Newly emerging Ca2+ entry channel molecules that regulate the vascular tone

Local blood flow is critically determined by the arterial tone in which sustained Ca²⁺ influx, activated by a variety of mechanisms, plays a central regulatory role. Recent progress in molecular biological research has disclosed unexpectedly diverse and complex facets of Ca²⁺ entry channel molecules involved in this Ca²⁺ influx. Candidates include several transient receptor potential (TRP) superfamily members such as TRPC1, TRPC4, TRPC6, TRPV2, TRPV4 and TRPM4, none of which exhibit simple properties attributable to a single particular role. Rather, they appear to be multimodally activated or modulated by receptor stimulation, temperature, mechanical stress or lipid second messengers generated from various sources, and may be involved in both acute vasomotor control and long-term vascular remodelling. This paper provides an overview of existing knowledge of TRP proteins, and their possible relationships with principal factors regulating the arterial tone (i.e., autonomic nerves, various autocrine and paracrine factors, and intravascular pressure).     

TRP channels in lymphocytes

TRP proteins form ion channels that are activated following receptor stimulation. Several members of the TRP family are likely to be expressed in lymphocytes. However, in many studies, messenger RNA (mRNA) but not protein expression was analyzed and cell lines but not primary human or murine lymphocytes were used. Among the expressed TRP mRNAs are TRPC1, TRPC3, TRPM2, TRPM4, TRPM7, TRPV1, and TRPV2. Regulation of Ca2+ entry is a key process for lymphocyte activation, and TRP channels may both increase Ca2+ influx (such as TRPC3) or decrease Ca2+ influx through membrane depolarization (such as TRPM4). In the future, linking endogenous Ca2+/cation channels in lymphocytes with TRP proteins should lead to a better molecular understanding of lymphocyte activation.     

Transient receptor potential channel activation and endothelium-dependent dilation in the systemic circulation

The endothelium plays a crucial role in the regulation of vascular tone by releasing a number of vasodilator mediators, including nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor(s). The production of these mediators is typically initiated by an increase in intracellular Ca(2+) concentration ([Ca(2+)]i) in endothelial cells. An essential component of this Ca(2+) signal is the entry of Ca(2+) from the extracellular space through plasma membrane Ca(2+)-permeable channels. Although the molecular identification of the potential Ca(2+) entry channel(s) responsible for the release of endothelial relaxing factors is still evolving, accumulating evidence indicates that the transient receptor potential (TRP) channels, a superfamily of Ca(2+)-permeable cation channels, serve as an important mechanism of Ca(2+) entry in endothelial cells and other nonexcitable cells. The activation of these channels has been implicated in diverse endothelial functions ranging from control of vascular tone and regulation of vascular permeability to angiogenesis and vascular remodeling. This review summarizes recent evidence concerning TRP channels and endothelium-dependent dilation in several systemic vascular beds. In particular, we highlight the emerging roles of several TRP channels from the canonical and vanilloid subfamilies, including TRPV4, TRPC4, and TRPC6, in vasodilatory responses to shear stress and receptor agonists and discuss potential signaling mechanisms linking the TRP channel activation and the initiation of endothelium-derived hyperpolarizing factor-mediated responses in endothelial cells.     

Transient receptor potential (TRP) channels, vascular tone and autoregulation of cerebral blood flow

Members of the transient receptor potential (TRP) channel superfamily are present in vascular smooth muscle cells and play important roles in the regulation of vascular contractility. The TRPC3 and TRPC6 channels are activated by stimulation of several excitatory receptors in vascular smooth muscle cells. Activation of these channels leads to myocyte depolarization, which stimulates Ca2+ entry via voltage-dependent Ca2+ channels (VDCC), leading to vasoconstriction. The TRPV4 channels in arterial myocytes are activated by epoxyeicosatrienoic acids, and activation of the channels enhances Ca2+ spark and transient Ca2+-sensitive K+ channel activity, thereby hyperpolarizing and relaxing vascular smooth muscle cells. The TRPC6 and TRPM4 channels are activated by mechanical stimulation of cerebral artery myocytes. Subsequent depolarization and activation of VDCC Ca2+ entry is directly linked to the development of myogenic tone in vitro and to autoregulation of cerebral blood flow in vivo. These findings imply a fundamental importance of TRP channels in the regulation of vascular smooth muscle tone and suggest that TRP channels could be important targets for drug therapy under conditions in which vascular contractility is disturbed (e.g. hypertension, stroke, vasospasm).     

Role of Ca2+ signaling in the regulation of endothelial permeability

The vascular endothelial cell forms a semipermeable barrier between blood and interstitium. Inflammatory mediators such as thrombin and histamine induce vascular leakage defined as increased endothelial permeability to plasma proteins and other solutes. Increased endothelial permeability is the hallmark of inflammatory vascular edema. Inflammatory mediators that bind to heptahelical G protein-coupled receptors (GPCR) trigger increased endothelial permeability by increasing the intracellular Ca(2+) concentration ([Ca(2+)](i)). The rise in [Ca(2+)](i) activates key signaling pathways, which mediate cytoskeletal reorganization (through myosin light chain (MLC)-dependent contraction) and disassembly of VE-cadherin at the adherens junctions. The Ca(2+)-dependent protein kinase C (PKC) isoform, PKC-alpha, plays a critical role in initiating endothelial cell contraction and disassembly of VE-cadherin junctions. The increase in [Ca(2+)](i) induced by a variety of agonists is achieved by the generation of inositol 1,4,5-trisphosphate (IP3), activation of IP3 receptors (IP3R), release of stored intracellular Ca(2+), and Ca(2+) entry through plasma membrane channels. Recent findings demonstrate that IP3-sensitive Ca(2+) store depletion activates plasma membrane cation channels (i.e., store-operated cation channels (SOC) or Ca(2+) release activated channels) to cause Ca(2+) influx in endothelial cells. This mode of Ca(2+) influx is also known as capacitative Ca(2+) entry (CCE). Store-operated Ca(2+) influx signals increase in permeability and nitric oxide (NO) production and provokes changes in gene expression in endothelial cells. Recent studies have established that the Drosophila transient receptor potential (TRP) gene family of channels expressed in endothelial cells can function as SOC. Deletion of one of the TRP homologues, TRPC4, in mouse caused impairment in store-operated Ca(2+) current and Ca(2+) store release activated Ca(2+) influx in aortic and lung endothelial cells (LEC). In TRPC4 knockout (TRPC4(-/-)) mice, acetylcholine-induced endothelium-dependent smooth muscle relaxation was drastically reduced. In addition, TRPC4(-/-) mice LEC exhibited lack of actin stress fiber formation and cell retraction in response to thrombin activation of proteinase-activated receptor-1 (PAR-1) in endothelial cells. The increase in lung microvascular permeability in response to thrombin receptor activation was inhibited in TRPC4(-/-) mice. These results indicate that endothelial TRP channels such as TRPC1 and TRPC4 play an important role in signaling the increase in endothelial permeability.     

TRP channels in normal and dystrophic skeletal muscle

TRP proteins constitute non-selective cation-permeable ion channels, most of which are permeable to Ca2?. In skeletal muscle, several isoforms of the TRPC (Canonical), TRPV (Vanilloid) and TRPM (Melastatin) subfamilies are expressed. In particular, TRPC1, C3 and C6, TRPV2 and V4, TRPM4 and TRPM7 have been consistently found in cultured myoblasts or in adult muscles. These channels seem to directly or indirectly respond to membrane stretch or to Ca2? stores depletion; some isoforms might also constitute unregulated Ca2? leak channels. Their function is largely unknown. TRPC1 and C3 have been involved in muscle development, in particular in myoblasts migration and differentiation. TRPC1 and V4 might allow a basal influx of Ca2? at rest. Their lack has consequences on muscle fatigue. TRPV2 seems to be stretch-sensitive. It localizes mainly in intracellular pools at rest, and translocates to the plasma membrane upon IGF-1 stimulation. TRP channels seem to be involved in the pathophysiology of muscle disorders. In particular in Duchenne muscular dystrophy, the lack of the cytoskeletal protein dystrophin induces a disregulation of several ion channels leading to an abnormal influx of Ca2?. We discuss here, the possible involvement of TRP channels in this abnormal influx of Ca2?.     

TRPC channels: interacting proteins

TRP channels, in particular the TRPC and TRPV subfamilies, have emerged as important constituents of the receptor-activated Ca2+ influx mechanism triggered by hormones, growth factors, and neurotransmitters through activation ofphospholipase C (PLC). Several TRPC channels are also activated by passive depletion of endoplasmic reticulum (ER) Ca2+. Although in several studies the native TRP channels faithfully reproduce the respective recombinant channels, more often the properties of Ca2+ entry and/or the store-operated current are strikingly different from that of the TRP channels expressed in the same cells. The present review aims to discuss this disparity in the context of interaction of TRPC channels with auxiliary proteins that may alter the permeation and regulation of TRPC channels.     

New target molecules in the drug control of blood pressure and circulation

Ion channels play a pivotal role in blood pressure regulation. Amongst them, much attention has been directed to dihydropyridine (DHP)-sensitive (L-type) voltage-dependent Ca(2+) channels (VDCCs) and iberiotoxin-sensitive Ca(2+)-dependent K(+) channels which are distributed over the whole vascular tree and contribute to vascular tone regulation. Recent advances in vascular electrophysiology have, however, added novel and interesting molecules to this repertoire. In small mesenteric arterioles, the predominant VDCC phenotype is not L-type but DHP-insensitive, high voltage-activated VDCCs that exhibit unique properties distinguishable from those of hitherto-known VDCCs. Surprisingly, mibefradil, a well-known T-type selective blocker potently inhibits these channels, and the use of this blocker has indicated that Ca(2+) entry through these channels may be one of the important determinants of peripheral vascular tone. Another new candidate likely involved in blood pressure control is the mammalian homologue of Drosophila transient receptor potential (TRP) protein, including TRPC4 and TRPC6. Experiments in genetically engineered TRPC4-deficient mice have suggested that expression of TRPC4 is indispensable for agonist-induced Ca(2+) entry in endothelial cells and production of nitric oxide and vasorelaxation. TRPC6 is likely to contribute to sustained Ca(2+) entry into vascular smooth muscle cells activated by stimulation of sympathetic nerves and elevation of intravascular pressure. Antisense oligonucleotide experiments have suggested that this protein is an essential component of alpha1-adrenoceptor activated and mechanosensitive cation channels in some vascular tissues. This review overviews what is known about the role of ionic channels in blood pressure control with main focus on the above-mentioned new molecules as promising targets for drug discovery and development.     

Activation of the melastatin-related cation channel TRPM3 by D-erythro-sphingosine [corrected

TRPM3, a member of the melastatin-like transient receptor potential channel subfamily (TRPM), is predominantly expressed in human kidney and brain. TRPM3 mediates spontaneous Ca2+ entry and nonselective cation currents in transiently transfected human embryonic kidney 293 cells. Using measurements with the Ca2+-sensitive fluorescent dye fura-2 and the whole-cell patch-clamp technique, we found that D-erythro-sphingosine, a metabolite arising during the de novo synthesis of cellular sphingolipids, activated TRPM3. Other transient receptor potential (TRP) channels tested [classic or canonical TRP (TRPC3, TRPC4, TRPC5), vanilloid-like TRP (TRPV4, TRPV5, TRPV6), and melastatin-like TRP (TRPM2)] did not significantly respond to application of sphingosine. Sphingosine-induced TRPM3 activation was not mediated by inhibition of protein kinase C, depletion of intracellular Ca2+ stores, and intracellular conversion of sphingosine to sphingosine-1-phosphate. Although sphingosine-1-phosphate and ceramides had no effect, two structural analogs of sphingosine, dihydro-D-erythro-sphingosine and N,N-dimethyl-D-erythro-sphingosine, also activated TRPM3. Sphingolipids, including sphingosine, are known to have inhibitory effects on a variety of ion channels. Thus, TRPM3 is the first ion channel activated by sphingolipids.     

Emerging functions of 10 types of TRP cationic channel in vascular smooth muscle

1. The influx of Ca2+, Mg2+ and Na+ and the efflux of K+ have central importance for the function and survival of vascular smooth muscle cells, but progress in understanding the influx/efflux pathways has been restricted by a lack of identification of the genes underlying many of the non-voltage-gated cationic channels. 2. The present review highlights evidence suggesting the genes are mammalian homologues of the Transient Receptor Potential (TRP) gene of the fruit-fly Drosophila. The weight of evidence supports roles for TRPC1, TRPP2/1 and TRPC6, but recent studies point also to TRPC3, TRPC4/5, TRPV2, TRPM4 and TRPM7. 3. Activity of these TRP channels is suggested to modulate contraction and sense changes in intracellular Ca2+ storage, G-protein-coupled receptor activation and osmotic stress. Roles in relation to myogenic tone, actions of vasoconstrictors substances, Mg2+ homeostasis and the vascular injury response are suggested. 4. Knowledge that TRP channels are relevant to vascular smooth muscle cells in both their contractile and proliferative phenotypes should pave the way for a better understanding of vascular biology and provide the basis for the discovery of a new set of therapeutic agents targeted to vascular disease.     

Psychiatric Disorders and TRP Channels: Focus on Psychotropic Drugs

Psychiatric and neurological disorders are mostly associated with the changes in neural calcium ion signaling pathways required for activity-triggered cellular events. One calcium channel family is the TRP cation channel family, which contains seven subfamilies. Results of recent papers have discovered that calcium ion influx through TRP channels is important. We discuss the latest advances in calcium ion influx through TRP channels in the etiology of psychiatric disorders.Activation of TRPC4, TRPC5, and TRPV1 cation channels in the etiology of psychiatric disorders such as anxiety, fear-associated responses, and depression modulate calcium ion influx. Evidence substantiates that anandamide and its analog (methanandamide) induce an anxiolytic-like effect via CB1 receptors and TRPV1 channels. Intracellular calcium influx induced by oxidative stress has an significant role in the etiology of bipolar disorders (BDs), and studies recently reported the important role of TRP channels such as TRPC3, TRPM2, and TRPV1 in converting oxidant or nitrogen radical signaling to cytosolic calcium ion homeostasis in BDs. The TRPV1 channel also plays a function in morphine tolerance and hyperalgesia. Among psychotropic drugs, amitriptyline and capsazepine seem to have protective effects on psychiatric disorders via the TRP channels. Some drugs such as cocaine and methamphetamine also seem to have an important role in alcohol addiction and substance abuse via activation of the TRPV1 channel.Thus, we explore the relationships between the etiology of psychiatric disorders and TRP channel-regulated mechanisms. Investigation of the TRP channels in psychiatric disorders holds the promise of the development of new drug treatments.     

TRP channels in platelet function

Ca2+ entry forms an essential component of platelet activation; however, the mechanisms associated with this process are not understood. Ca2+ entry upon receptor activation occurs as a consequence of intracellular store depletion (referred to as store-operated Ca2+ entry or SOCE), a direct action of second messengers on cation entry channels or the direct occupancy of a ligand-gated P2(Xi) receptor. The molecular identity of the SOCE channel has yet to be established. Transient receptor potential (TRP) proteins are candidate cation entry channels and are classified into a number of closely related subfamilies including TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin) and TRPML (mucolipins). From the TRPC family, platelets have been shown to express TRPC6 and TRPC1, and are likely to express other TRPC and other TRP members. TRPC6 is suggested to be involved with receptor-activated, diacyl-glycerol-mediated cation entry. TRPC1 has been suggested to be involved with SOCE, though many of the suggested mechanisms remain controversial. As no single TRP channel has the properties described for SOCE in platelets, it is likely that it is composed of a heteromeric association of TRP and related subunits, some of which may be present in intracellular compartments in the resting cell.     

TRP channels in neurogastroenterology: opportunities for therapeutic intervention

The members of the superfamily of transient receptor potential (TRP) cation channels are involved in a plethora of cellular functions. During the last decade, a vast amount of evidence is accumulating that attributes an important role to these cation channels in different regulatory aspects of the alimentary tract. In this review we discuss the expression patterns and roles of TRP channels in the regulation of gastrointestinal motility, enteric nervous system signalling and visceral sensation, and provide our perspectives on pharmacological targeting of TRPs as a strategy to treat various gastrointestinal disorders. We found that the current knowledge about the role of some members of the TRP superfamily in neurogastroenterology is rather limited, whereas the function of other TRP channels, especially of those implicated in smooth muscle cell contractility (TRPC4, TRPC6), visceral sensitivity and hypersensitivity (TRPV1, TRPV4, TRPA1), tends to be well established. Compared with expression data, mechanistic information about TRP channels in intestinal pacemaking (TRPC4, TRPC6, TRPM7), enteric nervous system signalling (TRPCs) and enteroendocrine cells (TRPM5) is lacking. It is clear that several different TRP channels play important roles in the cellular apparatus that controls gastrointestinal function. They are involved in the regulation of gastrointestinal motility and absorption, visceral sensation and visceral hypersensitivity. TRP channels can be considered as interesting targets to tackle digestive diseases, motility disorders and visceral pain. At present, TRPV1 antagonists are under development for the treatment of heartburn and visceral hypersensitivity, but interference with other TRP channels is also tempting. However, their role in gastrointestinal pathophysiology first needs to be further elucidated.     

Vanilloid transient receptor potential cation channels: an overview

The mammalian branch of the Transient Receptor Potential (TRP) superfamily of cation channels consists of 28 members. They can be subdivided in six main subfamilies: the TRPC ('Canonical'), TRPV ('Vanilloid'), TRPM ('Melastatin'), TRPP ('Polycystin'), TRPML ('Mucolipin') and the TRPA ('Ankyrin') group. The TRPV subfamily comprises channels that are critically involved in nociception and thermo-sensing (TRPV1, TRPV2, TRPV3, TRPV4) as well as highly Ca2+ selective channels involved in Ca2+ absorption/reabsorption in mammals (TRPV5, TRPV6). In this review we summarize fundamental physiological properties of all TRPV members in the light of various cellular functions of these channels and their significance in the systemic context of the mammalian organism.     

Canonical transient receptor potential channels in disease: targets for novel drug therapy?

The canonical transient receptor potential (TRPC) channels constitute one of the three major families within the large transient receptor potential (TRP) superfamily. TRPC channels are the closest mammalian homologues of Drosophila TRP, the light-activated channel in Drosophila photoreceptor cells. All TRPC channels (TRPC1-7) are activated via phospholipase-C-coupled receptors and were, therefore, proposed to encode elusive native receptor-activated cation channels in many cell types. A physiological role has been established for all of the known TRPC channels, including the control of vascular tone (TRPC1, TRPC4 and TRPC6) or lymphocyte activation, which is essential for immune competence (TRPC1 and TRPC3). The emergence of TRPC channels in controlling a variety of biological functions offers new and promising targets for drug development.     

Roles of TRP channels in the development of cardiac hypertrophy

Cardiac hypertrophy is induced by various stresses such as hypertension and myocardial infarction. It is believed that hypertrophy is adaptive in the early phase but becomes maladaptive in the late phase. Cardiac hypertrophy develops heart failure when the heart is exposed persistently to the stresses. The increase in intracellular Ca(2+) ([Ca(2+)](i)) plays an important role in the development of hypertrophy. It is generally thought that the increase in [Ca(2+)](i) for hypertrophy occurs via G(q)-stimulated production of inositol-1,4,5-trisphosphate (IP(3)) and IP(3)-mediated release of Ca(2+) from intracellular store. However, several groups recently reported that canonical transient receptor potential (TRPC) channels are responsible for the increase in [Ca(2+)](i). Among them, three TRPC subtypes (TRPC3/TRPC6/TRPC7) are activated by another G(q)-mediated second messenger, diacylglycerol. Although several groups independently demonstrated that TRPC channels mediate receptor-stimulated and pressure overload-induced hypertrophy, there is discrepancy of which subtypes of TRPC channels predominantly mediate hypertrophy. However, there is consensus that TRPC-mediated Ca(2+) influx is essential for hypertrophy. As TRPC channels participate in pathological hypertrophy, but not physiological contraction and the relaxation cycle, TPRC channels are a new target for the treatment of hypertrophy.     

Contractile mechanisms coupled to TRPA1 receptor activation in rat urinary bladder

TRPA1 is a member of the transient receptor potential (TRP) channel family present in sensory neurons. Here we show that vanilloid receptor (TRPV1) stimulation with capsaicin and activation of TRPA1 with allyl isothiocyanate or cinnamaldehyde cause a graded contraction of the rat urinary bladder in vitro. Repeated applications of maximal concentrations of the agonists produce desensitization to their contractile effects. Moreover, contraction caused by TRPA1 agonists generates cross-desensitization with capsaicin. The TRP receptor antagonist ruthenium red (10-100 microM) inhibits capsaicin (0.03 microM), allyl isothiocyanate (100 microM) and cinnamaldehyde (300 microM)-induced contractions in the rat urinary bladder. The selective TRPV1 receptor antagonist SB 366791 (10 microM) blocks capsaicin-induced contraction, but partially reduces allyl isothiocyanate- or cinnamaldehyde-mediated contraction. However, allyl isothiocyanate and cinnamaldehyde (10-1000 microM) completely fail to interfere with the specific binding sites for the TRPV1 agonist [(3)H]-resiniferatoxin. Allyl isothiocyanate or cinnamaldehyde-mediated contractions of rat urinary bladder, which rely on external Ca(2+) influx, are significantly inhibited by tachykinin receptor antagonists as well as by tetrodotoxin (1 microM) or indomethacin (1 microM). Allyl isothiocyanate-induced contraction is not changed by atropine (1 microM) or suramin (300 microM). The exposure of urinary bladders to allyl isothiocyanate (100 microM) causes an increase in the prostaglandin E(2) and substance P levels. Taken together, these results indicate that TRPA1 agonists contract rat urinary bladder through sensory fibre stimulation, depending on extracellular Ca(2+) influx and release of tachykinins and cyclooxygenase metabolites, probably prostaglandin E(2). Thus, TRPA1 appears to exert an important role in urinary bladder function.     

Capacitative and 1-oleyl-2-acetyl-sn-glycerol-activated Ca(2+) entry distinguished using adenylyl cyclase type 8

Although the molecular identity of capacitative Ca(2+) entry (CCE) channels remains elusive, transient receptor potential channel (TRPC) family members 3, 6, and 7, which are activated by diacylglycerol (DAG), have been put forward as possible candidates. Because human embryonic kidney (HEK) 293 cells endogenously express these TRP subunits, this cell line is suitable for investigating whether DAG-activated TRP subunits form part of the putative multimeric assemblies that mediate CCE. Adenylyl cyclase type 8 (AC8) is activated by CCE in nonexcitable cells but is not responsive to other forms of Ca(2+) entry, such as ionophore- or arachidonate-activated entry through the plasma membrane. In this study, we exploited this unique dependence of AC8 on CCE to determine whether the DAG analog, 1-oleyl-2-acetyl-sn-glycerol (OAG), activates the same subset of Ca(2+) channels as store depletion, which triggers CCE. In populations of HEK 293 cells, OAG evoked a faster and greater influx of Ca(2+) than CCE. Both pathways of Ca(2+) entry could be triggered simultaneously in the same batch of cells, with additive effects. It is striking that OAG-mediated Ca(2+) entry, unlike CCE, did not stimulate AC8 activity in populations of cells. In single cells, OAG evoked a highly heterogeneous response, whereas CCE occurred as a smooth and sustained increase in [Ca(2+)](i). Taken together, our results indicate that, in HEK 293 cells, OAG-activated Ca(2+) entry is distinct from CCE. The inability of the OAG-activated Ca(2+) entry pathway to regulate AC8 further reinforces the absolute dependence of this enzyme on CCE.     

Possible involvement of transient receptor potential channels in electrophile-induced insulin secretion from RINm5F cells

Endogenously produced reactive oxygen species reportedly stimulate insulin secretion from islet β-cells. However, the molecular machinery that governs the oxidant-induced insulin secretion has yet to be determined. The present study demonstrates, using rat islet β-cell-derived RINm5F cells, the involvement of the transient receptor potential (TRP) cation channels in the insulin secretion induced by the lipid peroxidation product 4-hydroxy-2-nonenal. Short-term (1 h) exposure of 4-hydroxy-2-nonenal induced a transient increase in intracellular Ca(2+) concentration and subsequent insulin secretion in a concentration-dependent manner. The increase in intracellular Ca(2+) concentration seemed to be due to an influx through the L-type voltage-dependent Ca(2+) channel, since it was not observed when extracellular Ca(2+) was absent and was inhibited almost completely by diltiazem or nifedipine. Ruthenium red, a non-specific inhibitor of TRP channels, inhibited the Ca(2+) influx and insulin secretion evoked by 4-hydroxy-2-nonenal. Among the TRP channels, TRPA1 was found to be predominantly expressed, not only in RINm5F cells, but also rat islets. TRPA1 agonists, allylisothiocyanate and 15-deoxy-Δ(12,14)-prostaglandin J(2), significantly induced Ca(2+) influx, and a specific inhibitor TRPA1, HC-030031, blocked the effects elicited by 4-hydroxy-2-nonenal. These results suggest that 4-hydroxy-2-nonenal induces Ca(2+) influx via the activation of TRP channels, including TRPA1, which appears to be coupled with the L-type voltage-dependent Ca(2+) channel, and ultimately insulin secretion in RINm5F cells.