The action of cysteinyl-leukotrienes on intracellular calcium mobilization in human detrusor myocytes

Can montelukast sodium be an alternative treatment in the treatment of interstitial cystitis?

Background

The leukotriene D4 receptors have been detected in human bladder detrusor myocytes, and they can play the role of interstitial cystitis etiology.

Aim

Our study aims to explain the role of mast cells histologically and immunohistochemically in the pathogenesis and the effectiveness of montelukast that leukotriene D4 receptor antagonist in the treatment of interstitial cystitis.

Subjects and Methods

Twenty-four Wistar albino adult female rats were used. Group 1 (n = 8): control (sham) group, Group 2 (n = 8): interstitial cystitis group, and Group 3 (n = 8): treatment group. Groups 2 and 3 rats were administered 75 mg/kg cyclophosphamide four times every three days intraperitoneally. The rats in the treatment group were started on montelukast sodium as 10 mg/kg, 1 × 1/day per orally after the last administration of cyclophosphamide and were given for 14 days. Mast cells in the bladder tissues were examined histologically, and the presence of IL-6, 8, VEGF, and TNF alpha was examined immunohistochemically.

Results

Thin transitional epithelium, loose connective tissue, weak smooth muscle bundles, and signs of chronic inflammation were observed in the interstitial cystitis group. Regenerated transitional epithelium, intact basement membrane, compact lamina propia, thick smooth muscle bundles, and rare inflammatory cells were observed after the treatment with the montelukast. Mast cells were decreased in bladder tissue after treatment. IL-6, IL-8, VEGF, and TNF alpha levels were significantly decreased after treatment.

Conclusions

We found that inflammatory mediators were significantly reduced after treatment with montelukast in the interstitial cystitis group. Montelukast can be used as an effective drug in the treatment of interstitial cystitis.

Modulation of autophagy and transient receptor potential vanilloid 4 channels by montelukast in a rat model of hemorrhagic cystitis

AIMS

Hemorrhagic cystitis (HC) is a major urotoxic complication of cyclophosphamide (CPA) therapy. This study investigated the uroprotective effect of montelukast on CPA-induced HC, compared to the efficacy of 2-mercaptoethane sulfonate sodium (MESNA).

MAIN METHODS

Male albino rats were pretreated with MESNA (40 mg/kg/day, IP) or montelukast (10 mg/kg/day, orally) for three days then received a single dose of CPA (200 mg/kg, IP), 1 h after the last dose, and compared to CPA-treated rats receiving drug vehicle. Age-matched rats were used as controls. Bladders of rats were assessed biochemically, macroscopically and microscopically by light and electron microscope 24 h later.

KEY FINDINGS

CPA injection contributed to increased bladder weight, urothelial ulceration, vascular congestion, hemorrhage, increased collagen deposition and mast cell infiltration, compared to control rats. Montelukast preconditioning suppressed mast cell infiltration and inflammatory mediators to greater extent than MESNA. Also, montelukast enhanced autophagosomes formation in detrusor myocytes and up-regulated the autophagy-related proteins (beclin-1 & LC3-II), likely through inhibition of phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway. Montelukast preconditioning offset the up-regulation of transient receptor potential vanilloid 4 (TRPV4) in urothelial tissue of CPA-treated rats, to greater extent than MESNA.

SIGNIFICANCE

These results demonstrate the uroprotective effect of montelukast on CPA-induced HC, which appears to be more superior to MESNA. These findings suggest that montelukast can emerge as a novel strategy to protect against CPA-induced urotoxicity.

Painful Bladder Syndrome/Interstitial Cystitis Successful Treatment with Montelukast: A Case Report and Literature Review

Painful bladder syndrome/interstitial cystitis (PBS/IC) is a chronic condition characterized by pelvic pain, urinary frequency, and urgency for more than six months in the absence of urinary tract infections. The etiology of PBS/IC is still an enigma. PBS/IC is challenging for doctors to diagnose because its symptoms overlap with other diseases such as urinary tract infection, overactive bladder, or endometriosis. Hence, it is diagnosed after excluding those diseases. The prognosis of PBS/IC may vary because of multiple treatment options. In this study, we are documenting a 26-year-old female patient who was successfully treated with montelukast after diagnosed with PBS/IC.

Pharmacokinetic considerations for therapies used to treat interstitial cystitis

INTRODUCTION

Interstitial cystitis (IC) or bladder pain syndrome (BPS) is defined as supra-pubic pain related to bladder filling. IC is characterized by a particular symptom complex with no identifiable causes; as with bladder hypersensitivity it is usually associated with urinary frequency and urgency with bladder pain. No current treatments have a significant impact on symptoms over time.

AREAS COVERED

This systematic review examines the pharmacokinetic aspects and adverse event of present IC therapy to highlight appropriate treatment to improve the symptoms of IC. This article reviews material obtained via Medline, PubMed, and EMBASE literature searches up to October 2013.

EXPERT OPINION

The correct approach to IC should consider a multidisciplinary team of specialists and a multimodal treatment package that include psychotherapy, behavior change, physical activation, and analgesic treatment. Unfortunately, a single therapeutic target for IC is not yet known. With regard to pathophysiology and therapy, there is more to discover. The first insult damages the bladder urothelium, hence vehicles that lead the drug to penetrate the wall of the bladder might be a novel strategic approach.

Role of inflammation in bladder function and interstitial cystitis

Cystitis, or inflammation of the bladder, has a direct effect on bladder function. Interstitial cystitis is a syndrome characterized by urinary bladder pain and irritative symptoms of more than 6 months duration. It commonly occurs in young to middle-aged women with no known cause and in fact represents a diagnosis of exclusion. Many factors have been suggested, including chronic or subclinical infection, autoimmunity and genetic susceptibility, which could be responsible for initiating the inflammatory response. However, a central role of inflammation has been confirmed in the pathogenesis of interstitial cystitis. Patients with interstitial cystitis are usually managed with multimodal therapy to break the vicious cycle of chronic inflammation at every step. Patients who develop irreversible pathologies such as fibrosis are managed surgically, which is usually reserved for refractory cases.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Cysteinyl Leukotriene D 4 Increases Human Detrusor Muscle Responsiveness to Histamine

PURPOSE

Leukotriene D(4) and histamine are proinflammatory mediators that are released concomitantly by activated mast cells. There is the possibility of mutual potentiation of their actions in inflammatory diseases such as interstitial cystitis. We investigated whether human detrusor smooth muscle cells showed increased responsiveness to histamine in the presence of leukotriene D(4).

MATERIALS AND METHODS

Cold cup detrusor biopsies were obtained from patients undergoing cystoscopy for benign noninvasive bladder diseases. Human detrusor smooth muscle cells in culture were obtained using an explantation technique and subcultivated for a maximum of 3 passages. The cytosolic free Ca(2+) concentration and contractile force were measured by spectrofluorometry and myograph techniques, respectively.

RESULTS

Low doses of leukotriene D(4) (10 nM or less), which usually do not produce a significant effect on the free Ca(2+) concentration or on muscle contraction when administered 30 to 60 seconds beforehand, significantly enhanced the transient increase in the free Ca(2+) concentration and isometric force induced by 50 to 200 nM histamine. Increased histamine responses were associated with an upward shift in the fura-2 fluorescence ratio, suggesting that histamine hyperresponsiveness was due to the appearance of additional histamine receptors on the sarcolemma or to more efficient signaling per receptor. Leukotriene D(4) concentrations greater than 10 nM had no potentiating effects.

CONCLUSIONS

To our knowledge this is the first demonstration in the human detrusor that leukotriene D(4) potentiates the effect of histamine. These inflammatory mediators, which are often released concomitantly from mast cells, may interact mutually to potentiate the spasmogenic effect of histamine. These results suggest that the combination of leukotriene D(4) and histamine H1 receptor antagonists may be more effective for the treatment of interstitial cystitis than when given alone.

Interleukin-4 and 13 Induce the Expression and Release of Monocyte Chemoattractant Protein 1, Interleukin-6 and Stem Cell Factor From Human Detrusor Smooth Muscle Cells: Synergy With Interleukin-1β and Tumor Necrosis Factor-α

PURPOSE

Interstitial cystitis is characterized by an increased number of activated MCs in the detrusor muscle. However, to our knowledge the factors that influence the anatomical relationship between MCs and HDSMCs are unknown. MCP-1, IL-6 and SCF have a critical role in the regulation of MC development, signaling and function. We investigated whether HDSMCs are capable of expressing and releasing MCP-1, IL-6 and SCF in response to IL-4, IL-13, IL-1beta and tumor necrosis factor-alpha.

MATERIALS AND METHODS

HDSMCs were isolated and cultured using an explant technique. Protein expression, and the secretion of MCP-1, IL-6 and SCF were assayed by semiquantitative reverse transcriptase-polymerase chain reaction and specific enzyme-linked immunosorbent assay.

RESULTS

Unstimulated cells released low amounts of MCP-1, IL-6 and SCF. In cells stimulated by IL-4 MCP-1 mRNA was up-regulated by a mean factor +/- SD of 3.5 +/- 1.3, IL-6 mRNA was up-regulated by 3.8 +/- 1.3, the soluble form of SCF was up-regulated by 3.2 +/- 0.6 and the membrane bound form of SCF was up-regulated by 7.9 +/- 5.6. For IL-13 stimulated cells the values were 2.6 +/- 1.5, 3.6 +/- 2.1, 2.9 +/- 1.6 and 5.7 +/- 3.7, respectively. Soluble SCF mRNA expression was 5 times higher than the expression of mSCF mRNA. IL-4 and IL-13 given separately stimulated MCP-1, IL-6 and SCF secretion in a concentration (0.01 to 100 ng/ml) and time (0 to 24 hours) dependent manner. Furthermore, IL-1beta and tumor necrosis factor-alpha alone induced significant release of MCP-1, IL-6 and SCF but in combination with IL-4 or IL-13 it induced greater secretion of MCP-1, IL-6 and SCF.

CONCLUSIONS

To our knowledge these findings demonstrate for the first time that HDSMCs express and release MCP-1 and IL-6, and show relatively high expression of soluble SCF. This supports our hypothesis that HDSMCs may have an active role by orchestrating the local inflammatory response in the bladder wall with possible implications for the pathophysiology of detrusor mastocytosis.

Human detrusor smooth muscle cells release interleukin-6, interleukin-8, and RANTES in response to proinflammatory cytokines interleukin-1β and tumor necrosis factor-α

OBJECTIVES

Recently, we have demonstrated that human detrusor smooth muscle cells in culture secrete the chemokine monocyte chemoattractant protein 1. In the present study, we extended these studies to include the effect of the proinflammatory cytokines tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta on IL-8, IL-6, and RANTES (regulated on activation, normal T cell expressed and secreted) release by human detrusor smooth muscle cells (HDSMCs) and examined their regulation.

METHODS

With ethical approval, detrusor muscle biopsies were obtained from patients with benign noninvasive bladder diseases undergoing control cystoscopy. HDSMCs were cultured using an explant technique and used at maximum third passage. HDSMCs were cultured in the presence or absence of TNF-alpha and IL-1beta. Supernatants were collected after 6, 12, and 24 hours. IL-8, IL-6, and RANTES were measured using enzyme-linked immunosorbent assays.

RESULTS

TNF-alpha and IL-1beta (0.01 to 100 ng/mL) induced secretion of IL-8, IL-6, and RANTES in a dose and time-dependent manner. The production of chemokines reached a maximum after 24 hours of incubation. In nonstimulated HDSMCs, the basal secretion of IL-8, IL-6, and RANTES was detectable. Induction of cytokine release by IL-1beta was synergistic with TNF-alpha.

CONCLUSIONS

These findings for the first time demonstrate that HDSMCs release IL-8, IL-6, and RANTES in response to IL-1beta and TNF-alpha. The constitutive and cytokine-stimulated production of chemokines and cytokines suggest that the human detrusor may contribute to mast cell infiltration into the bladder interstitium. The new evidence that HDSMCs secrete immunomodulatory proteins makes the detrusor muscle cell a target for anti-inflammatory therapy.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Monocyte chemoattractant protein-1 production by human detrusor smooth muscle cells

PURPOSE

Most recently attention has turned to the secretory properties of smooth muscle cells. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that causes mast cells recruitment and provokes mast cells activation in vitro. We investigated whether MCP-1 is produced by human detrusor smooth muscle cells (HDSMCs) cultured under inflammatory conditions.

MATERIALS AND METHODS

Using an explantation technique HDSMCs were isolated and short-term cultured. HDSMCs were incubated at 37C for 24 hours with the proinflammatory mediators interleukin-1 beta (IL-1 beta), tumor necrosis factor (TNF-alpha), lipopolysaccharide, histamine, leukotriene D4 and prostaglandin E2. The level of MCP-1 in cell supernatants were measured by enzyme linked immunoassay.

RESULTS

There was basal secretion of MCP-1 in unstimulated cultures. Following 24-hour incubation with IL-1 beta or TNF-alpha (1 pg/ml to 100 ng/ml) the level of MCP-1 increased in a dose dependent manner. IL-1 beta was more potent at inducing MCP-1 release in 8 of 10 experiments. Lipopolysaccharide (10 microg/ml), histamine (100 microM), leukotriene D4 (50 nM), prostaglandin E2 (1 microM) and KCl (30 to 100 mM) failed to induce MCP-1 production. When IL-1 beta (10 ng/ml) and TNF-alpha (10 ng/ml) were given in combination, a highly synergistic effect on MCP-1 production was observed.

CONCLUSIONS

To our knowledge this study shows for the first time that human detrusor smooth muscle cells cultivated under inflammatory conditions produce significant amounts of MCP-1. In addition to contractile function, HDSMCs have synthesis and secretory potential with the release of MCP-1. Thus, MCP-1 may contribute to the local inflammatory process by producing proinflammatory mediators. The release of cytokines and chemokines by human detrusor muscle even in small amounts may have important functional consequences.

Effect of bladder outlet obstruction on detrusor smooth muscle cell: an in vitro study 1, 2 1Presented at the 6th Asian Congress of Urology (6th ACU), Kuala Lumpur, Malaysia, August 12–18, 2002 2This study was supported by a grant from National Natural Science Fund (No. 39970739), China, PRC

BACKGROUND

Although relieving obstruction is generally curative on bladder outlet obstruction (BOO), bladder dysfunction persists in some patients. Repetitive stretch and relaxation applied to cultured bladder smooth muscle (SM) cells in vitro have been used to mimic increases in urodynamic load experienced by the detrusor muscle under conditions of BOO. We first clarified the relationship between phenotype transformation and biomechanical properties of detrusor smooth muscle cell (DSMC) subjected to the cyclic mechanical stretch.

MATERIALS AND METHODS

Cultured rat DSMC were grown on collagen-coated silicone membranes and subjected to continuous cycles of stretch-relaxation. All experiments were performed on cells between passages 2 and 4. Each cycle consists of 5 seconds of stretch and 5 seconds of relaxation. The computer controlled vacuum induced 10% (1), 20% (2), and 30% (3) maximum elongation of the plate membrane at different designed pressures. The deoxyribonucleic acid synthesis rate was assessed by performing tritiated thymidine incorporation assay. The expression of SM-alpha-actin and proliferation of DSMC were analyzed by immunofluorescent assay and flow cytometry. The image analysis and micropipet aspiration systems were used to investigate the single cell contraction and viscoelasticity. Using the 3-element standard linear solid model, the elastic modulus K(1), K(2), and viscoelastic coefficient mu were determined, which show the passive deformation ability of detrusor cells.

RESULTS

As the basic structural changes to mechanical stretch, DSMC undergo phenotypic modulation from their normal contractile phenotype to a "synthetic" phenotype: the DSMC become more proliferative and the actin less organized along the cell's long axis. The cell proliferation index of control and stretched group (10%, 20%, 30% elongation) are 0.24, 0.43, 0.58, and 0.65, respectively. The actin filaments in unstimulated cells were evident and orientated along the major axis of the cell. After mechanical stretch, the well-spread filaments changed their orientation. The function, such as contraction, and viscoelasticity of a single DSMC subjected to stretch both decreased significantly compared with control. The maximum contractile velocity and maximum cell length shortening rate of group 3 (30% elongation) showed significant decreases compared with unstretched control (P < 0.01). K(1) and K(2) were decreased with the increase of mechanical overload. However, there was no statistic difference between groups 2 and 3.

CONCLUSIONS

Functional abnormalitie of BOO have the structural basis: phenotype transformation (i.e., remodeling) of the detrusor cells. Cyclic stretch and relaxation applied to DSMC in vitro can be used to model increases in urodynamic load experienced by the bladder detrusor muscle under conditions of BOO. Phenotype transformation is the structural basis of functional changes of DSMC subjected to periodic overload mechanical stretch.

The cysteinyl-leukotriene D4 induces cytosolic Ca2+ elevation and contraction of the human detrusor muscle

PURPOSE

The role of intracellular Ca2+ in the activation of human detrusor smooth muscle cells (SMCs) is pivotal. Recently we showed that the mast cell derived pro-inflammatory mediator leukotriene D(4) (LTD(4)) induces increase in intracellular free Ca2+ ([Ca2+](i)) in human detrusor myocytes. In the current study we examined the mechanisms underlying LTD(4) induced increase in [Ca2+](i) and tested whether LTD(4) induces muscle contraction by measuring force development in human detrusor tissue.

MATERIALS AND METHODS

Cultures of human detrusor SMCs were obtained from patients with benign bladder diseases undergoing cystoscopy. [Ca2+](i) was measured in fura-2 loaded SMCs using micro-spectrofluorometry and dynamic video imaging. Contractile force was monitored with an especially built mini-myograph.

RESULTS

Spontaneous oscillations in [Ca2+](i) and force were observed. In the absence of calcium these oscillations were absent. LTD(4) caused a concentration dependent increase in [Ca2+](i) and isometric force. Calcium was released exclusively from intracellular stores. Increases in [Ca2+](i) and force were inhibited in dose dependent fashion by the LTD(4) receptor antagonists montelukast and zafirlukast. Likewise, LTC(4) and LTE(4) induced an increase in [Ca2+](i) and contractile force in the rank order LTD(4) >LTC(4) >LTE(4). Inhibition of Ca2+ induced Ca2+ release (CICR) with thapsigargin and ryanodine suggested the presence of a functional CICR in SMCs.

CONCLUSIONS

To our knowledge this study demonstrates for the first time that the cysteinyl-leukotriene LTD(4) induces contraction in human detrusor SMCs. LTD(4) induced force and increased [Ca2+](i) were entirely dependent on Ca2+ release from intracellular stores. The action of LTD(4) on force development and increased [Ca2+](i) appeared to be specific, mediated by the binding and activation of specific LTD(4) receptors on SMCs. Also, to our knowledge this report is the first to show that human detrusor SMCs are sensitive to ryanodine, consistent with the hypothesis that a CICR is present and functional in these cells. The presence and role of endogenous cysteinyl leukotrienes for normal contractile functioning of the human detrusor during inflammation remains to be elucidated.

Recent developments in the management of interstitial cystitis

PURPOSE OF REVIEW

Interstitial cystitis, a great enigma of urology today, is a chronic sterile inflammatory disease of the bladder of unknown etiology characterized by urinary frequency, urgency, nocturia and suprapubic pain. Although there are plenty of theories, the etiology of the condition remains obscure. This review focuses on recently published literature on interstitial cystitis.

RECENT FINDINGS

Several pathophysiological mechanisms have been proposed in the past few years including epithelial dysfunction, activation of mast cells, neurogenic inflammation, autoimmunity and occult infection. Evidence indicates that it is a heterogeneous syndrome and that the two subtypes, classic and nonulcer disease, represent different entities. The diagnosis is made by clinical and cystoscopic evaluation with hydrodistension and often with biopsy when other disorders are excluded. The National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases has developed criteria for clinical studies. There is a need for a noninvasive marker of interstitial cystitis. Antiproliferative factor as a urinary marker has shown promising results. The value of the bladder permeability test in interstitial cystitis needs further investigation. Many gynecologic conditions mimic the symptoms of interstitial cystitis. Multiple forms of therapy are available including self-care and dietary changes, medical and intravesical treatments, neuromodulation, multimodality treatment and surgical intervention. It is recommended that the most conservative treatments are used first and surgery should be regarded as the last resort.

SUMMARY

Interstitial cystitis is a challenging disease of urology today. While causative factors remain unknown, treatment is based on empiricism. Intensive research may result in new and hopefully more effective treatments in the future.

Cysteinyl leukotriene-dependent [Ca2+]i responses to angiotensin II in cardiomyocytes

With the use of fura 2 measurements in multiple and single cells, we examined whether cysteinyl leukotrienes (CysLT) mediate angiotensin II (ANG II)-evoked increases in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in neonatal rat cardiomyocytes. ANG II-evoked CysLT release peaked at 1 min. The angiotensin type 1 (AT(1)) antagonist losartan, but not the AT(2) antagonist PD-123319, attenuated the elevations in [Ca(2+)](i) and CysLT levels evoked by ANG II. Vasopressin and endothelin-1 increased [Ca(2+)](i) but not CysLT levels. The 5-lipoxygenase (5-LO) inhibitor AA-861 and the CysLT(1)-selective antagonist MK-571 reduced the maximal [Ca(2+)](i) responses to ANG II but not to vasopressin and endothelin-1. While MK-571 reduced the responses to leukotriene D(4) (LTD(4)), the dual CysLT antagonist BAY-u9773 completely blocked the [Ca(2+)](i) elevation to both LTD(4) and LTC(4). These data confirm that ANG II-evoked increases, but not vasopressin- and endothelin-1-evoked increases, in [Ca(2+)](i) involve generation of the 5-lipoxygenase metabolite CysLT. The inositol (1,4,5)-trisphosphate [Ins(1,4,5)P(3)] antagonist 2-aminoethoxydiphenyl borate attenuated the [Ca(2+)](i) responses to ANG II and LTD(4). Thus AT(1) receptor activation by ANG II is linked to CysLT-mediated Ca(2+) release from Ins(1,4,5)P(3)-sensitive intracellular stores to augment direct ANG II-evoked Ca(2+) mobilization in rat cardiomyocytes.

Voltage independence of vasomotion in isolated irideal arterioles of the rat

The cellular mechanisms underlying vasomotion of irideal arterioles from juvenile rats have been studied using electrophysiological methods, ratiometric calcium measurements and video microscopy. Vasomotion was not affected by removal of the endothelium. Spontaneous contractions were preceded by spontaneous depolarizations. Both were abolished by the intracellular calcium chelator, BAPTA AM (20 microM), but not by ryanodine (10 microM), suggesting a dependence on the cyclical release of calcium from intracellular stores, other than those operated by ryanodine receptors. Oscillations were little changed when the membrane potential of short segments of arteriole was either depolarized or hyperpolarized. When the segments were voltage clamped, oscillating inward currents were recorded, indicating that the changes in membrane potential were voltage independent. Vasomotion was preceded by intracellular calcium oscillations and both were abolished by inhibitors of phospholipase C (U73122, 10 microM), phospholipase A(2) (AACOCF(3), 30 microM) and protein kinase C (chelerythrine chloride, 5 microM, and myristoylated protein kinase C peptide, 10 microM). Inhibition of vasomotion by the dual lipoxygenase and cyclo-oxygenase inhibitor, NDGA (10 microM), the lipoxygenase inhibitor, ETI (1 microM) but not by the cyclo-oxygenase inhibitors, aspirin (10 microM) and indomethacin (10 microM), or the cytochrome P450 inhibitor 17-ODYA (10 microM), suggested an involvement of the lipoxygenase pathway. The observations suggest that vasomotion of iris arterioles is voltage independent and results from the cyclical release of calcium from IP(3)-sensitive stores which are activated by cross talk between the phospholipase C and phospholipase A(2) pathways in vascular smooth muscle.