Submaximal stimulation of porcine endothelial cells causes focal Ca2+ elevation beneath the cell membrane

Nanojunctions: Specificity of Ca2+ signaling requires nano-scale architecture of intracellular membrane contact sites

Spatio-temporal definition of Ca2+ signals involves the assembly of signaling complexes within the nano-architecture of contact sites between the sarco/endoplasmic reticulum (SR/ER) and the plasma membrane (PM). While the requirement of precise spatial assembly and positioning of the junctional signaling elements is well documented, the role of the nano-scale membrane architecture itself, as an ion-reflecting confinement of the signalling unit, remains as yet elusive. Utilizing the Na+/Ca2+ Exchanger-1 / SR/ER Ca2+ ATPase-2-mediated ER Ca2+ refilling process as a junctional signalling paradigm, we provide here the first evidence for an indispensable cellular function of the junctional membrane architecture. Our stochastic modeling approach demonstrates that junctional ER Ca2+ refilling operates exclusively at nano-scale membrane spacing, with a strong inverse relationship between junctional width and signaling efficiency. Our model predicts a breakdown of junctional Ca2+ signaling with loss of reflecting membrane confinement. In addition we consider interactions between Ca2+ and the phospholipid membrane surface, which may support interfacial Ca2+ transport and promote receptor targeting. Alterations in the molecular and nano-scale membrane organization at organelle-PM contacts are suggested as a new concept in pathophysiology.

Cell-To-Cell Communication in the Resistance Vasculature

The arterial vasculature can be divided into large conduit arteries, intermediate contractile arteries, resistance arteries, arterioles, and capillaries. Resistance arteries and arterioles primarily function to control systemic blood pressure. The resistance arteries are composed of a layer of endothelial cells oriented parallel to the direction of blood flow, which are separated by a matrix layer termed the internal elastic lamina from several layers of smooth muscle cells oriented perpendicular to the direction of blood flow. Cells within the vessel walls communicate in a homocellular and heterocellular fashion to govern luminal diameter, arterial resistance, and blood pressure. At rest, potassium currents govern the basal state of endothelial and smooth muscle cells. Multiple stimuli can elicit rises in intracellular calcium levels in either endothelial cells or smooth muscle cells, sourced from intracellular stores such as the endoplasmic reticulum or the extracellular space. In general, activation of endothelial cells results in the production of a vasodilatory signal, usually in the form of nitric oxide or endothelial-derived hyperpolarization. Conversely, activation of smooth muscle cells results in a vasoconstriction response through smooth muscle cell contraction. © 2022 American Physiological Society. Compr Physiol 12: 1-35, 2022.

Calcium-Dependent Ion Channels and the Regulation of Arteriolar Myogenic Tone

Arterioles in the peripheral microcirculation regulate blood flow to and within tissues and organs, control capillary blood pressure and microvascular fluid exchange, govern peripheral vascular resistance, and contribute to the regulation of blood pressure. These important microvessels display pressure-dependent myogenic tone, the steady state level of contractile activity of vascular smooth muscle cells (VSMCs) that sets resting arteriolar internal diameter such that arterioles can both dilate and constrict to meet the blood flow and pressure needs of the tissues and organs that they perfuse. This perspective will focus on the Ca²⁺-dependent ion channels in the plasma and endoplasmic reticulum membranes of arteriolar VSMCs and endothelial cells (ECs) that regulate arteriolar tone. In VSMCs, Ca²⁺-dependent negative feedback regulation of myogenic tone is mediated by Ca²⁺-activated K⁺ (BK_Ca) channels and also Ca²⁺-dependent inactivation of voltage-gated Ca²⁺ channels (VGCC). Transient receptor potential subfamily M, member 4 channels (TRPM4); Ca²⁺-activated Cl⁻ channels (CaCCs; TMEM16A/ANO1), Ca²⁺-dependent inhibition of voltage-gated K⁺ (K_V) and ATP-sensitive K⁺ (K_ATP) channels; and Ca²⁺-induced-Ca²⁺ release through inositol 1,4,5-trisphosphate receptors (IP₃Rs) participate in Ca²⁺-dependent positive-feedback regulation of myogenic tone. Calcium release from VSMC ryanodine receptors (RyRs) provide negative-feedback through Ca²⁺-spark-mediated control of BK_Ca channel activity, or positive-feedback regulation in cooperation with IP₃Rs or CaCCs. In some arterioles, VSMC RyRs are silent. In ECs, transient receptor potential vanilloid subfamily, member 4 (TRPV4) channels produce Ca²⁺ sparklets that activate IP₃Rs and intermediate and small conductance Ca²⁺ activated K⁺ (IK_Ca and sK_Ca) channels causing membrane hyperpolarization that is conducted to overlying VSMCs producing endothelium-dependent hyperpolarization and vasodilation. Endothelial IP₃Rs produce Ca²⁺ pulsars, Ca²⁺ wavelets, Ca²⁺ waves and increased global Ca²⁺ levels activating EC sK_Ca and IK_Ca channels and causing Ca²⁺-dependent production of endothelial vasodilator autacoids such as NO, prostaglandin I₂ and epoxides of arachidonic acid that mediate negative-feedback regulation of myogenic tone. Thus, Ca²⁺-dependent ion channels importantly contribute to many aspects of the regulation of myogenic tone in arterioles in the microcirculation.

RNA sequencing-based exploration of the effects of far-red light on lncRNAs involved in the shade-avoidance response of D. officinale

Dendrobium officinale (D. officinale) is a valuable medicinal plant with a low natural survival rate, and its shade-avoidance response to far-red light is as an important strategy used by the plant to improve its production efficiency. However, the lncRNAs that play roles in the shade-avoidance response of D. officinale have not yet been investigated. This study found that an appropriate proportion of far-red light can have several effects, including increasing the leaf area and accelerating stem elongation, in D. officinale. The effects of different far-red light treatments on D. officinale were analysed by RNA sequencing technology, and a total of 69 and 78 lncRNAs were differentially expressed in experimental group 1 (FR1) versus the control group (CK) (FR1-CK) and in experimental group 4 (FR4) versus the CK (FR4-CK), respectively. According to GO and KEGG analyses, most of the differentially expressed lncRNA targets are involved in the membrane, some metabolic pathways, hormone signal transduction, and O-methyltransferase activity, among other functions. Physiological and biochemical analyses showed that far-red light promoted the accumulation of flavonoids, alkaloids, carotenoids and polysaccharides in D. officinale. The effect of far-red light on D. officinalemight be closely related to the cell membrane and Ca2+ transduction. Based on a Cytoscape analysis and previous research, this study also found that MSTRG.38867.1, MSTRG.69319.1, and MSTRG.66273.1, among other components, might participate in the far-red light signalling network through their targets and thus regulate the shade-avoidance response of D. officinale. These findings will provide new insights into the shade-avoidance response of D. officinale.

Exploration of the Effect of Blue Light on Functional Metabolite Accumulation in Longan Embryonic Calli via RNA Sequencing

Light is an important factor that affects the synthesis of functional metabolites in longan embryogenic calli (ECs). However, analysis of the effect of light on functional metabolites in longan ECs via RNA sequencing has rarely been reported and their light regulation network is unclear. The contents of various functional metabolites as well as the enzymatic activities of superoxide dismutase and peroxidase and the level of H₂O₂ in longan ECs were significantly higher under blue light treatment than under the other treatments (dark, white). In this study, we sequenced three mRNA libraries constructed from longan ECs subjected to different treatments. A total of 4463, 1639 and 1806 genes were differentially expressed in the dark versus blue (DB), dark versus white (DW) and white versus blue (WB) combinations, respectively. According to GO and KEGG analyses, most of the differentially expressed genes (DEGs) identified were involved in transmembrane transport, taurine and hypotaurine metabolism, calcium transport and so forth. Mapman analysis revealed that more DEGs were identified in each DB combination pathway than in DW combination pathways, indicating that blue light exerts a significantly stronger regulatory effect on longan EC metabolism than the other treatments. Based on previous research and transcriptome data mining, a blue light signaling network of genes that affect longan functional metabolites was constructed and HY5, PIF4 and MYC2 were shown to be the key regulatory genes in the network. The results of this study demonstrate that the expression levels of phase-specific genes vary with changes in longan EC functional metabolites.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Critical contribution of Na+-Ca2+ exchanger to the Ca2+-mediated vasodilation activated in endothelial cells of resistance arteries

Na⁺-Ca²⁺ exchanger (NCX) contributes to control the intracellular free Ca²⁺ concentration ([Ca²⁺]_i), but the functional activation of NCX reverse mode (NCXrm) in endothelial cells is controversial. We evaluated the participation of NCXrm-mediated Ca²⁺ uptake in the endothelium-dependent vasodilation of rat isolated mesenteric arterial beds. In phenylephrine-contracted mesenteries, the acetylcholine (ACh)-induced vasodilation was abolished by treatment with the NCXrm blockers SEA0400, KB-R7943, or SN-6. Consistent with that, the ACh-induced hyperpolarization observed in primary cultures of mesenteric endothelial cells and in smooth muscle of isolated mesenteric resistance arteries was attenuated by KB-R7943 and SEA0400, respectively. In addition, both blockers abolished the NO production activated by ACh in intact mesenteric arteries. In contrast, the inhibition of NCXrm did not affect the vasodilator responses induced by the Ca²⁺ ionophore, ionomycin, and the NO donor, S-nitroso- N-acetylpenicillamine. Furthermore, SEA0400, KB-R7943, and a small interference RNA directed against NCX1 blunted the increase in [Ca²⁺]_i induced by ACh or ATP in cultured endothelial cells. The analysis by proximity ligation assay showed that the NO-synthesizing enzyme, eNOS, and NCX1 were associated in endothelial cell caveolae of intact mesenteric resistance arteries. These results indicate that the activation of NCXrm has a central role in Ca²⁺-mediated vasodilation initiated by ACh in endothelial cells of resistance arteries.-Lillo, M. A., Gaete, P. S., Puebla, M., Ardiles, N. M., Poblete, I., Becerra, A., Simon, F., Figueroa, X. F. Critical contribution of Na⁺-Ca²⁺ exchanger to the Ca²⁺-mediated vasodilation activated in endothelial cells of resistance arteries.

IP3 receptor signaling and endothelial barrier function

The endothelium, a monolayer of endothelial cells lining vessel walls, maintains tissue-fluid homeostasis by restricting the passage of the plasma proteins and blood cells into the interstitium. The ion Ca²⁺, a ubiquitous secondary messenger, initiates signal transduction events in endothelial cells that is critical to control of vascular tone and endothelial permeability. The ion Ca²⁺ is stored inside the intracellular organelles and released into the cytosol in response to environmental cues. The inositol 1,4,5-trisphosphate (IP₃) messenger facilitates Ca²⁺ release through IP₃ receptors which are Ca²⁺-selective intracellular channels located within the membrane of the endoplasmic reticulum. Binding of IP₃ to the IP₃Rs initiates assembly of IP₃R clusters, a key event responsible for amplification of Ca²⁺ signals in endothelial cells. This review discusses emerging concepts related to architecture and dynamics of IP₃R clusters, and their specific role in propagation of Ca²⁺ signals in endothelial cells.

Na +/Ca2+ exchangers and Orai channels jointly refill endoplasmic reticulum (ER) Ca2+ via ER nanojunctions in vascular endothelial cells

We investigated the role of Na⁺/ Ca²⁺ exchange (NCX) in the refilling of endoplasmic reticulum (ER) Ca²⁺ in vascular endothelial cells under various conditions of cell stimulation and plasma membrane (PM) polarization. Better understanding of the mechanisms behind basic ER Ca²⁺ content regulation is important, since current hypotheses on the possible ultimate causes of ER stress point to deterioration of the Ca²⁺ transport mechanism to/from ER itself. We measured [Ca²⁺]_i temporal changes by Fura-2 fluorescence under experimental protocols that inhibit a host of transporters (NCX, Orai, non-selective transient receptor potential canonical (TRPC) channels, sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA), Na⁺/ K⁺ ATPase (NKA)) involved in the Ca²⁺ communication between the extracellular space and the ER. Following histamine-stimulated ER Ca²⁺ release, blockade of NCX Ca²⁺-influx mode (by 10 μM KB-R7943) diminished the ER refilling capacity by about 40%, while in Orai1 dominant negative-transfected cells NCX blockade attenuated ER refilling by about 60%. Conversely, inhibiting the ouabain sensitive NKA (10 nM ouabain), which may be localized in PM-ER junctions, increased the ER Ca²⁺ releasable fraction by about 20%, thereby supporting the hypothesis that this process of privileged ER refilling is junction-mediated. Junctions were observed in the cell ultrastructure and their main parameters of membrane separation and linear extension were (9.6 ± 3.8) nm and (128 ± 63) nm, respectively. Our findings point to a process of privileged refilling of the ER, in which NCX and store-operated Ca²⁺ entry via the stromal interaction molecule (STIM)-Orai system are the sole protagonists. These results shed light on the molecular machinery involved in the function of a previously hypothesized subplasmalemmal Ca²⁺ control unit during ER refilling with extracellular Ca²⁺.

GPR55 agonist lysophosphatidylinositol and lysophosphatidylcholine inhibit endothelial cell hyperpolarization via GPR-independent suppression of Na+-Ca2+ exchanger and endoplasmic reticulum Ca2+ refilling

Lysophosphatidylinositol (LPI) and lysophosphatidylcholine (LPC) are lipid signaling molecules that induce endothelium-dependent vasodilation. In addition, LPC suppresses acetylcholine (Ach)-induced responses. We aimed to determine the influence of LPC and LPI on hyperpolarizing responses in vitro and in situ endothelial cells (EC) and identify the underlying mechanisms. Using patch-clamp method, we show that LPI and LPC inhibit EC hyperpolarization to histamine and suppress Na⁺/Ca²⁺ exchanged (NCX) currents in a concentration-dependent manner. The inhibition is non-mode-specific and unaffected by intracellular GDPβS infusion and tempol, a superoxide dismutase mimetic. In excised mouse aorta, LPI strongly inhibits the sustained and the peak endothelial hyperpolarization induced by Ach, but not by SKA-31, an opener of Ca²⁺-dependent K⁺ channels of intermediate and small conductance. The hyperpolarizing responses to consecutive histamine applications are strongly reduced by NCX inhibition. In a Ca²⁺-re-addition protocol, bepridil, a NCX inhibitor, and KB-R7943, a blocker of reversed NCX, inhibit the hyperpolarizing responses to Ca²⁺-re-addition following Ca²⁺ stores depletion. These finding indicate that LPC and LPI inhibit endothelial hyperpolarization to Ach and histamine independently of G-protein coupled receptors and superoxide anions. Reversed NCX is critical for ER Ca²⁺ refilling in EC. The inhibition of NCX by LPI and LPC underlies diminished endothelium-dependent responses and endothelial dysfunction accompanied by increased levels of these lipids in the blood.

Functional impairment of endothelial cells by the antimycotic amphotericin B

We set out to determine the membrane potential (Vm) of the endothelial cell line EA.hy926 and its sensitivity to the antimycotic amphotericin B (AmB), a commonly used antifungal component in cell culture media. We measured the endothelial Vm under various experimental conditions by patch clamp technique and found that Vm of AmB-treated cells is (-12.1 ± 9.3) mV, while in AmB-untreated (control) cells it is (-57.1 ± 4.1) mV. In AmB-free extracellular solutions, Vm recovered toward control levels and this gain in Vm rapidly dissipated upon re-addition of AmB, demonstrating a rapid and reversible effect of AmB on endothelial Vm. The consequences of AmB dependent alterations in endothelial transmembrane potential were tested at the levels of Ca(2+) signaling, of nucleotide concentrations, and energy metabolism. In AmB-treated cells we found substantially reduced Ca(2+) entry (to about 60% of that in control cells) in response to histamine induced endoplasmic reticulum (ER) Ca(2+) depletion, and diminished the ATP-to-ADP ratio (by >30%). Our data demonstrate a marked and experimentally relevant dependence of basic functional parameters of cultured endothelial cells on the presence of the ionophoric antimycotic AmB. The profound and reversible effects of the widely used culture media component AmB need careful consideration when interpreting experimental data obtained under respective culture conditions.

Microtubule-Associated Protein EB3 Regulates IP3 Receptor Clustering and Ca(2+) Signaling in Endothelial Cells

The mechanisms by which the microtubule cytoskeleton regulates the permeability of endothelial barrier are not well understood. Here, we demonstrate that microtubule-associated end-binding protein 3 (EB3), a core component of the microtubule plus-end protein complex, binds to inositol 1,4,5-trisphosphate receptors (IP3Rs) through an S/TxIP EB-binding motif. In endothelial cells, α-thrombin, a pro-inflammatory mediator that stimulates phospholipase Cβ, increases the cytosolic Ca(2+) concentration and elicits clustering of IP3R3s. These responses, and the resulting Ca(2+)-dependent phosphorylation of myosin light chain, are prevented by depletion of either EB3 or mutation of the TxIP motif of IP3R3 responsible for mediating its binding to EB3. We also show that selective EB3 gene deletion in endothelial cells of mice abrogates α-thrombin-induced increase in endothelial permeability. We conclude that the EB3-mediated interaction of IP3Rs with microtubules controls the assembly of IP3Rs into effective Ca(2+) signaling clusters, which thereby regulate microtubule-dependent endothelial permeability.

The endocannabinoid N-arachidonoyl glycine (NAGly) inhibits store-operated Ca2+ entry by preventing STIM1-Orai1 interaction

The endocannabiniod anandamide (AEA) and its derivate N-arachidonoyl glycine (NAGly) have a broad spectrum of physiological effects, which are induced by both binding to receptors and receptor-independent modulations of ion channels and transporters. The impact of AEA and NAGly on store-operated Ca(2+) entry (SOCE), a ubiquitous Ca(2+) entry pathway regulating many cellular functions, is unknown. Here we show that NAGly, but not AEA reversibly hinders SOCE in a time- and concentration-dependent manner. The inhibitory effect of NAGly on SOCE was found in the human endothelial cell line EA.hy926, the rat pancreatic β-cell line INS-1 832/13, and the rat basophilic leukemia cell line RBL-2H3. NAGly diminished SOCE independently from the mode of Ca(2+) depletion of the endoplasmic reticulum, whereas it had no effect on Ca(2+) entry through L-type voltage-gated Ca(2+) channels. Enhanced Ca(2+) entry was effectively hampered by NAGly in cells overexpressing the key molecular constituents of SOCE, stromal interacting molecule 1 (STIM1) and the pore-forming subunit of SOCE channels, Orai1. Fluorescence microscopy revealed that NAGly did not affect STIM1 oligomerization, STIM1 clustering, or the colocalization of STIM1 with Orai1, which were induced by Ca(2+) depletion of the endoplasmic reticulum. In contrast, independently from its slow depolarizing effect on mitochondria, NAGly instantly and strongly diminished the interaction of STIM1 with Orai1, indicating that NAGly inhibits SOCE primarily by uncoupling STIM1 from Orai1. In summary, our findings revealed the STIM1-Orai1-mediated SOCE machinery as a molecular target of NAGly, which might have many implications in cell physiology.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Leucine zipper EF hand-containing transmembrane protein 1 (Letm1) and uncoupling proteins 2 and 3 (UCP2/3) contribute to two distinct mitochondrial Ca2+ uptake pathways

Cytosolic Ca²⁺ signals are transferred into mitochondria over a huge concentration range. In our recent work we described uncoupling proteins 2 and 3 (UCP2/3) to be fundamental for mitochondrial uptake of high Ca²⁺ domains in mitochondria-ER junctions. On the other hand, the leucine zipper EF hand-containing transmembrane protein 1 (Letm1) was identified as a mitochondrial Ca²⁺/H⁺ antiporter that achieved mitochondrial Ca²⁺ sequestration at small Ca²⁺ increases. Thus, the contributions of Letm1 and UCP2/3 to mitochondrial Ca²⁺ uptake were compared in endothelial cells. Knock-down of Letm1 did not affect the UCP2/3-dependent mitochondrial uptake of intracellularly released Ca²⁺ but strongly diminished the transfer of entering Ca²⁺ into mitochondria, subsequently, resulting in a reduction of store-operated Ca²⁺ entry (SOCE). Knock-down of Letm1 and UCP2/3 did neither impact on cellular ATP levels nor the membrane potential. The enhanced mitochondrial Ca²⁺ signals in cells overexpressing UCP2/3 rescued SOCE upon Letm1 knock-down. In digitonin-permeabilized cells, Letm1 exclusively contributed to mitochondrial Ca²⁺ uptake at low Ca²⁺ conditions. Neither the Letm1- nor the UCP2/3-dependent mitochondrial Ca²⁺ uptake was affected by a knock-down of mRNA levels of mitochondrial calcium uptake 1 (MICU1), a protein that triggers mitochondrial Ca²⁺ uptake in HeLa cells. Our data indicate that Letm1 and UCP2/3 independently contribute to two distinct, mitochondrial Ca²⁺ uptake pathways in intact endothelial cells.

Mitochondrial Ca2+ uptake and not mitochondrial motility is required for STIM1-Orai1-dependent store-operated Ca2+ entry

Store-operated Ca2+ entry (SOCE) is established by formation of subplasmalemmal clusters of the endoplasmic reticulum (ER) protein, stromal interacting molecule 1 (STIM1) upon ER Ca2+ depletion. Thereby, STIM1 couples to plasma membrane channels such as Orai1. Thus, a close proximity of ER domains to the plasma membrane is a prerequisite for SOCE activation, challenging the concept of local Ca2+ buffering by mitochondria as being essential for SOCE. This study assesses the impact of mitochondrial Ca2+ handling and motility on STIM1–Orai1-dependent SOCE. High-resolution microscopy showed only 10% of subplasmalemmal STIM1 clusters to be colocalized with mitochondria. Impairments of mitochondrial Ca2+ handling by inhibition of mitochondrial Na+-Ca2+ exchanger (NCXmito) or depolarization only partially suppressed Ca2+ entry in cells overexpressing STIM1-Orai1. However, SOCE was completely abolished when both NCXmito was inhibited and the inner mitochondrial membrane was depolarized, in STIM1- and Orai1-overexpressing cells. Immobilization of mitochondria by expression of mAKAP-RFP-CAAX, a construct that physically links mitochondria to the plasma membrane, affected the Ca2+ handling of the organelles but not the activity of SOCE. Our observations indicate that mitochondrial Ca2+ uptake, including reversal of NCXmito, is fundamental for STIM1–Orai1-dependent SOCE, whereas the proximity of mitochondria to STIM1-Orai1 SOCE units and their motility is not required.

Effect of l-Arginine Analogs and a Calcium Chelator on Nitric Oxide (NO˙) Production byLeishmaniasp

Leishmania amazonensis, L. braziliensis and L. chagasi promastigotes were grown in the presence of L-arginine analogs such as Nomega-nitro-L-arginine methyl ester (L-NAME), NG-nitro-L-arginine (L-NNA) and D-arginine (an inactive L-arginine isomer), besides an intracellular calcium chelator [ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetra acetic acid; EGTA] to verify the importance of L-arginine metabolism and the cofactors for these parasites. The parasite's growth curve was followed up and the culture supernatants were used to assay nitric oxide (NO) production by the Griess reaction. The results showed a significant effect of L-arginine analogs on NO production by all Leishmania species studied, especially L-NAME, an irreversible inhibitor of the constitutive nitric oxide synthase (cNOS). When L. amazonensis promastigotes were pre-incubated with L-NAME, the infection range of the murine macrophages was lowered to 61% in 24 h and 19% after 48 h. These data demonstrated that the parasite NO pathway is important to the establishment of the infection.

Cytosolic Ca2+ prevents the subplasmalemmal clustering of STIM1: an intrinsic mechanism to avoid Ca2+ overload

The stromal interacting molecule (STIM1) is pivotal for store-operated Ca(2+) entry (SOC). STIM1 proteins sense the Ca(2+) concentration within the lumen of the endoplasmic reticulum (ER) via an EF-hand domain. Dissociation of Ca(2+) from this domain allows fast oligomerization of STIM1 and the formation of spatially discrete clusters close to the plasma membrane. By lifetime-imaging of STIM1 interaction, the rearrangement of STIM1, ER Ca(2+) concentration ([Ca(2+)](ER)) and cytosolic Ca(2+) signals ([Ca(2+)](cyto)) we show that [Ca(2+)](cyto) affects the subcellular distribution of STIM1 oligomers and prevents subplasmalemmal STIM clustering, even if the ER is depleted. These data indicate that [Ca(2+)](cyto), independently of the ER Ca(2+) filling state, crucially tunes the formation and disassembly of subplasmalemmal STIM1 clusters, and, thus, protects cells against Ca(2+) overload resulting from excessive SOC activity.

Impaired capsaicin-induced relaxation of coronary arteries in a porcine model of the metabolic syndrome

Recent studies implicate channels of the transient receptor potential vanilloid family (e.g., TRPV1) in regulating vascular tone; however, little is known about these channels in the coronary circulation. Furthermore, it is unclear whether metabolic syndrome alters the function and/or expression of TRPV1. We tested the hypothesis that TRPV1 mediates coronary vasodilation through endothelium-dependent mechanisms that are impaired by the metabolic syndrome. Studies were conducted on coronary arteries from lean and obese male Ossabaw miniature swine. In lean pigs, capsaicin, a TRPV1 agonist, relaxed arteries in a dose-dependent manner (EC50 = 116 +/- 41 nM). Capsaicin-induced relaxation was blocked by the TRPV1 antagonist capsazepine, endothelial denudation, inhibition of nitric oxide synthase, and K+ channel antagonists. Capsaicin-induced relaxation was impaired in rings from pigs with metabolic syndrome (91 +/- 4% vs. 51 +/- 10% relaxation at 100 microM). TRPV1 immunoreactivity was prominent in coronary endothelial cells. TRPV1 protein expression was decreased 40 +/- 11% in obese pigs. Capsaicin (100 microM) elicited divalent cation influx that was abolished in endothelial cells from obese pigs. These data indicate that TRPV1 channels are functionally expressed in the coronary circulation and mediate endothelium-dependent vasodilation through a mechanism involving nitric oxide and K+ channels. Impaired capsaicin-induced vasodilation in the metabolic syndrome is associated with decreased expression of TRPV1 and cation influx.

Estrogen and the Ca2+-mobilizing agonist ATP evoke acute NO synthesis via distinct pathways in an individual human vascular endothelium-derived cell

In this study, we have systematically evaluated the signaling mechanisms underlying stimulated nitric oxide (NO) synthesis by estrogen (E2) and other vasoactive agents at the level of a single endothelium-derived cell. To do so, we have characterized and contrasted rapid E2-evoked NO synthesis with that of ATP using single-cell microfluorimetry and patch-clamp recordings to monitor stimulated changes in cellular NO synthesis (via 4-amino-5-methylamino-2',7'-difluorofluorescein), Ca2+ transients (via Fluo-3), and membrane hyperpolarization in cultured human EA.hy926 cells. E2-evoked NO synthesis in single cells (EC50 approximately 0.3 nM) was blocked by the E2 receptor antagonist ICI 182,780 and the NO synthase inhibitor N(omega)-nitro-l-arginine methyl ester. Although both E2 and ATP stimulated comparable Ca2+ transients, E2-induced NO synthesis was insensitive to intracellular BAPTA-AM or removal of external Ca2+. In contrast, ATP-evoked NO production was abolished by either one of these treatments. ATP-evoked hyperpolarizations ( approximately 20 mV) and NO production were both inhibited by the respective small-conductance and intermediate-conductance calcium- activated K+ channel blockers apamin and charybdotoxin. E2 minimally affected membrane potential, and stimulated NO synthesis was insensitive to calcium-activated K+ channel blockers. Exposure to either the phosphatidylinositol 3-kinase inhibitor LY-294002 or the MAP kinase inhibitor PD-98059 abolished the NO response to E2, but not that to ATP. Finally, the NO response evoked by a combined stimulus of E2 plus ATP was similar to that of ATP alone. In conclusion, our data directly demonstrate that an individual human EA.hy926 cell contains at least two distinct mechanisms for stimulated NO synthesis that depend on either calcium or protein kinase signaling events.

Role of the microtubule cytoskeleton in the function of the store-operated Ca2+ channel activator STIM1

We examined the role of the microtubule cytoskeleton in the localization and store-operated Ca(2+) entry (SOCE) function of the endoplasmic reticulum (ER) Ca(2+) sensor stromal interaction molecule 1 (STIM1) in HEK 293 cells. STIM1 tagged with an enhanced yellow fluorescent protein (EYFP-STIM1) exhibited a fibrillar localization that colocalized with endogenous alpha-tubulin. Depolymerization of microtubules with nocodazole caused a change from a fibrillar EYFP-STIM1 localization to one that was similar to that of the ER. Treatment of HEK 293 cells with nocodazole had a detrimental impact on SOCE and the associated Ca(2+) release-activated Ca(2+) current (I(CRAC)). This inhibition was significantly reversed in cells overexpressing EYFP-STIM1, implying that the primary inhibitory effect of nocodazole is related to STIM1 function. Surprisingly, nocodazole treatment alone induced significant SOCE and I(CRAC) in cells expressing EYFP-STIM1, and this was accompanied by an increase in EYFP-STIM1 fluorescence near the plasma membrane. We conclude that microtubules play a facilitative role in the SOCE signaling pathway by optimizing the localization of STIM1.

Mitochondria and Ca(2+) signaling: old guests, new functions

Mitochondria are ancient endosymbiotic guests that joined the cells in the evolution of complex life. While the unique ability of mitochondria to produce adenosine triphosphate (ATP) and their contribution to cellular nutrition metabolism received condign attention, our understanding of the organelle's contribution to Ca(2+) homeostasis was restricted to serve as passive Ca(2+) sinks that accumulate Ca(2+) along the organelle's negative membrane potential. This paradigm has changed radically. Nowadays, mitochondria are known to respond to environmental Ca(2+) and to contribute actively to the regulation of spatial and temporal patterns of intracellular Ca(2+) signaling. Accordingly, mitochondria contribute to many signal transduction pathways and are actively involved in the maintenance of capacitative Ca(2+) entry, the accomplishment of Ca(2+) refilling of the endoplasmic reticulum and Ca(2+)-dependent protein folding. Mitochondrial Ca(2+) homeostasis is complex and regulated by numerous, so far, genetically unidentified Ca(2+) channels, pumps and exchangers that concertedly accomplish the organelle's Ca(2+) demand. Notably, mitochondrial Ca(2+) homeostasis and functions are crucially influenced by the organelle's structural organization and motility that, in turn, is controlled by matrix/cytosolic Ca(2+). This review intends to provide a condensed overview on the molecular mechanisms of mitochondrial Ca(2+) homeostasis (uptake, buffering and storage, extrusion), its modulation by other ions, kinases and small molecules, and its contribution to cellular processes as fundamental basis for the organelle's contribution to signaling pathways. Hence, emphasis is given to the structure-to-function and mobility-to-function relationship of the mitochondria and, thereby, bridging our most recent knowledge on mitochondria with the best-established mitochondrial function: metabolism and ATP production.

Endothelial mitochondria: contributing to vascular function and disease

Disturbances in vascular function contribute to the development of several diseases of increasing prevalence and thereby contribute significantly to human mortality and morbidity. Atherosclerosis, diabetes, heart failure, and ischemia with attendant reperfusion injury share many of the same risk factors, among the most important being oxidative stress and alterations in the blood concentrations of compounds that influence oxidative stress, such as oxidized low-density lipoprotein. In this review, we focus on endothelial cells: cells in the frontline against these disturbances. Because ATP supplies in endothelial cells are relatively independent of mitochondrial oxidative pathways, the mitochondria of endothelial cells have been somewhat neglected. However, they are emerging as agents with diverse roles in modulating the dynamics of intracellular calcium and the generation of reactive oxygen species and nitric oxide. The mitochondria may also constitute critical "targets" of oxidative stress, because survival of endothelial cells can be compromised by opening of the mitochondrial permeability transition pore or by mitochondrial pathways of apoptosis. In addition, evidence suggests that endothelial mitochondria may play a "reconnaissance" role. For example, although the exact mechanism remains obscure, endothelial mitochondria may sense levels of oxygen in the blood and relay this information to cardiac myocytes as well as modulating the vasodilatory response mediated by endothelial nitric oxide.

Ca2+-pumps and Na2+-Ca2+-exchangers in coronary artery endothelium versus smooth muscle

Vascular endothelial cells (EC) and smooth muscle cells (SMC) require a decrease in cytoplasmic Ca²⁺ concentration after activation. This can be achieved by Ca²⁺ sequestration by the sarco-/endoplasmic reticulum Ca²⁺ pumps (SERCA) and Ca²⁺ extrusion by plasma membrane Ca²⁺ pumps (PMCA) and Na⁺–Ca²⁺-exchangers (NCX). Since the two cell types differ in their structure and function, we compared the activities of PMCA, NCX and SERCA in pig coronary artery EC and SMC, the types of isoforms expressed using RT-PCR, and their protein abundance using Western blots. The activity of NCX is higher in EC than in SMC but those of PMCA and SERCA is lower. Consistently, the protein abundance for NCX protein is higher in EC than in SMC and those of PMCA and SERCA is lower. Based on RT-PCR experiments, the types of RNA present are as follows: EC for PMCA1 while SMC for PMCA4 and PMCA1; EC for SERCA2 and SERCA3 and SMC for SERCA2. Both EC and SMC express NCX1 (mainly NCX1.3). PMCA, SERCA and NCX differ in their affinities for Ca²⁺ and regulation. Based on these observations and the literature, we conclude that the tightly regulated Ca²⁺ removal systems in SMC are consistent with the cyclical control of contractility of the filaments and those in EC are consistent with Ca²⁺ regulation of the endothelial nitric oxide synthase near the cell surface. The differences between EC and SMC should be considered in therapeutic interventions of cardiovascular diseases.

Deficiency in parvalbumin, but not in calbindin D-28k upregulates mitochondrial volume and decreases smooth endoplasmic reticulum surface selectively in a peripheral, subplasmalemmal region in the soma of Purkinje cells

The Ca(2+)-binding proteins parvalbumin (PV) and calbindin D-28k (CB) are key players in the intracellular Ca(2+)-buffering in specific cells including neurons and have profound effects on spatiotemporal aspects of Ca(2+) transients. The previously observed increase in mitochondrial volume density in fast-twitch muscle of PV-/- mice is viewed as a specific compensation mechanism to maintain Ca(2+) homeostasis. Since cerebellar Purkinje cells (PC) are characterized by high expression levels of the Ca(2+) buffers PV and CB, the question was raised, whether homeostatic mechanisms are induced in PC lacking these buffers. Mitochondrial volume density, i.e. relative mitochondrial mass was increased by 40% in the soma of PV-/- PC. Upregulation of mitochondrial volume density was not homogenous throughout the soma, but was selectively restricted to a peripheral region of 1.5 microm width underneath the plasma membrane. Accompanied was a decreased surface of subplasmalemmal smooth endoplasmic reticulum (sPL-sER) in a shell of 0.5 microm thickness underneath the plasma membrane. These alterations were specific for the absence of the "slow-onset" buffer PV, since in CB-/- mice neither changes in peripheral mitochondria nor in sPL-sER were observed. This implicates that the morphological alterations are aimed to specifically substitute the function of the slow buffer PV. We propose a novel concept that homeostatic mechanisms of components involved in Ca(2+) homeostasis do not always occur at the level of similar or closely related molecules. Rather the cell attempts to restore spatiotemporal aspects of Ca(2+) signals prevailing in the undisturbed (wildtype) situation by subtly fine tuning existing components involved in the regulation of Ca(2+) fluxes.

Ca2+ refilling of the endoplasmic reticulum is largely preserved albeit reduced Ca2+ entry in endothelial cells

In this study the relationship between the efficiency of endoplasmic reticulum (ER) Ca2+ refilling and the extent of Ca2+ entry was investigated in endothelial cells. ER and mitochondrial Ca2+ concentration were measured using genetically encoded Ca2+ sensors, while the amount of entering Ca2+ was controlled by varying either the extracellular Ca2+ or the electrical driving force for Ca2+ by changing the plasma membrane potential. In the absence of an agonist, ER Ca2+ replenishment was fully accomplished even if the Ca2+ concentration applied was reduced from 2 to 0.5mM. A similar strong efficiency of ER Ca2+ refilling was obtained under condition of plasma membrane depolarization. However, in the presence of histamine, ER Ca2+ refilling depended on mitochondrial Ca2+ transport and was more susceptible to membrane depolarization. Store-operated Ca2+ entry (SOCE), was strongly reduced under low Ca2+ and depolarizing conditions but increased if ER Ca2+ uptake was blocked or if ER Ca2+ was released continuously by IP(3). A correlation of the kinetics of ER Ca2+refilling with cytosolic Ca2+ signals revealed that termination of SOCE is a rapid event that is not delayed compared to ER refilling. Our data indicate that ER refilling occurs in priority to, and independently from the cytosolic Ca2+ elevation upon Ca2+ entry and that this important process is widely achieved even under conditions of diminished Ca2+entry.

Mitochondria maintain maturation and secretion of lipoprotein lipase in the endoplasmic reticulum

Considering the physiological Ca2+ dynamics within the ER (endoplasmic reticulum), it remains unclear how efficient protein folding is maintained in living cells. Thus, utilizing the strictly folding-dependent activity and secretion of LPL (lipoprotein lipase), we evaluated the impact of ER Ca2+ content and mitochondrial contribution to Ca2+-dependent protein folding. Exhaustive ER Ca2+ depletion by inhibition of sarcoplasmic/endoplasmic reticulum Ca2+-ATPases caused strong, but reversible, reduction of cell-associated and released activity of constitutive and adenovirus-encoded human LPL in CHO-K1 (Chinese-hamster ovary K1) and endothelial cells respectively, which was not due to decline of mRNA or intracellular protein levels. In contrast, stimulation with the IP3 (inositol 1,4,5-trisphosphate)-generating agonist histamine only moderately and transiently affected LPL maturation in endothelial cells that paralleled a basically preserved ER Ca2+ content. However, in the absence of extracellular Ca2+ or upon prevention of transmitochondrial Ca2+ flux, LPL maturation discontinued upon histamine stimulation. Collectively, these data indicate that Ca2+-dependent protein folding in the ER is predominantly controlled by intraluminal Ca2+ and is largely maintained during physiological cell stimulation owing to efficient ER Ca2+ refilling. Since Ca2+ entry and mitochondrial Ca2+ homoeostasis are crucial for continuous Ca2+-dependent protein maturation in the ER, their pathological alterations may result in dysfunctional protein folding.

LPL-mediated lipolysis of VLDL induces an upregulation of AU-rich mRNAs and an activation of HuR in endothelial cells

Lipoprotein lipase (LPL), the major enzyme for hydrolysis of circulating triglyceride-rich lipoproteins, is bound to the luminal surface of capillary endothelial cells. Products of LPL-mediated lipolysis, such as free fatty acids (FFA) and lipoprotein-remnants, can affect endothelial function and gene expression, and hence vascular homeostasis. In this study we tried to identify lipolysis-induced mRNAs in porcine aortic endothelial cells (ECAP) using a cDNA subtraction method. cDNA obtained from ECAP incubated with LPL and VLDL was subtracted from cDNA from cells cultured under control conditions. Analysis of the identified sequences revealed an upregulation of several mRNAs with adenine and uracil-rich elements (ARE) in their 3'-untranslated regions, such as IL-8, ESM-1 and VCAM-1. HuR, a ubiquitously expressed RNA-binding protein, is known to stabilize ARE-harboring mRNAs. Therefore, we investigated whether HuR is involved in this process and found that lipolysis induced an increased polysomal localization of HuR, which is typical for its activation pathway. In addition, the mRNAs for GM-CSF and TNF-alpha - established ARE-containing targets for HuR-mediated regulation - were upregulated by LPL-mediated lipolysis in ECAP. Differential expression of AU-rich mRNAs in response to LPL-mediated lipolysis might have an impact on physiological processes regulating lipid metabolism or pathophysiological processes promoting endothelial dysfunction and atherogenesis.

Na+-K+ pump activation inhibits endothelium-dependent relaxation by activating the forward mode of Na+/Ca2+ exchanger in mouse aorta

The effect of Na+-K+ pump activation on endothelium-dependent relaxation (EDR) and on intracellular Ca2+ concentration ([Ca2+]i) was examined in mouse aorta and mouse aortic endothelial cells (MAECs). The Na+-K+ pump was activated by increasing extracellular K+ concentration ([K+]o) from 6 to 12 mM. In aortic rings, the Na+ ionophore monensin evoked EDR, and this EDR was inhibited by the Na+/Ca2+ exchanger (NCX; reverse mode) inhibitor KB-R7943. Monensin-induced Na+ loading or extracellular Na+ depletion (Na+ replaced by Li+) increased [Ca2+]i in MAECs, and this increase was inhibited by KB-R7943. Na+-K+ pump activation inhibited EDR and [Ca2+]i increase (K+-induced inhibition of EDR and [Ca2+]i increase). The Na+-K+ pump inhibitor ouabain inhibited K+-induced inhibition of EDR. Monensin (>0.1 microM) and the NCX (forward and reverse mode) inhibitors 2'4'-dichlorobenzamil (>10 microM) or Ni2+ (>100 microM) inhibited K+-induced inhibition of EDR and [Ca2+]i increase. KB-R7943 did not inhibit K+-induced inhibition at up to 10 microM but did at 30 microM. In current-clamped MAECs, an increase in [K+]o from 6 to 12 mM depolarized the membrane potential, which was inhibited by ouabain, Ni2+, or KB-R7943. In aortic rings, the concentration of cGMP was significantly increased by acetylcholine and decreased on increasing [K+]o from 6 to 12 mM. This decrease in cGMP was significantly inhibited by pretreating with ouabain (100 microM), Ni2+ (300 microM), or KB-R7943 (30 microM). These results suggest that activation of the forward mode of NCX after Na+-K+ pump activation inhibits Ca2+ mobilization in endothelial cells, thereby modulating vasomotor tone.

Store-Operated Calcium Channels

In electrically nonexcitable cells, Ca2+influx is essential for regulating a host of kinetically distinct processes involving exocytosis, enzyme control, gene regulation, cell growth and proliferation, and apoptosis. The major Ca2+entry pathway in these cells is the store-operated one, in which the emptying of intracellular Ca2+stores activates Ca2+influx (store-operated Ca2+entry, or capacitative Ca2+entry). Several biophysically distinct store-operated currents have been reported, but the best characterized is the Ca2+release-activated Ca2+current, ICRAC. Although it was initially considered to function only in nonexcitable cells, growing evidence now points towards a central role for ICRAC-like currents in excitable cells too. In spite of intense research, the signal that relays the store Ca2+content to CRAC channels in the plasma membrane, as well as the molecular identity of the Ca2+sensor within the stores, remains elusive. Resolution of these issues would be greatly helped by the identification of the CRAC channel gene. In some systems, evidence suggests that store-operated channels might be related to TRP homologs, although no consensus has yet been reached. Better understood are mechanisms that inactivate store-operated entry and hence control the overall duration of Ca2+entry. Recent work has revealed a central role for mitochondria in the regulation of ICRAC, and this is particularly prominent under physiological conditions. ICRACtherefore represents a dynamic interplay between endoplasmic reticulum, mitochondria, and plasma membrane. In this review, we describe the key electrophysiological features of ICRACand other store-operated Ca2+currents and how they are regulated, and we consider recent advances that have shed insight into the molecular mechanisms involved in this ubiquitous and vital Ca2+entry pathway.

Visualization of localized store-operated calcium entry in mouse astrocytes. Close proximity to the endoplasmic reticulum

Unloading of endoplasmic reticulum (ER) Ca(2+) stores activates influx of extracellular Ca(2+) through 'store-operated' Ca(2+) channels (SOCs) in the plasma membrane (PM) of most cells, including astrocytes. A key unresolved issue concerning SOC function is their spatial relationship to ER Ca(2+) stores. Here, using high resolution imaging with the membrane-associated Ca(2+) indicator, FFP-18, it is shown that store-operated Ca(2+) entry (SOCE) in primary cultured mouse cortical astrocytes occurs at plasma membrane-ER junctions. In the absence of extracellular Ca(2+), depletion of ER Ca(2+) stores using cyclopiazonic acid, an ER Ca(2+)-ATPase inhibitor, and caffeine transiently increases the sub-plasma-membrane Ca(2+) concentration ([Ca(2+)](SPM)) within a restricted space between the plasma membrane and adjacent ER. Restoration of extracellular Ca(2+) causes localized Ca(2+) influx that first increases [Ca(2+)](SPM) in the same restricted regions and then, with a delay, in ER-free regions. Antisense knockdown of the TRPC1 gene, proposed to encode endogenous SOCs, markedly reduces SOCE measured with Fura-2. High resolution immunocytochemistry with anti-TRPC1 antibody reveals that these TRPC-encoded SOCs are confined to the PM microdomains adjacent to the underlying 'junctional' ER. Thus, Ca(2+) entry through TRPC-encoded SOCs is closely linked, not only functionally, but also structurally, to the ER Ca(2+) stores.

The role of mitochondria for Ca2+ refilling of the endoplasmic reticulum

Endoplasmic reticulum (ER) Ca2+ refilling is an active process to ensure an appropriate ER Ca2+ content under basal conditions and to maintain or restore ER Ca2+ concentration during/after cell stimulation. The mechanisms to achieve successful ER Ca2+ refilling are multiple and built on a concerted action of processes that provide a suitable reservoir for Ca2+ sequestration into the ER. Despite mitochondria having been found to play an essential role in the maintenance of capacitative Ca2+ entry by buffering subplasmalemmal Ca2+, their contribution to ER Ca2+ refilling was not subjected to detailed analysis so far. Thus, this study was designed to elucidate the involvement of mitochondria in Ca2+ store refilling during and after cell stimulation. ER Ca2+ refilling was found to be accomplished even during continuous inositol 1,4,5-trisphosphate (IP3)-triggered ER Ca2+ release by an agonist. Basically, ER Ca2+ refilling depended on the presence of extracellular Ca2+ as the source and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity. Interestingly, in the presence of an IP3-generating agonist, ER Ca2+ refilling was prevented by the inhibition of trans-mitochondrial Ca2+ flux by CGP 37157 (7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one) that precludes the mitochondrial Na+/Ca2+ exchanger as well as by mitochondrial depolarization using a mixture of oligomycin and antimycin A. In contrast, after the removal of the agonist, ER refilling was found to be largely independent of trans-mitochondrial Ca2+ flux. Under these conditions, ER Ca2+ refilling took place even without an associated Ca2+ elevation in the deeper cytosol, thus, indicating that superficial ER domains mimic mitochondrial Ca2+ buffering and efficiently sequester subplasmalemmal Ca2+ and consequently facilitate capacitative Ca2+ entry. Hence, these data point to different contribution of mitochondria in the process of ER Ca2+ refilling based on the presence or absence of IP3, which represents the turning point for the dependence or autonomy of ER Ca2+ refilling from trans-mitochondrial Ca2+ flux.

Kisspeptin-10, a KiSS-1/metastin-derived decapeptide, is a physiological invasion inhibitor of primary human trophoblasts

Trophoblast invasion of the uterine extracellular matrix, a critical process of human implantation and essential for fetal development, is a striking example of controlled invasiveness. To identify molecules that regulate trophoblast invasion, mRNA signatures of trophoblast cells isolated from first trimester (high invasiveness) and term placentae (no/low invasiveness) were compared using U95A GeneChip microarrays yielding 220 invasion/migration-related genes. In this 'invasion cluster', KiSS-1 and its G-protein-coupled receptor KiSS-1R were expressed at higher levels in first trimester trophoblasts than at term of gestation. Receptor and ligand mRNA and protein were localized to the trophoblast compartment. In contrast to KiSS-1, which is only expressed in the villous trophoblast, KiSS-1R was also found in the extravillous trophoblast, suggesting endocrine/paracrine activation mechanisms. The primary translation product of KiSS-1 is a 145 amino acid polypeptide (Kp-145), but shorter kisspeptins (Kp) with 10, 13, 14 or 54 amino acid residues may be produced. We identified Kp-10, a dekapeptide derived from the primary translation product, in conditioned medium of first trimester human trophoblast. Kp-10, but not other kisspeptins, increased intracellular Ca(2+) levels in isolated first trimester trophoblasts. Kp-10 inhibited trophoblast migration in an explant as well as transwell assay without affecting proliferation. Suppressed motility was paralleled with suppressed gelatinolytic activity of isolated trophoblasts. These results identified Kp-10 as a novel paracrine/endocrine regulator in fine-tuning trophoblast invasion generated by the trophoblast itself.

Hyperglycemic Conditions Affect Shape and Ca2+ Homeostasis of Mitochondria in Endothelial Cells

In this study the contribution of alternating architecture and Ca2+ handling of mitochondria to cytosolic Ca2+ homeostasis was elucidated under normoglycemic and hyperglycemic (HGC) conditions in the human endothelial cell line EA.hy926. Exposure of endothelial cells to hyperglycemic medium elevated basal cytosolic free Ca2+ concentration ([Ca2+]cyto), the histamine-initiated cytosolic Ca2+ signaling, and the mitochondrial Ca2+ content after cell stimulation. The latter was possibly due to the prolonged mitochondrial Ca2+ elevation in response to agonists found in HGC-pretreated cells. Moreover, under HGC mitochondrial free radical production was increased and mitochondrial shape changed from a mainly tubular, highly interconnected network toward multiple, isolated singular structures. Such changes could not be correlated with HGC-induced alterations of cytosolic Ca2+ signaling that became normalized with antimycin A, an inhibitor of the respiratory chain. These data suggest that although mitochondrial structure changes considerably during HGC, alterations in cytosolic Ca2+ signaling are more likely due to the enhanced energy status/metabolism of the mitochondria. On the other hand, in normoglycemic cells of unforced fragmentation of mitochondria yielded elevated basal [Ca2+]cyto, while the global Ca2+ signaling in response to histamine remained unchanged. Thus, mitochondrial architecture (ie, tubular versus fragmented structure) per se does not have a detectable impact on agonist-initiated global cytosolic Ca2+ signaling, while this organelle represents an early target in hyperglycemia leading to alterations in cytosolic Ca2+ signaling.

Sodium-calcium exchanger contributes to membrane hyperpolarization of intact endothelial cells from rat aorta during acetylcholine stimulation

1. The role of sodium-calcium exchanger in acetylcholine (Ach)-induced hyperpolarization of intact endothelial cells was studied in excised rat aorta. The membrane potential was recorded using perforated patch-clamp technique. 2. The mean resting potential of endothelial cells was -44.1+/-1.4 mV. A selective inhibitor of sodium-calcium exchanger benzamil (100 microm) had no significant effect on resting membrane potential, but reversibly decreased the amplitude of sustained Ach-induced endothelial hyperpolarization from 20.9+/-1.4 to 5.7+/-1.1 mV when applied during the plateau phase. 3. The blocker of reversed mode of the exchanger KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate, 20 microm) reversibly decreased the amplitude of sustained Ach-induced hyperpolarization from 20.5+/-2.9 to 7.5+/-1.8 mV. 4. Introduction of tetraethylammonium (10 mm) in the continuous presence of Ach decreased the sustained phase of hyperpolarization from 17.9+/-1.5 by 12.9+/-0.9 mV. Subsequent addition of 20 microm KB-R7943 further depolarized endothelial cells by 4.8+/-1.1 mV. 5. Substituting external sodium with N-methyl d-glucamine during the plateau phase of Ach-evoked hyperpolarization reversibly decreased the hyperpolarization from -61.8+/-2.7 to -54.2+/-1.9 mV. In the majority of preparations, the initial response to removal of external sodium was a transient further rise in the membrane potential of several mV. Sodium ionophore monensin hyperpolarized endothelium by 10.3+/-0.7 mV. 6. The inhibitory effect of benzamil on Ach-induced endothelial sustained hyperpolarization was observed in endothelium mechanically isolated from smooth muscle. 7. These results suggest that the sodium-calcium exchanger of intact endothelial cells is able to operate in reverse following stimulation by Ach, contributing to sustained hyperpolarization. Myoendothelial electrical communications do not mediate the effect of blockers of sodium-calcium exchanger.

Calcium Dynamics and Vasomotion in Rat Mesenteric Arteries

Smooth muscle cell calcium dynamics and diameter were measured in intact pressurized rat mesenteric artery segments during vasoconstriction and vasomotion. Arteries showed a certain norepinephrine (NE) threshold (0.3-0.4 microM) for the onset of vasomotion, during a cumulative NE concentration-response curve. This was due to a necessary [Ca2+]i threshold (increase over basal level of 22.2 +/- 2.6%) to elicit oscillations. The calcium oscillations obtained were synchronous over the entire vessel length and phase-shifted (in advance by 1.7 +/- 0.3 seconds) with respect to the diameter oscillations. A similar result was obtained using a KCl depolarization to contract the arteries, even though the [Ca2+]i threshold was much smaller in this case (increase over basal level of 9.9 +/- 4.3%), as compared with the NE-elicited vasomotion. Blockade of the Na+/K+-ATPase with 1 microM ouabain, or of the Na+/Ca2+ exchanger (NCX) with 1 microM KB-R 7943, did not abolish the calcium oscillations, thus showing that these two pumps are only modulatory elements, while on the other hand, voltage-gated calcium channels have been found to be important in the vasomotion mechanism.

Exercise prevents diabetes-induced impairment in superficial buffer barrier in porcine coronary smooth muscle

In healthy coronary smooth muscle cells, the superficial sarcoplasmic reticulum (SR) buffers rise in intracellular Ca2+ levels. In diabetic dyslipidemia, basal Ca2+ levels are increased, yet Ca2+ influx is decreased and SR Ca2+ uptake is increased. Exercise prevents diabetic dyslipidemia-induced increases in basal Ca2+ levels and decreases in Ca2+ influx. We tested the hypothesis that diabetic dyslipidemia impairs Ca2+ extrusion via a decrease in superficial SR and that exercise will prevent these losses. Male Yucatan swine were maintained in four treatment groups: control, hyperlipidemic, diabetic dyslipidemic, and diabetic dyslipidemic plus aerobically exercise trained. Intracellular Ca2+ levels were measured during depolarization-induced Ca2+ influx and caffeine-induced SR Ca2+ release. Na+/Ca2+ exchanger and plasmalemmal Ca2+-ATPase activity were assessed by inhibition with low extracellular Na+ and 5,6-carboxyeosin, respectively. Superficial SR was quantified using the internal membrane dye 3,3′-dihexyloxacarbocyanine iodide (DiOC6) and novel analysis techniques. We found that, in diabetic dyslipidemia, Ca2+ extrusion was impaired and superficial SR was decreased. Exercise prevented the diabetic dyslipidemia-induced decrease in superficial SR and restored plasmalemmal Ca2+ extrusion. On the basis of these results, we conclude exercise attenuates the diabetic dyslipidemia-induced impairment in intracellular Ca2+ regulation.

Localized transient increases in endothelial cell Ca2+ in arterioles in situ: implications for coordination of vascular function

Intracellular Ca2+ transients were identified in endothelial cells (ECs) in intact blood-perfused arterioles. ECs in cremaster muscle arterioles (diameter approximately 45 microm) in anesthetized mice were loaded with the Ca2+ indicator fluo 4-AM by intraluminal perfusion, after which blood flow was reestablished. Confocal microscopy was used to visualize Ca2+ as a function of fluo-4 intensity in real time. Separate sets of experiments were performed under the following conditions: control, ischemia, during inhibition of P(2x) or P(1) purinoreceptors, and with the application of exogenous adenosine. In controls, spontaneous EC Ca2+ transients displayed a wide range of activity frequency (1-32 events/min) and about one-third of these transient events were synchronized between adjacent ECs. The increase in Ca2+ remained localized and did not spread to encompass the entire cell body. Ca2+ transient activity decreased significantly with ischemia (from 9.9 +/- 0.6 to 3.1 +/- 0.3 events/min, n = 135) but was unaffected by P(2x) or P(1) receptor inhibition. Exogenous adenosine significantly increased the frequency of Ca2+ transients (to 12.8 +/- 0.9 events/min) and increased synchronization so that 50% of all Ca2+ events were synchronized between ECs. This response to adenosine was not due to an increase in shear stress. These data indicate that localized Ca2+ transients are sensitive to flow conditions and, separately, to metabolically active pathways (exogenous adenosine), although the basal activity occurs independently of P(2x) or P(1) receptors. These transients may represent a mechanism by which individual EC responses are integrated to result in coordinated arteriolar responses in situ.

Ca(2+) signaling by TRPC3 involves Na(+) entry and local coupling to the Na(+)/Ca(2+) exchanger

TRPC3 has been suggested as a key component of phospholipase C-dependent Ca(2+) signaling. Here we investigated the role of TRPC3-mediated Na(+) entry as a determinant of plasmalemmal Na(+)/Ca(2+) exchange. Ca(2+) signals generated by TRPC3 overexpression in HEK293 cells were found to be dependent on extracellular Na(+), in that carbachol-stimulated Ca(2+) entry into TRPC3 expressing cells was significantly suppressed when extracellular Na(+) was reduced to 5 mm. Moreover, KB-R9743 (5 microm) an inhibitor of the Na(+)/Ca(2+) exchanger (NCX) strongly suppressed TRPC3-mediated Ca(2+) entry but not TRPC3-mediated Na(+) currents. NCX1 immunoreactivity was detectable in HEK293 as well as in TRPC3-overexpressing HEK293 cells, and reduction of extracellular Na(+) after Na(+) loading with monensin resulted in significant rises in intracellular free Ca(2+) (Ca(2+)(i)) of HEK293 cells. Similar rises in Ca(2+)(i) were recorded in TRPC3-overexpressing cells upon the reduction of extracellular Na(+) subsequent to stimulation with carbachol. These increases in Ca(2+)(i) were associated with outward membrane currents at positive potentials and inhibited by KB-R7943 (5 microm), chelation of extracellular Ca(2+), or dominant negative suppression of TRPC3 channel function. This suggests that Ca(2+) entry into TRPC3-expressing cells involves reversed mode Na(+)/Ca(2+) exchange. Cell fractionation experiments demonstrated co-localization of TRPC3 and NCX1 in low density membrane fractions, and co-immunoprecipitation experiments provided evidence for association of TRPC3 and NCX1. Glutathione S-transferase pull-down experiments revealed that NCX1 interacts with the cytosolic C terminus of TRPC3. We suggest functional and physical interaction of nonselective TRPC cation channels with NCX proteins as a novel principle of TRPC-mediated Ca(2+) signaling.

Increase in endothelial cell Ca(2+) in response to mouse cremaster muscle contraction

We addressed the role of endothelial cells (ECs) in metabolic dilatation of skeletal muscle arterioles in anaesthetized mice in situ. Electrical field stimulation was used to contract the cremaster muscle for 15 s at 30 Hz. Diameter was observed using bright field microscopy. In controls, muscle contraction produced a 15.7 +/- 1.5 microm dilatation from a baseline of 17.4 +/- 1.6 microm. Endothelial denudation (-EC) via intraluminal perfusion of air abolished this response (1.6 +/- 1.2 microm in -EC, P < 0.05), identifying endothelium as the primary vascular cell type initiating the dilatation. To investigate the role of EC Ca(2+) in metabolic dilatation, arteriolar ECs were loaded with Fluo-4 AM or BAPTA AM by intraluminal perfusion, after which blood flow was re-established. Ca(2+) activity of individual ECs was monitored as a function of change from baseline fluorescence using confocal microscopy. In ECs, whole cell Ca(2+) increased (>10%, P < 0.05) during muscle contraction, and localized Ca(2+) transients were increased (>20%, P < 0.05) during the first minute after contraction. Chelation of EC Ca(2+) abolished the dilatations in response to muscle contraction (1.1 +/- 0.7 microm, P < 0.05). Inhibition of P(1) purinergic receptors (with xanthine amine congener) did not alter the rate of onset of the dilatation (P > 0.05) but decreased its magnitude immediately post stimulation (7.1 +/- 0.9 microm, P < 0.05) and during recovery. These findings demonstrate obligatory roles for endothelium and EC Ca(2+) during metabolic dilatation in intact arterioles. Furthermore, they suggest that at least two separate pathways mediate the local response, one of which involves stimulation of endothelial P(1) purinergic receptors via endogenous adenosine produced during muscle activity.

Anandamide initiates Ca(2+) signaling via CB2 receptor linked to phospholipase C in calf pulmonary endothelial cells

The endocannabinoid anandamide has been reported to affect neuronal cells, immune cells and smooth muscle cells via either CB1 or CB2 receptors. In endothelial cells, the receptors involved in activating signal transduction are still unclear, despite the fact that anandamide is produced in this cell type. The present study was designed to explore in detail the effect of this endocannabinoid on Ca2+ signaling in single cells of a calf pulmonary endothelial cell line. Anandamide initiated a transient Ca2+ elevation that was prevented by the CB2 receptor antagonist SR144528, but not by the CB1 antagonist SR141716A. These data were confirmed by molecular identification of the bovine CB2 receptor in these endothelial cells by partial sequencing. The phospholipase C inhibitor 1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5dione and the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenylborate prevented Ca2+ signaling in response to anandamide. Using an improved cameleon probe targeted to the endoplasmic reticulum (ER), fura-2 and ratiometric-pericam, which is targeted to the mitochondria, anandamide was found to induce Ca2+ depletion of the ER accompanied by the activation of capacitative Ca2+ entry (CCE) and a transient elevation of mitochondrial Ca2+. These data demonstrate that anandamide stimulates the endothelial cells used in this study via CB2 receptor-mediated activation of phospholipase C, formation of inositol 1,4,5-trisphosphate, Ca2+ release from the ER and subsequent activation of CCE. Moreover, the cytosolic Ca2+ elevation was accompanied by a transient Ca2+ increase in the mitochondria. Thus, in addition to its actions on smooth muscle cells, anandamide also acts as a powerful stimulus for endothelial cells.

Mitochondria efficiently buffer subplasmalemmal Ca2+ elevation during agonist stimulation

In endothelial cells, local Ca(2+) release from superficial endoplasmic reticulum (ER) activates BK(Ca) channels. The resulting hyperpolarization promotes capacitative Ca(2+) entry (CCE), which, unlike BK(Ca) channels, is inhibited by high Ca(2+). To understand how the coordinated activation of plasma membrane ion channels with opposite Ca(2+) sensitivity is orchestrated, the individual contribution of mitochondria and ER in regulation of subplasmalemmal Ca(2+) concentration ([Ca(2+)](pm)) was investigated. For organelle visualization, cells were transfected with DsRed and yellow cameleon targeted to mitochondria and ER. The patch pipette was placed far from any organelle (L1), close to ER (L3), or mitochondria (L2) and activity of BK(Ca) channels was used to estimate local [Ca(2+)](pm). Under standard patch conditions (130 mm K(+) in the bath), histamine increased [Ca(2+)](pm) at L1 and L3 to approximately 1.6 microm, whereas close to mitochondria [Ca(2+)](pm) remained unchanged. If mitochondria moved apart from the pipette or in the presence of carbonyl cyanide-4-trifluoromethoxyphenylhyrazone, [Ca(2+)](pm) at L2 increased in response to histamine. Under standard patch conditions Ca(2+) entry was negligible due to cell depolarization. Using a physiological patch approach (5.6 mm K(+) in the bath), changes in [Ca(2+)](pm) to histamine could be monitored without cell depolarization and, thus, in conditions where Ca(2+) entry occurred. Here, histamine induced an initial transient Ca(2+) elevation to > or =3.5 microm followed by a long lasting plateau at approximately 1.2 microm in L1 and L3, whereas mitochondria kept neighboring [Ca(2+)](pm) low during stimulation. Thus, superficial mitochondria and ER generate local domains of low and high Ca(2+) allowing simultaneous activation of BK(Ca) and CCE, despite their opposite Ca(2+) sensitivity.

Exercise training attenuates coronary smooth muscle phenotypic modulation and nuclear Ca2+ signaling

Physical inactivity is an independent risk factor for coronary heart disease, yet the mechanism(s) of exercise-related cardioprotection remains unknown. We tested the hypothesis that coronary smooth muscle after exercise training would have decreased mitogen-induced phenotypic modulation and enhanced regulation of nuclear Ca(2+). Yucatan swine were endurance exercise trained (EX) on a treadmill for 16-20 wk. EX reduced endothelin-1-induced DNA content by 40% compared with sedentary (SED) swine (P < 0.01). EX decreased single cell peak endothelin-1-induced cytosolic Ca(2+) responses compared with SED by 16% and peak nuclear Ca(2+) responses by 33% (P < 0.05), as determined by confocal microscopy. On the basis of these results, we hypothesized that sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) and intracellular Ca(2+) stores in native smooth muscle are spatially localized to dissociate cytosolic Ca(2+) and nuclear Ca(2+). Subcellular localization of SERCA in living and fixed cells revealed a distribution of SERCA near the sarcolemma and on the nuclear envelope. These results show that EX enhances nuclear Ca(2+) regulation, possibly via SERCA, which may be one mechanism by which coronary smooth muscle cells from EX are less responsive to mitogen-induced phenotypic modulation.

Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

We have previously identified alpha-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that alpha-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)-induced contraction of rat aortic rings. Addition of 1 microM alpha-defensin increased the half-maximal effective concentration (EC(50)) of PE on denuded aortic rings from 32 to 630 nM. The effect of alpha-defensin was dose dependent and saturable, with a half-maximal effect at 1 microM. alpha-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 microM alpha-defensin inhibited the PE-mediated Ca(++) mobilization in SMCs by more than 80%. The inhibitory effect of alpha-defensin on contraction of aortic rings and Ca(++) mobilization was completely abolished by anti-low-density lipoprotein receptor-related protein/alpha(2-)macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). alpha-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. alpha-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, alpha and beta. RAP and anti-LRP antibodies inhibited the binding and internalization of alpha-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of alpha-defensin to LRP expressed in SMCs leads to its internalization; internalized alpha-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca(++) mobilization and SMC contraction in response to PE.

Nitric oxide inhibits capacitative Ca2+ entry by suppression of mitochondrial Ca2+ handling

1. Nitric oxide (NO) is a key modulator of cellular Ca(2+) signalling and a determinant of mitochondrial function. Here, we demonstrate that NO governs capacitative Ca(2+) entry (CCE) into HEK293 cells by impairment of mitochondrial Ca(2+) handling. 2. Authentic NO as well as the NO donors 1-[2-(carboxylato)pyrrolidin-1-yl]diazem-1-ium-1,2-diolate (ProliNO) and 2-(N,N-diethylamino)-diazenolate-2-oxide (DEANO) suppressed CCE activated by thapsigargin (TG)-induced store depletion. Threshold concentrations for inhibition of CCE by ProliNO and DEANO were 0.3 and 1 micro M, respectively. 3. NO-induced inhibition of CCE was not mimicked by peroxynitrite (100 micro M), the peroxynitrite donor 3-morpholino-sydnonimine (SIN-1, 100 micro M) or 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP, 1 mM). In addition, the guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazole[4,3-a] quinoxalin-1-one (ODQ, 30 micro M) failed to antagonize the inhibitory action of NO on CCE. 4. DEANO (1-10 micro M) suppressed mitochondrial respiration as evident from inhibition of cellular oxygen consumption. Experiments using fluorescent dyes to monitor mitochondrial membrane potential and mitochondrial Ca(2+) levels, respectively, indicated that DEANO (10 micro M) depolarized mitochondria and suppressed mitochondrial Ca(2+) sequestration. The inhibitory effect of DEANO on Ca(2+) uptake into mitochondria was confirmed by recording mitochondrial Ca(2+) during agonist stimulation in HEK293 cells expressing ratiometric-pericam in mitochondria. 5. DEANO (10 micro M) failed to inhibit Ba(2+) entry into TG-stimulated cells when extracellular Ca(2+) was buffered below 1 micro M, while clear inhibition of Ba(2+) entry into store depleted cells was observed when extracellular Ca(2+) levels were above 10 micro M. Moreover, buffering of intracellular Ca(2+) by use of N,N'-[1,2-ethanediylbis(oxy-2,1-phenylene)] bis [N-[25-[(acetyloxy) methoxy]-2-oxoethyl]]-, bis[(acetyloxy)methyl] ester (BAPTA/AM) eliminated inhibition of CCE by NO, indicating that the observed inhibitory effects are based on an intracellular, Ca(2+) dependent-regulatory process. 6. Our data demonstrate that NO effectively inhibits CCE cells by cGMP-independent suppression of mitochondrial function. We suggest disruption of local Ca(2+) handling by mitochondria as a key mechanism of NO induced suppression of CCE.

Involvement of Na(+)/Ca(2+) exchanger in endothelial NO production and endothelium-dependent relaxation

Endothelial nitric oxide (NO) synthase (eNOS) is controlled by Ca(2+)/calmodulin and caveolin-1 in caveolae. It has been recently suggested that Na(+)/Ca(2+) exchanger (NCX), also expressed in endothelial caveolae, is involved in eNOS activation. To investigate the role played by NCX in NO synthesis, we assessed the effects of Na(+) loading (induced by monensin) on rat aortic rings and cultured porcine aortic endothelial cells. Effect of monensin was evaluated by endothelium-dependent relaxation of rat aortic rings in response to acetylcholine and by real-time measurement of NO release from cultured endothelial cells stimulated by A-23187 and bradykinin. Na(+) loading shifted the acetylcholine concentration-response curve to the left. These effects were prevented by pretreatment with the NCX inhibitors benzamil and KB-R7943. Monensin potentiated Ca(2+)-dependent NO release in cultured cells, whereas benzamil and KB-R7943 totally blocked Na(+) loading-induced NO release. These findings confirm the key role of NCX in reverse mode on Ca(2+)-dependent NO production and endothelium-dependent relaxation.

Functional analysis of histamine receptor subtypes involved in endothelium-mediated relaxation of the human uterine artery

1. This work was designed to introduce human uterine arteries as a new model for cardiovascular research. Advantages of this model include considerable availability of tissue because of the appearance of uterus myomatosus in post-menopausal women who undergo surgery and the chance to work on dysfunctional and healthy vessels. 2. Histamine evoked relaxation of the uterine artery that was prevented by removal of the endothelium or by the presence of N(G)-nitro-L-arginine. 3. Receptor antagonists for histamine H(1) (mepyramine) and H(2) (ranitidine) receptors increased the EC(50) of histamine by 112- and 67-fold, respectively. 4. Remarkably, isolated uterine arteries could be stored in incubators for 5 days without any change in contractility to phenylephrine and endothelium-dependent relaxation to acetylcholine and histamine. 5. Endothelial cells could be isolated and cultured in high purity, as demonstrated by histochemical staining of factor VIII, low CD45-RO for macrophages and no smooth muscle alpha-actin. In addition, cultured human uterine artery endothelial cells could be used for single cell Ca(2+) measurements. 6. In agreement with our findings in the intact vessel, histamine-initiated elevation of the intracellular free Ca(2+) concentration was reduced in the presence of mepyramine and ranitidine by 59 and 55%, respectively. 7. These data indicate that, in the human uterine artery, H(1) and H(2) receptors are involved in histamine-induced endothelium-dependent relaxation that is mediated by nitric oxide. 8. In addition, this vessel can be stored for possible virus-mediated gene expression for 5 days without any loss of reagibility. 9. Finally, endothelial cells can be isolated and cultured from the human uterine artery and maintain their reactivity to histamine in culture.

Endothelin-induced myoplasmic Ca2+ responses and tyrosine phosphorylation in coronary smooth muscle

This study investigated the role of tyrosine phosphorylation and source of Ca2+ in prolonged endothelin-1 (ET-1)-induced potentiation of myoplasmic free Ca2+ ([Ca2+]m) responses to depolarization in coronary smooth muscle cells. Fura-2 microfluorometry showed typical increases in [Ca2+]m in response to 80 mM K+ (80K) and 0.01 microM endothelin. After washout of ET-1 80K-induced [Ca2+]m increases were augmented (potentiated) 31%. Time to peak [Ca2+]m response to 80K was less after ET-1 exposure than before. ET-1 potentiation of 80K-induced [Ca2+]m responses by decreased sarcoplasmic reticulum (SR) buffering of [Ca2+]m or Ca2+-induced Ca2+ release was ruled out by lack of potentiation by 5 mM caffeine and 1 microM thapsigargin. Diltiazem abolished potentiation, providing evidence for Ca2+ influx through voltage-gated Ca2+ channels (VGCC). Genistein (30 microM) and methyl 2,5-dihydroxycinnamate (1 microM, MDHC) abolished potentiation of Ca2+ influx. Single cell phosphotyrosine measured directly by immunofluorescence was increased 95% in cells treated with ET-1 compared to control, genistein, and MDHC treated cells. ET-1 increased tyrosine phosphorylation of an 80-85 kDa protein, but not the 240 kDa alpha1C subunit of the VGCC. Tyrosine phosphorylation of proteins other than VGCC is necessary for prolonged potentiation by ET-1 of depolarization-induced Ca2+ influx.