Phenotypic modulation of vascular myocytes is important for vascular development and adaptation. A characteristic feature of this process is alteration in intracellular Ca²⁺ handling, which is not completely understood. We studied mechanisms involved in functional changes of inositol 1,4,5-trisphosphate (IP₃)- and ryanodine (Ry)-sensitive Ca²⁺ stores, store-operated Ca²⁺ entry (SOCE), and receptor-operated Ca²⁺ entry (ROCE) associated with arterial myocyte modulation from a contractile to a proliferative phenotype in culture. Proliferating, cultured myocytes from rat mesenteric artery have elevated resting cytosolic Ca²⁺ levels and increased IP₃-sensitive Ca²⁺ store content. ATP- and cyclopiazonic acid [CPA; a sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) inhibitor]-induced Ca²⁺ transients in Ca²⁺-free medium are significantly larger in proliferating arterial smooth muscle cells (ASMCs) than in freshly dissociated myocytes, whereas caffeine (Caf)-induced Ca²⁺ release is much smaller. Moreover, the Caf/Ry-sensitive store gradually loses sensitivity to Caf activation during cell culture. These changes can be explained by increased expression of all three IP₃ receptors and a switch from Ry receptor type II to type III expression during proliferation. SOCE, activated by depletion of the IP₃/CPA-sensitive store, is greatly increased in proliferating ASMCs. Augmented SOCE and ROCE (activated by the diacylglycerol analog 1-oleoyl-2-acetyl- sn-glycerol) in proliferating myocytes can be attributed to upregulated expression of, respectively, transient receptor potential proteins TRPC1/4/5 and TRPC3/6. Moreover, stromal interacting molecule 1 (STIM1) and Orai proteins are upregulated in proliferating cells. Increased expression of IP₃ receptors, SERCA2b, TRPCs, Orai(s), and STIM1 in proliferating ASMCs suggests that these proteins play a critical role in an altered Ca²⁺ handling that occurs during vascular growth and remodeling.

A key question in hypertension is: How is long‐term blood pressure controlled? A clue is that chronic salt retention elevates an endogenous ouabain‐like compound (EOLC) and induces salt‐dependent hypertension mediated by Na⁺/Ca²⁺ exchange (NCX). The precise mechanism, however, is unresolved. Here we study blood pressure and isolated small arteries of mice with reduced expression of Na⁺ pump α1 (α1^+/−) or α2 (α2^+/−) catalytic subunits. Both low‐dose ouabain (1–100 nm; inhibits only α2) and high‐dose ouabain (≥1 μm; inhibits α1) elevate myocyte Ca²⁺ and constrict arteries from α1^+/−, as well as α2^+/− and wild‐type mice. Nevertheless, only mice with reduced α2 Na⁺ pump activity (α2^+/−), and not α1 (α1^+/−), have elevated blood pressure. Also, isolated, pressurized arteries from α2^+/−, but not α1^+/−, have increased myogenic tone. Ouabain antagonists (PST 2238 and canrenone) and NCX blockers (SEA0400 and KB‐R7943) normalize myogenic tone in ouabain‐treated arteries. Only the NCX blockers normalize the elevated myogenic tone in α2^+/− arteries because this tone is ouabain independent. All four agents are known to lower blood pressure in salt‐dependent and ouabain‐induced hypertension. Thus, chronically reduced α2 activity (α2^+/− or chronic ouabain) apparently regulates myogenic tone and long‐term blood pressure whereas reduced α1 activity (α1^+/−) plays no persistent role: the in vivo changes in blood pressure reflect the in vitro changes in myogenic tone. Accordingly, in salt‐dependent hypertension, EOLC probably increases vascular resistance and blood pressure by reducing α2 Na⁺ pump activity and promoting Ca²⁺ entry via NCX in myocytes.

Endothelial progenitor cells (EPCs) home from the bone marrow to the site of tissue regeneration and sustain neovascularization after acute vascular injury and upon the angiogenic switch in solid tumors. Therefore, they represent a suitable tool for cell-based therapy (CBT) in regenerative medicine and provide a novel promising target in the fight against cancer. Intracellular Ca2+ signals regulate numerous endothelial functions, such as proliferation and tubulogenesis. The growth of endothelial colony forming cells (ECFCs), which are EPCs capable of acquiring a mature endothelial phenotype, is governed by store-dependent Ca2+ entry (SOCE). This study aimed at investigating the nature and the role of VEGF-elicited Ca2+ signals in ECFCs. VEGF induced asynchronous Ca2+ oscillations, whose latency, amplitude, and frequency were correlated to the growth factor dose. Removal of external Ca2+ (0Ca2+) and SOCE inhibition with N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP-2) reduced the duration of the oscillatory signal. Blockade of phospholipase C-γ with U73122, emptying the inositol-1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools with cyclopiazonic acid (CPA), and inhibition of InsP3 receptors with 2-APB prevented the Ca2+ response to VEGF. VEGF-induced ECFC proliferation and tubulogenesis were inhibited by the Ca2+-chelant, BAPTA, and BTP-2. NF-κB activation by VEGF was impaired by BAPTA, BTP-2, and its selective blocker, thymoquinone. Thymoquinone, in turn, suppressed VEGF-dependent ECFC proliferation and tubulogenesis. These data indicate that VEGF-induced Ca2+ oscillations require the interplay between InsP3-dependent Ca2+ release and SOCE, and promote ECFC growth and tubulogenesis by engaging NF-κB. This novel signaling pathway might be exploited to enhance the outcome of CBT and chemotherapy.

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 Ca(2+) 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 Ca(2+) levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca(2+) signals, ranging from brief, localized Ca(2+) pulses to prolonged Ca(2+) oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca(2+) signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca(2+) releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca(2+) 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 Ca(2+) machinery in vascular ECs under both physiological and pathological conditions.

Ca²⁺ entry via L-type voltage-gated Ca²⁺ channels (LVGCs) is a key factor in generating myogenic tone (MT), as dihydropyridines (DHPs) and other LVGC blockers, including Mg²⁺, markedly reduce MT. Recent reports suggest, however, that elevated external Mg²⁺ concentration and DHPs may also inhibit other Ca²⁺-entry pathways. Here, we explore the contribution of LVGCs to MT in intact, pressurized mesenteric small arteries using mutant mice (DHP^R/R) expressing functional but DHP-insensitive Ca_v1.2 channels. In wild-type (WT), but not DHP^R/R, mouse arteries, nifedipine (0.3–1.0 μM) markedly reduced MT and vasoconstriction induced by high external K⁺ concentrations ([K⁺]_o), a measure of LVGC-mediated Ca²⁺ entry. Blocking MT and high [K⁺]_o-induced vasoconstriction by <1 μM nifedipine in WT but not in DHP^R/R arteries implies that Ca²⁺ entry via Ca_v1.2 LVGCs is obligatory for MT and that nifedipine inhibits MT exclusively by blocking LVGCs. We also examined the effects of Mg²⁺ on MT and LVGCs. High external Mg²⁺ concentration (10 mM) blocked MT, slowed the high [K⁺]_o-induced vasoconstrictions, and decreased their amplitude in WT and DHP^R/R arteries. To verify that these effects of Mg²⁺ are due to block of LVGCs, we characterized the effects of extracellular and intracellular Mg²⁺ on LVGC currents in isolated mesenteric artery myocytes. DHP-sensitive LVGC currents are inhibited by both external and internal Mg²⁺. The results indicate that Mg²⁺ relaxes MT by inhibiting Ca²⁺ influx through LVGCs. These data provide new information about the central role of Ca_v1.2 LVGCs in generating and maintaining MT in mouse mesenteric small arteries.

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ion channels that are activated by the neurotransmitter glutamate, mediate the slow component of excitatory neurotransmission in the central nervous system (CNS), and induce long-term changes in synaptic plasticity. NMDARs are non-selective cation channels that allow the influx of extracellular Na⁺ and Ca²⁺ and control cellular activity via both membrane depolarization and an increase in intracellular Ca²⁺ concentration. The distribution, structure, and role of neuronal NMDARs have been extensively investigated and it is now known that they also regulate crucial functions in the non-neuronal cellular component of the CNS, i.e., astrocytes and cerebrovascular endothelial cells. In addition, NMDARs are expressed in multiple peripheral organs, including heart and systemic and pulmonary circulations. Herein, we survey the most recent information available regarding the distribution and function of NMDARs within the cardiovascular system. We describe the involvement of NMDARs in the modulation of heart rate and cardiac rhythm, in the regulation of arterial blood pressure, in the regulation of cerebral blood flow, and in the blood–brain barrier (BBB) permeability. In parallel, we describe how enhanced NMDAR activity could promote ventricular arrhythmias, heart failure, pulmonary artery hypertension (PAH), and BBB dysfunction. Targeting NMDARs could represent an unexpected pharmacological strategy to reduce the growing burden of several life-threatening cardiovascular disorders.