(2+) entry mechanism is regulated by calmodulin. Interestingly, 2-APB completely blocked the NE-induced non-L-type Ca(2+) entry, implying that SOCs and ROCs in preglomerular resistance vessels share a common molecular structure.

Enhanced Ca2+ response to AVP in preglomerular vessels from rats with genetic hypertension during different hydration states

Exaggerated arginine vasopressin (AVP)-induced calcium signaling and renal vasoconstriction, characteristic in young spontaneously hypertensive rats (SHR) during euvolemia, are related to greater amounts of V1a receptor mRNA and V1a protein in preglomerular resistance arterioles. The present study determined whether V1a receptor density and calcium signal transduction in the renal vasculature of young SHR is regulated appropriately during physiological changes in hydration state. [3H]AVP ligand binding documented two- to threefold greater density of V1a receptors in euvolemic SHR vs. Wistar-Kyoto (WKY) rats. Parallel changes in V1a receptor density were observed in both strains during chronic water loading (plus approximately 50 fmol/mg) and during dehydration (minus approximately 50 fmol/mg). Affinity was unchanged. Real-time RT-PCR demonstrated that V1a mRNA in preglomerular arterioles was three times greater in euvolemic SHR. Dehydration decreased expression approximately 50% in renal vessels independent of rat strain; water loading increased V1a mRNA. Thus V1a receptor regulation correlated with changes in mRNA in a normal manner in response to chronic changes in AVP concentration, albeit set at a higher level in SHR. In dehydrated animals, AVP increased the cytosolic Ca2+ concentration ([Ca2+]i) by 60 +/- 5 and 112 +/- 13 nM cytosolic Ca2+ in WKY and SHR, respectively (P < 0.01), whereas in hydrated animals the [Ca2+]i increase was 168 +/- 10 and 220 +/- 18 nM, respectively (P < 0.05). In all hydration states, calcium signaling was greater in SHR compared with WKY (P < 0.05). Calcium signaling paralleled changes in the receptor density and mRNA. Mechanisms other than hydration state per se are likely to be responsible for the two- to threefold difference in the V1a receptor density between WKY and SHR in the renal vasculature at the critical age of 6 wk.

Role of protein kinase C in Ca channel blocker-induced renal arteriolar dilation in spontaneously hypertensive rats

The present study examined the role of L-/T-type Ca channels and the interaction between these channels and protein kinase C (PKC) in hypertension. The isolated perfused hydronephrotic rat kidney model was used to visualize directly the renal microvascular effects of L-/T-type Ca channel blockers (nifedipine and mibefradil, respectively). Nifedipine reversed the angiotensin II-induced constriction of afferent, but not efferent, arterioles in kidneys from Wistar-Kyoto rats (WKY), and similar magnitude in dilation was observed in spontaneously hypertensive rats (SHR). Although mibefradil elicited dilation of both arterioles, the afferent arteriolar dilation was less in SHR than in WKY (57+/-5% vs. 80+/-4% reversal at 1 micrommol/L). The pretreatment with staurosporine did not alter the angiotensin II-induced afferent arteriolar constriction in WKY, but attenuated this response in SHR. Furthermore, staurosporine enhanced the nifedipine-induced afferent arteriolar dilation (62+/-3% vs. 50+/-3% reversal at 10 nmol/L), and restored the attenuated afferent arteriolar response to mibefradil in SHR. The pretreatment with thapsigargin (a blocker of IP3-mediated intracellular calcium release) prevented the angiotensin II-induced afferent arteriolar constriction in WKY, but caused a significant constriction of afferent arterioles in SHR and efferent arterioles in WKY and SHR; in this setting, mibefradil did not alter efferent arteriolar tone. In conclusion, although both L-type (nifedipine) and T-type Ca channel blockers (mibefradil) exerted potent vasodilation of rat renal microvessels, these actions were modified by PKC, which determined the afferent arteriolar sensitivity to these blockers in SHR. Furthermore, the enhancement in nifedipine-induced afferent arteriolar dilation by staurosporine in SHR suggests that L-type Ca channel activity is augmented in hypertensive animals.

Endothelin B receptor Ca2+ signaling in shark vascular smooth muscle: participation of inositol trisphosphate and ryanodine receptors

In mammals, endothelin receptors are sub-classified into ET(A) receptors (ET(A)R), which are purely constrictive in vascular smooth muscle (VSM), and ET(B)R, which may produce constriction in VSM or dilatation by stimulating the production of nitric oxide (NO) from endothelial cells. In contrast, previous studies suggested that shark VSM is stimulated exclusively by ET(B)R. The Ca(2+) signaling pathways utilized by shark VSM in response to stimulation by endothelin-1 (ET-1) have not previously been investigated. We measured cytosolic Ca(2+) concentration ([Ca(2+)](i)) in fura-2-loaded VSM of anterior mesenteric artery of Squalus acanthias and show that the ET(B)R agonists IRL 1620 and sarafotoxin S6c (SRX) increase [Ca(2+)](i) in VSM to the same extent as ET-1 and ET(B)R appears to be the only ETR subtype in sharks. To investigate the participation of the inositol trisphosphate (IP(3)) receptors (IP(3)R), we utilized two inhibitors of the mammalian IP(3)R, TMB-8 and 2-APB. In Ca(2+)-free Ringer, these agents inhibit the response to ET(B)R agonist stimulation by 71%. The ryanodine-sensitive receptor (RyR) may be activated by low concentrations of ryanodine, by abrupt local increases of [Ca(2+)](i), (calcium-induced calcium release) or by cyclic adeninediphosphate ribose (cADPR). We employed three inhibitors of activation of the RyR, Ruthenium Red, 8-Br cADPR and high concentrations of ryanodine; these agents blocked the [Ca(2+)](i) response to ET(B)R agonist stimulation by a mean of 39%. These data show for the first time that in VSM of the shark, ET(B)R activation stimulates both IP(3)R and RyR, and that cADPR is involved in RyR activation.

Angiotensin II Ca2+ signaling in rat afferent arterioles: stimulation of cyclic ADP ribose and IP3 pathways

ANG II induces a rise in cytosolic Ca(2+) ([Ca(2+)](i)) in vascular smooth muscle (VSM) cells via inositol trisphosphate receptor (IP(3)R) activation and release of Ca(2+) from the sarcoplasmic reticulum (SR). The Ca(2+) signal is augmented by calcium-induced calcium release (CICR) and by cyclic adeninediphosphate ribose (cADPR), which sensitizes the ryanodine-sensitive receptor (RyR) to Ca(2+) to further amplify CICR. cADPR is synthesized from beta-nicotinamide adenine dinucleotide (NAD(+)) by a membrane-bound bifunctional enzyme, ADPR cyclase. To investigate the possibility that ANG II activates the ADPR cyclase of afferent arterioles, we used inhibitors of the IP(3)R, RyR, and ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca(2+)](i). In Ca(2+)-containing buffer, ANG II increased [Ca(2+)](i) by 125 +/- 10 nM. In the presence of the IP(3)R antagonists TMB-8 and 2-APB, the peak responses to ANG II were reduced by 74 and 81%, respectively. The specific antagonist of cADPR 8-Br ADPR and a high concentration of ryanodine (100 microM) inhibited the ANG II-induced increases in [Ca(2+)](i) by 75 and 69%, respectively. Nicotinamide and Zn(2+) are known inhibitors of the VSM ADPR cyclase. Nicotinamide diminished the [Ca(2+)](i) response to ANG II by 66%. In calcium-free buffer, Zn(2+) reduced the ANG II response by 68%. Simultaneous blockade of the IP(3) and cADPR pathways diminished the [Ca(2+)](i) response to ANG II by 83%. We conclude that ANG II initiates Ca(2+) mobilization from the SR in afferent arterioles via the classic IP(3)R pathway and that ANG II may lead to activation of the ADPR cyclase to form cADPR, which, via its action on the RyR, substantially augments the Ca(2+) response.

Enhanced response to AVP in the interlobular artery from the spontaneously hypertensive rat

Arginine vasopressin (AVP) induces exaggerated intracellular free calcium (Cai2+) responses in preglomerular smooth muscle cells from young spontaneously hypertensive rats (SHR) due to increased density of the AVP V1a receptor. The intention of the present paper was to examine the relative contribution of afferent arterioles (AA) and interlobular artery (ILA) in AVP- and norepinephrine-induced calcium signaling. The kidneys were perfused with agar solution in vivo, and thin cortical slices were enzyme digested to produce isolated agar-filled vascular fragments. Calcium responses were recorded in fura 2-loaded cells by Ca2+ imaging. Diameter changes were measured after AVP stimulation and mRNA for V1a was measured on isolated vessel fragments. SHR had a significantly higher baseline calcium ratio and lower resting diameter compared with normotensive Wistar-Kyoto rats (WKY). Stimulation with AVP (10(-7) M) in ILA fragments from SHR induced a ratio increase of 0.49 +/- 0.09, significantly higher than the ratio increase in AA from SHR (0.20 +/- 0.03, P < 0.01) and in ILA from WKY (0.24 +/- 0.03, P < 0.01). Stimulation with norepinephrine (10(-7) M) induced responses homogeneously distributed between the segments and strains. Nifedipine treatment or removal of external calcium (Cao2+) reduced the norepinephrine-induced peak response. Both norepinephrine- and AVP-induced sustained responses were abolished after Cao2+ removal in SHR and WKY (P < 0.01). Measurements of V1a receptor mRNA on isolated segments showed a threefold increase in ILA from SHR. The present findings indicate that the exaggerated Ca2+ and contractile response to AVP in SHR is mainly mediated through ILA vasoconstriction.

Polycystin-1 activates the calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway

Regulation of intracellular Ca(2+) mobilization has been associated with the functions of polycystin-1 (PC1) and polycystin-2 (PC2), the protein products of the PKD1 and PKD2 genes. We have now demonstrated that PC1 can activate the calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway through Galpha(q) -mediated activation of phospholipase C (PLC). Transient transfection of HEK293T cells with an NFAT promoter-luciferase reporter demonstrated that membrane-targeted PC1 constructs containing the membrane proximal region of the C-terminal tail, which includes the heterotrimeric G protein binding and activation domain, can stimulate NFAT luciferase activity. Inhibition of glycogen synthase kinase-3beta by LiCl treatment further increased PC1-mediated NFAT activity. PC1-mediated activation of NFAT was completely inhibited by the calcineurin inhibitor, cyclosporin A. Cotransfection of a construct expressing the Galpha(q) subunit augmented PC1-mediated NFAT activity, whereas the inhibitors of PLC (U73122) and the inositol trisphosphate and ryanodine receptors (xestospongin and 2-aminophenylborate) and a nonspecific Ca(2+) channel blocker (gadolinium) diminished PC1-mediated NFAT activity. PC2 was not able to activate NFAT. An NFAT-green fluorescent protein nuclear localization assay demonstrated that PC1 constructs containing the C-tail only or the entire 11-transmembrane spanning region plus C-tail induced NFAT-green fluorescent protein nuclear translocation. NFAT expression was demonstrated in the M-1 mouse cortical collecting duct cell line and in embryonic and adult mouse kidneys by reverse transcriptase-PCR and immunolocalization. These data suggest a model in which PC1 signaling leads to a sustained elevation of intracellular Ca(2+) mediated by PC1 activation of Galpha(q) followed by PLC activation, release of Ca(2+) from intracellular stores, and activation of store-operated Ca(2+) entry, thus activating calcineurin and NFAT.

Non-selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP

Throughout the body there are smooth muscle cells controlling a myriad of tubes and reservoirs. The cells show enormous diversity and complexity compounded by a plasticity that is critical in physiology and disease. Over the past quarter of a century we have seen that smooth muscle cells contain--as part of a gamut of ion-handling mechanisms--a family of cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G-protein-coupled receptor activation, membrane stretch, intracellular Ca2+, pH, phospholipid signals and other factors. Progress in understanding the channels has, however, been hampered by a paucity of specific pharmacological agents and difficulty in identifying the underlying genes. In this review we summarize current knowledge of these smooth muscle cationic channels and evaluate the hypothesis that the underlying genes are homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2, and more are likely to be added soon. Some of these TRP proteins respond to a multiplicity of activation signals--promiscuity of gating that could enable a variety of context-dependent functions. We would seem to be witnessing the first phase of the molecular delineation of these cationic channels, something that should prove a leap forward for strategies aimed at developing new selective pharmacological agents and understanding the activation mechanisms and functions of these channels in physiological systems.

P2Y2-receptor-mediated activation of a contralateral, lanthanide-sensitive calcium entry pathway in the human airway epithelium

1. Receptor-mediated calcium entry (RMCE) was examined in well-differentiated cultures of normal human bronchial epithelial cells (HBECs). Changes in intracellular free Ca(2+) ([Ca(2+)](i)) were quantified using fluorescence ratio imaging of Fura-2-loaded cells during perfusion with Ca(2+) mobilizing agonists. 2. Initial studies revealed an agonist potency of ATP=uridine triphosphate (UTP) >ADP=uridine diphosphate, consistent with purinergic activation of an apical P2Y(2)-receptor mediating the increase in [Ca(2+)](i) in HBECs. 3. Apical UTP (30 microm) induced a sustained period of elevated [Ca(2+)](i) between 300 and 600 s following agonist stimulation that extracellular Ca(2+) free studies indicated was dominated by Ca(2+) influx. 4. RMCE was inhibited by 100 nm La(3+) (83+/-3%) or Gd(3+) (95+/-7%) (P<0.005, n=4-11) and was partially attenuated by Ni(2+) (1 mm) (58.7+/-5.0%, P<0.005, n=9). 5. RMCE was also partially sensitive (< 25% inhibition, P<0.01) to the cation channel blockers SKF96365 (30 microm) and econazole (30 microm), but was insensitive to both verapamil (1 microm) and ruthenium red (10 microm). 6. Using either a sided Ca(2+) readdition protocol or unilateral La(3+), established that the RMCE pathway was located exclusively on the basolateral membrane. 7. The pharmacological sensitivity of the P2Y(2)-receptor activated Ca(2+) entry pathway in the human airway epithelium is inconsistent with the established profile of TRP channel families and is therefore likely to be of an as-yet uncharacterized molecular identity.

Endothelin A and B receptors of preglomerular vascular smooth muscle cells

BACKGROUND

The endothelin (ET) receptors are subclassified into ET(A,) which are purely vasoconstrictive, and ET(B). The ET(B) receptors may cause either vasodilation by stimulating the release of nitric oxide from endothelial cells, or vasoconstriction of vascular smooth muscle cells (VSMC). The relative contribution of ET(A) and ET(B) receptors to calcium signaling and vasoconstriction in the renal microcirculation is not clear. Our goal was to study the cytosolic calcium concentration ([Ca(2+)](i)) responses of fresh rat preglomerular VSMC and afferent arterioles to agonists and antagonists of ET(A) and ET(B) receptors in rats.

METHODS

Fresh VSMC and afferent arterioles were isolated using the magnetized microsphere/sieving technique, followed by gentle collagenase digestion. [Ca(2+)](i) was measured with fura-2 ratiometric fluorescence.

RESULTS

Afferent arterioles and VSMC responded to ET-1 stimulation with a rapid peak increase in [Ca(2+)](i) (Delta= 287 +/- 81 and 342 +/- 55 nmol/L, respectively). The ET(B) receptor agonist IRL 1620 stimulated a rise in [Ca(2+)](i) in afferent arterioles (106 +/- 35 nmol/L); subsequent addition of ET-1 at the IRL 1620 nadir to stimulate ET(A) receptors caused a second peak that was twice as large (213 +/- 44 nmol/L). In VSMC, the ET(B) agonist peak increase was 99 +/- 12 nmol/L; addition of ET-1 then increased [Ca(2+)](i) by 294 +/- 23 nmol/L. The ET(B) inhibitor BQ-788 prevented stimulation of [Ca(2+)](i) by IRL 1620 in afferent arterioles and VSMC; subsequent stimulation of ET(A) receptors with ET-1 caused an increase in [Ca(2+)](i) (239 +/- 17 and 248 +/- 22 nmol/L). Pretreatment with the selective ET(A) inhibitor PD 156707 attenuated but did not abolish the responses to ET-1, suggesting that the residual [Ca(2+)](i) response was caused by ET(B) stimulation.

CONCLUSION

These results indicate that fresh preglomerular VSMC as well as afferent arterioles have both ET(A) and ET(B) receptors, and that the rapid peak [Ca(2+)](i) responses to the ET(B) agonist IRL 1620 are less than half that of subsequent stimulation of ET(A) receptors with ET-1. The similarity of findings in isolated VSMC and afferent arterioles suggests that responses in VSMC in our arteriolar preparation overshadow any potential contribution of endothelial cells when reagents are administered abluminally.

Cellular Mechanism for Mibefradil-Induced Vasodilation of Renal Microcirculation

Although nifedipine and other conventional calcium antagonists elicit preferential vasodilation of renal afferent arterioles, we demonstrate that mibefradil and nickel, T-type calcium channel blockers, reverse the angiotensin II-induced constriction of both afferent and efferent arterioles. Since the angiotensin II-induced vasoconstriction involves inositol trisphosphate (IP3)-induced calcium release from the sarcoplasmic reticulum in the afferent arteriole, and both IP3- and protein kinase C (PKC)-mediated pathways in the efferent arteriole, we investigated the cellular mechanism for the mibefradil-induced dilation of angiotensin II-constricted renal arterioles, using the isolated perfused hydronephrotic rat kidney. Mibefradil caused a dose-dependent dilation of angiotensin II-constricted afferent and efferent arterioles, with 88 +/- 9% and 74 +/- 10% reversal observed at 1 micromol/L, respectively. The blockade of PKC by staurosporine did not alter the mibefradil-induced vasodilator responses of either arterioles (P > 0.5). In contrast, the pretreatment with thapsigargin, which predominantly blocked the IP3-mediated intracellular calcium release, prevented the afferent arteriolar constrictor response to angiotensin II, but caused a significant constriction of efferent arterioles. The subsequent addition of mibefradil had no effect on the efferent arteriolar diameter. Furthermore, the efferent arteriolar constriction induced by direct PKC activation by phorbol myristate acetate was refractory to mibefradil, but completely reversed by LOE908, a nonselective cation channel blocker. In summary, mibefradil markedly dilates the angiotensin II-induced renal arteriolar constriction; the action of mibefradil is most likely mediated by the inhibition of the IP3-mediated pathway, but the inhibitory action on the PKC pathway appears modest.