Transient Receptor Potential Canonical (TRPC)/Orai1-dependent Store-operated Ca2+ Channels

Abstract

Store-operated Ca2؉ entry (SOCE) has emerged as an important mechanism in cardiac pathology. However, the signals that up-regulate SOCE in the heart remain unexplored. Clinical trials have emphasized the beneficial role of mineralocorticoid receptor (MR) signaling blockade in heart failure and associated arrhythmias. Accumulated evidence suggests that the mineralocorticoid hormone aldosterone, through activation of its receptor, MR, might be a key regulator of Ca 2؉ influx in cardiomyocytes. We thus assessed whether and how SOCE involving transient receptor potential canonical (TRPC) and Orai1 channels are regulated by aldosterone/MR in neonatal rat ventricular cardiomyocytes. Molecular screening using qRT-PCR and Western blotting demonstrated that aldosterone treatment for 24 h specifically increased the mRNA and/or protein levels of Orai1, TRPC1, -C4, -C5, and stromal interaction molecule 1 through MR activation. These effects were correlated with a specific enhancement of SOCE activities sensitive to store-operated channel inhibitors (SKF-96365 and BTP2) and to a potent Orai1 blocker (S66) and were prevented by TRPC1, -C4, and Orai1 dominant negative mutants or TRPC5 siRNA. A mechanistic approach showed that up-regulation of serum-and glucocorticoid-regulated kinase 1 mRNA expression by aldosterone is involved in enhanced SOCE. Functionally, 24-h aldosterone-enhanced SOCE is associated with increased diastolic [Ca 2؉ ] i , which is blunted by store-operated channel inhibitors. Our study provides the first evidence that aldosterone promotes TRPC1-, -C4-, -C5-, and Orai1-mediated SOCE in cardiomyocytes through an MR and serum-and glucocorticoid-regulated kinase 1 pathway.The last discovered Ca 2ϩ channel family, transient receptor potential canonical (TRPC) 2 and Orai1 channels, is widely expressed, but the role of these channels and the modulation of their expression are not completely understood. Notably, the dysregulation of these important mediators of Ca 2ϩ -dependent signal transduction has been involved in a broad range of human diseases such as adenocarcinomas, type 2 diabetes and diabetic nephropathy, human proteinuric kidney disease focal and segmental glomerulosclerosis, severe immunodeficiency, congenital myopathy, chronic pulmonary disease, and ectodermal dysplasia (1, 2). Although predominantly thought of in the context of non-excitable cells, store-operated Ca 2ϩ entry (SOCE) by store-operated channels (SOCs) has recently emerged as a potential mechanism to alter Ca 2ϩ in the diseased cardiomyocyte. Although still under debate, the prime candidate proteins for SOCs encompass the TRPC channel(s) as non-selective cation channels as well as Orai1, the Ca 2ϩ selective pore-forming unit of the Ca 2ϩ release-activated Ca 2ϩ channel (3). Stromal interaction molecule 1 (STIM1) serves as a Ca 2ϩ sensor in the endoplasmic reticulum/sarcoplasmic reticulum (SR), clustering proximal to the plasma membrane to activate Orai1 (4) and TRPC channel(s) (5) when Ca 2ϩ stores are depleted. The seven isoforms of the T...

TRPC4α and TRPC4β Similarly Affect Neonatal Cardiomyocyte Survival during Chronic GPCR Stimulation

“…Due to the lack of information regarding the precise inhibitory effect of BTP2, our data only propose TRPC4 channels as down-stream targets of Ang II stimulation, but do not reveal the precise mode of channel activation. A recent study suggests that TRPC1, 4 and 5 comprise SOC channels in association with ORAI1 that are downstream targets of aldosterone stimulation in NRCs [34]. Further studies are necessary to examine whether such a miscellaneous constellation could also mediate Ca 2+ responses after Ang II stimulation.…”

Mineralocorticoid Receptor in Calcium Handling of Vascular Smooth Muscle Cells

“…Recently, we demonstrated that rat aorta treated with aldosterone (10 nM for 24 h) did not reveal changes in the expression of TRPC1, C3, C4, C5, and C6 [19]. Altogether, these studies suggest a concentration-dependent increase of TRPC channels, since we have previously demonstrated an upregulation of TRPC1, C4, and C5 in cardiomyocytes upon aldosterone concentrations higher than 100 nM [43]. Moreover, one of the features of metabolic syndrome is the elevated plasma aldosterone level [116], which has been associated with increased TRPC1 and TRPC6 expression in coronary arteries compared to lean pigs [32].…”

“…Moreover, it has been showed that the MR transcriptional activity is blunted by MR antagonists, and actinomycin D (a transcriptional inhibitor) supporting an MR-dependent effect of Aldo in vessels [16,19,30,41]. Furthermore, an increasing body of evidence has underlined the ability of MR to modulate the expression of ion channels in several vascular beds, unveiling the role of MR in vascular physiology and pathology [19,30,42,43].…”

“…Another critical component of SOCE is the protein Orai (comprising Orai1, Orai2, and Orai3), which forms a family of highly Ca 2+ -selective channels that are regulated by stromal-interacting molecules (STIM1 and STIM2) [111,112]. In neonatal cardiomyocytes, Orai1 was significantly increased by 100 nM and 1 μM aldosterone treatment, whereas lower concentrations (1 and 10 nM) had no effect [43]. However, Stim1 expression remained unchanged even at the highest concentration tested (1 μM) [43].…”

Store-operated Ca2+ entry supports contractile function in hearts of hibernators

“…Under suppressed voltage-dependent K + , Na + and Ca 2+ currents, 2-APB (40 μM) inhibited whole-cell membrane current in ground squirrel cardiomyocytes (Fig 5A). Subtraction of the currents measured in the presence of 2-APB from control records revealed a non-selective 2-APB-sensitive current component with reversal potential slightly more negative than 0 mV (E r = -11.7 ± 5.2 mV, n = 3), which is typical for non-selective SOCE measured in heterologous expression systems [59,60] or in adult cardiomyocytes [45,61]. However, in ground squirrel cardiomyocytes 2-APB-sensitive currents were detected without a pretreatment aimed at depleting intracellular Ca 2+ stores, indicating that the detected current could be induced by certain Trpc-Orai1-Stim1 channels capable of operating in store-independent mode [36,40,62].…”