The importance of NADPH oxidase (Nox) in hypoxic responses in hypoxia-sensing cells, including pulmonary artery smooth muscle cells (PASMCs), remains uncertain. In this study, using Western blot analysis we found that the major Nox subunits Nox1, Nox4, p22(phox), p47(phox), and p67(phox) were equivalently expressed in mouse pulmonary and systemic (mesenteric) arteries. However, acute hypoxia significantly increased Nox activity and translocation of p47(phox) protein to the plasma membrane in pulmonary, but not mesenteric, arteries. The Nox inhibitor apocynin and p47(phox) gene deletion attenuated the hypoxic increase in intracellular concentrations of reactive oxygen species and Ca(2+) ([ROS](i) and [Ca(2+)](i)), as well as contractions in mouse PASMCs, and abolished the hypoxic activation of Nox in pulmonary arteries. The conventional/novel protein kinase C (PKC) inhibitor chelerythrine, specific PKCepsilon translocation peptide inhibitor, and PKCepsilon gene deletion, but not the conventional PKC inhibitor GO6976, prevented the hypoxic increase in Nox activity in pulmonary arteries and [ROS](i) in PASMCs. The PKC activator phorbol 12-myristate 13-acetate could increase Nox activity in pulmonary and mesenteric arteries. Inhibition of mitochondrial ROS generation with rotenone or myxothiazol prevented hypoxic activation of Nox. Glutathione peroxidase-1 (Gpx1) gene overexpression to enhance H(2)O(2) removal significantly inhibited the hypoxic activation of Nox, whereas Gpx1 gene deletion had the opposite effect. Exogenous H(2)O(2) increased Nox activity in pulmonary and mesenteric arteries. These findings suggest that acute hypoxia may distinctively activate Nox to increase [ROS](i) through the mitochondrial ROS-PKCepsilon signaling axis, providing a positive feedback mechanism to contribute to the hypoxic increase in [ROS](i) and [Ca(2+)](i) as well as contraction in PASMCs.

In this study we examined the expression of RyR subtypes and the role of RyRs in neurotransmitter- and hypoxia-induced Ca2+ release and contraction in pulmonary artery smooth muscle cells (PASMCs). Under perforated patch clamp conditions, maximal activation of RyRs with caffeine or inositol triphosphate receptors (IP3Rs) with noradrenaline induced equivalent increases in [Ca2+]i and Ca2+-activated Cl− currents in freshly isolated rat PASMCs. Following maximal IP3-induced Ca2+ release, neither caffeine nor chloro-m-cresol induced a response, whereas prior application of caffeine or chloro-m-cresol blocked IP3-induced Ca2+ release. In cultured human PASMCs, which lack functional expression of RyRs, caffeine failed to affect ATP-induced increases in [Ca2+]i in the presence and absence of extracellular Ca2+. The RyR antagonists ruthenium red, ryanodine, tetracaine, and dantrolene greatly inhibited submaximal noradrenaline– and hypoxia-induced Ca2+ release and contraction in freshly isolated rat PASMCs, but did not affect ATP-induced Ca2+ release in cultured human PASMCs. Real-time quantitative RT-PCR and immunofluorescence staining indicated similar expression of all three RyR subtypes (RyR1, RyR2, and RyR3) in freshly isolated rat PASMCs. In freshly isolated PASMCs from RyR3 knockout (RyR3−/−) mice, hypoxia-induced, but not submaximal noradrenaline–induced, Ca2+ release and contraction were significantly reduced. Ruthenium red and tetracaine can further inhibit hypoxic increase in [Ca2+]i in RyR3−/− mouse PASMCs. Collectively, our data suggest that (a) RyRs play an important role in submaximal noradrenaline– and hypoxia-induced Ca2+ release and contraction; (b) all three subtype RyRs are expressed; and (c) RyR3 gene knockout significantly inhibits hypoxia-, but not submaximal noradrenaline–induced Ca2+ and contractile responses in PASMCs.

The molecular mechanisms underlying hypoxic responses in pulmonary and systemic arteries remain obscure. Here we for the first time report that acute hypoxia significantly increased total PKC and PKCɛ activity in pulmonary, but not mesenteric arteries, while these two tissues showed comparable PKCɛ protein expression and activation by the PKC activator phorbol 12-myristate 13-acetate. Hypoxia induced an increase in intracellular reactive oxygen species (ROS) generation in isolated pulmonary artery smooth muscle cells (PASMCs), but not in mesenteric artery SMCs. Inhibition of mitochondrial ROS generation with rotenone, myxothiazol, or glutathione peroxidase-1 overexpression, prevented hypoxia-induced increases in total PKC and PKCɛ activity in pulmonary arteries. The inhibitory effects of rotenone were reversed by exogenous hydrogen peroxide. A PKCɛ translocation peptide inhibitor or PKCɛ gene deletion decreased hypoxic increase in [Ca 2+ ] i in PASMCs, whereas the conventional PKC inhibitor GÖ6976 had no effect. These data suggest that acute hypoxia may specifically increase mitochondrial ROS generation, which subsequently activates PKC, particularly PKCɛ, contributing to hypoxia-induced increase in [Ca 2+ ] i and contraction in PASMCs. KeywordsHypoxia; protein kinase C; reactive oxygen species; mitochondria; intracellular calcium; pulmonary artery smooth muscle cells Hypoxic pulmonary vasoconstriction (HPV) is observed in isolated lungs, pulmonary arteries, and pulmonary artery smooth muscle cells (PASMCs). The pulmonary circulation differs from the systemic circulation in response to oxygen tension; pulmonary arteries constrict to physiological hypoxia (~ 20-60 mmHg PO 2 ), whereas systemic arteries vasodilate. The mechanisms for these opposing responses to hypoxia appear to lie within the vascular SMCs. Hypoxia increases intracellular Ca 2+ concentration ([Ca 2+ ] i ) and contracts PASMCs. In contrast, SMCs from systemic arteries display decreased [Ca 2+ ] i and relax in response to hypoxia. The response of PASMCs to acute hypoxia involves calcium entry through voltagedependent and store-operated Ca 2+ channels, as well as Ca 2+ release from the sarcoplasmic reticulum [1][2][3][4][5][6][7][8]. Hypoxia-dependent changes in reactive oxygen species (ROS) concentration have been proposed to mediate HPV by several laboratories, although the details of this hypothesis differ greatly [9; 10]. However, the signaling pathways underlying artery-specific, acute hypoxic vasoconstriction remain to be fully elucidated. AnimalsPKCɛ −/− mice were purchased from the Jackson Laboratory (Bar Harbor, ME); Swiss-Webster mice from Taconic (Germantown, NY). Glutathione peroxidase-1 (Gpx1) overexpression mice were generated and maintained as described previously [18]. All animal experiments were approved by the Institutional Animal Care and Use Committee of Albany Medical College. To examine the effects of pharmacological reagents, control experiments were carried out in cells or tissues from the same mice. For experimen...

Membrane depolarization activates voltage-dependent Ca 2+ channels (VDCCs) inducing Ca 2+ release via ryanodine receptors (RyRs), which is obligatory for skeletal and cardiac muscle contraction and other physiological responses. However, depolarization-induced Ca 2+ release and its functional importance as well as underlying signaling mechanisms in smooth muscle cells (SMCs) are largely unknown. Here we report that membrane depolarization can induce RyR-mediated local Ca 2+ release, leading to a significant increase in the activity of Ca 2+ sparks and contraction in airway SMCs. The increased Ca 2+ sparks are independent of VDCCs and the associated extracellular Ca 2+ influx. This format of local Ca 2+ release results from a direct activation of G protein-coupled, M 3 muscarinic receptors in the absence of exogenous agonists, which causes activation of Gq proteins and phospholipase C, and generation of inositol 1,4,5-triphosphate (IP 3 ), inducing initial Ca 2+ release through IP 3 receptors and then further Ca 2+ release via RyR2 due to a local Ca 2+ -induced Ca 2+ release process. These findings demonstrate an important mechanism for Ca 2+ signaling and attendant physiological function in SMCs.

Cerebral vascular dysfunction and associated diseases often occur in type-1 diabetes, but the underlying mechanisms are largely unknown. In this study, we sought to determine whether big-conductance, Ca(2+)-activated K(+) (BK) channels were impaired in vascular (cerebral artery) smooth muscle cells (CASMCs) from streptozotocin-induced type-1 diabetic mice using patch clamp, molecular biologic, and genetic approaches. Our data indicate that the frequency and amplitude of spontaneous transient outward currents (STOCs) are significantly decreased, whereas the activity of spontaneous Ca(2+) sparks is increased, in diabetic CASMCs. The sensitivity of BK channels to voltage, Ca(2+), and the specific inhibitor iberiotoxin are all reduced in diabetic myocytes. Diabetic mice show increased myogenic tone and decreased contraction in response to iberiotoxin in cerebral arteries and elevated blood pressure. The expression of the BK channel beta1, but not alpha-subunit protein, is markedly decreased in diabetic cerebral arteries. Diabetic impairment of BK channel activity is lost in CASMCs from BK channel beta1-subunit gene deletion mice. In conclusion, the BK channel beta1-subunit is impaired in type-1 diabetic vascular SMCs, resulting in increased vasoconstriction and elevated blood pressure, thereby contributing to vascular diseases in type-1 diabetes.

Background: Hypoxia causes heterogeneous contractile responses in resistance and conduit pulmonary as well as systemic (mesenteric) artery smooth muscle cells (RPASMCs, CPASMCs and MASMCs), but the underlying mechanisms are largely unknown. In this study, we aimed to investigate whether the gene expression and functional activity of ryanodine receptors (RyRs) would be different in these 3 cell types. Methods: RyR mRNA expression, Ca²⁺ sparks and [Ca²⁺]_i were measured by real-time quantitative RT-PCR, laser scanning confocal microscopy and wide-field fluorescence microscopy, respectively. Results: All 3 RyR subtype (RyR1, RyR2 and RyR3) mRNAs are expressed in RPASMCs, CPASMCs and MASMCs, but their expression levels are different. Spontaneous Ca²⁺ sparks (functional events of RyRs) show distinct frequency, amplitude, duration, size and kinetics in these 3 cell types. Similarly, activation of RyRs by caffeine, 4-chloro-m-cresol or high K⁺ induces differential Ca²⁺ release. Moreover, hypoxia-induced increase in [Ca²⁺]_i is largest in MASMCs relative to CPSAMCs and smallest in RPASMCs. Conclusion: This study provides comprehensive evidence that RyRs are heterogeneous in gene expression and functional activity in RPASMCs, CPASMCs and MASMCs, which may contribute to the diversity of excitation-contraction coupling and hypoxic Ca²⁺ responses in different vascular smooth muscle cells.

Ryanodine receptor 1 (RyR1) is well-known to be expressed in systemic and pulmonary vascular smooth muscle cells (SMCs); however, its functional roles remain largely unknown. In the present study, we attempted to determine the potential importance of RyR1 in membrane depolarization-, neurotransmitter-, and hypoxia-induced Ca2+ release and contraction in pulmonary artery SMCs (PASMCs) using RyR1 homozygous and heterozygous gene deletion (RyR1−/− and RyR1+/−) mice. Our results indicate that spontaneous local Ca2+ release and caffeine-induced global Ca2+ release are significantly reduced in embryonic RyR1−/− and adult RyR+/− cells. An increase in [Ca2+]i following membrane depolarization with high K+ is markedly attenuated in RyR1−/− and RyR1+/− PASMCs in normal Ca2+ or Ca2+-free extracellular solution. Similarly, muscle contraction evoked by membrane depolarization is reduced in RyR1+/− pulmonary arteries in the presence or absence of extracellular Ca2+. Neurotransmitter receptor agonists and inositol 1,4,5-triphosphate elicit a much smaller increase in [Ca2+]i in both RyR1−/− and RyR1+/− cells. We have also found that neurotransmitter-evoked muscle contraction is significantly inhibited in RyR1+/− pulmonary arteries. Hypoxia-induced increase in [Ca2+]i and contraction are largely blocked in RyR1−/− and/or RyR1+/− PASMCs. Collectively, our findings provide genetic evidence for the functional importance of RyR1 in spontaneous local Ca2+ release, and membrane depolarization-, neurotransmitter-, as well as hypoxia-induced global Ca2+ release and attendant contraction in PASMCs.

Commonly used methods for isolated enzyme inhibitor screening typically rely on fluorescent or chemiluminescent detection techniques that are often indirect and/or coupled assays. Mass spectrometry (MS) has been widely reported for measuring the conversion of substrates to products for enzyme assays and has more recently been demonstrated as an alternative readout system for inhibitor screening. In this report, a high-throughput mass spectrometry (HTMS) readout platform, based on the direct measurement of substrate conversion to product, is presented. The rapid ionization and desorption features of a new generation matrix-assisted laser desorption ionization-triple quadrupole (MALDI-QqQ) mass spectrometer are shown to improve the speed of analysis to greater than 1 sample per second while maintaining excellent Z′ values. Furthermore, the readout was validated by demonstrating the ability to measure IC 50 values for several known kinase inhibitors against cyclic AMP-dependent protein kinase (PKA). Finally, when the assay performance was compared with a common ADPaccumulation readout system, this HTMS approach produced better signal-to-background ratios, higher Z′ values, and a reagent cost of about $0.03 per well compared with about $0.60 per well for the fluorescence assay. Collectively, these data demonstrate that a MALDI-QqQ-MS-based readout platform offers significant advantages over the commonly used assays in terms of speed, sensitivity, reproducibility, and reagent cost. INTRODUCTION HIGH-THROUGHPUT SCREENING (HTS) plays a central role in the drug discovery process starting at the early "hit" discovery stage then continuing through to lead optimization. As such, the screening community has continuously developed new technologies to meet the broadening assay needs and to expedite the work flow of drug discovery. Within the pharmaceutical and biotechnology enzyme screening community, fluorescent-and chemiluminescent-based detection methods continue to be the routine assay platforms of choice for isolated enzyme assays. These assays are desirable because they have been developed to be simple homogeneous assays that often offer universal methods to evaluate a variety of targets using the same reagents. However, 1 of the primary challenges for these approaches continues to be how to maintain the high speed of analysis while minimizing false-positive or false-negative readouts. Inherent to this challenge is the nature of fluorescence and chemiluminescence readout, which can lend itself to false readouts because of the properties of various compound classes that enhance or quench the signals. Thus a comparable approach in speed, robust readout, and cost that further minimizes the potential for false readouts would be a benefit to the field.One approach that offers promise in this arena is mass spectrometry. A variety of mass spectrometry (MS) techniques have been used to measure enzyme activity, enzyme kinetics, inhibition, and more recently for HTS applications (reviewed in the studies of Greis 1 and De Boer et...