Ca2+ channel-sarcoplasmic reticulum coupling: A mechanism of arterial myocyte contraction without Ca2+ influx

Laboratorio de Investigaciones Biomédicas, Departamento de Fisiología and Hospital Universitario Virgen del Rocío, Universidad de Sevilla, E-41013, Seville, Spain.
The EMBO Journal (Impact Factor: 10.43). 10/2003; 22(17):4337-45. DOI: 10.1093/emboj/cdg432
Source: PubMed


Contraction of vascular smooth muscle cells (VSMCs) depends on the rise of cytosolic [Ca2+] owing to either Ca2+ influx through voltage-gated Ca2+ channels of the plasmalemma or receptor-mediated Ca2+ release from the sarcoplasmic reticulum (SR). We show that voltage-gated Ca2+ channels in arterial myocytes mediate fast Ca2+ release from the SR and contraction without the need of Ca2+ influx. After sensing membrane depolarization, Ca2+ channels activate G proteins and the phospholipase C-inositol 1,4,5-trisphosphate (InsP3) pathway. Ca2+ released through InsP3-dependent channels of the SR activates ryanodine receptors to amplify the cytosolic Ca2+ signal. These observations demonstrate a new mechanism of signaling SR Ca(2+)-release channels and reveal an unexpected function of voltage-gated Ca2+ channels in arterial myocytes. Our findings may have therapeutic implications as the calcium-channel-induced Ca2+ release from the SR can be suppressed by Ca(2+)-channel antagonists.

  • Source
    • "While most vascular smooth muscle expresses all 3 known RyR isoforms (RyR1–3), it is primarily the activation of RyR1 and RyR2 that regulates excitation–contraction coupling [2]. These receptors are activated by Ca 2+ , and can act as amplifiers of smaller Ca 2+ signals caused by Ca 2+ influx or inositol 1,4,5-trisphosphate (IP 3 )-mediated Ca 2+ release [3]. This amplification, called " Ca 2+ induced Ca 2+ release " (CICR), mobilizes large amounts of SR Ca 2+ into the cytosol and has been proposed to serve an important role in excitation–contraction coupling in smooth muscle [4]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Ryanodine receptors (RyR) are Ca(2+)-sensitive ion channels in the sarcoplasmic reticulum (SR) membrane, and are important effectors of SR Ca(2+) release and smooth muscle excitation-contraction coupling. While the relationship between RyR activation and contraction is well characterized in arteries, little is known about the role of RyR in excitation-contraction coupling in veins. We hypothesized that RyR are present and directly coupled to contraction in rat aorta (RA) and vena cava (RVC). RA and RVC expressed mRNA for all 3 RyR subtypes, and immunofluorescence showed RyR protein was present in RA and RVC smooth muscle cells. RA and RVC rings contracted when Ca(2+) was re-introduced after stores depletion with thapsigargin (1μM), indicating both tissues contained intracellular Ca(2+) stores. To assess RyR function, contraction was then measured in RA and RVC exposed to the RyR activator caffeine (20mM). In RA, caffeine caused contraction that was attenuated by the RyR antagonists ryanodine (10μM) and tetracaine (100μM). However, caffeine (20mM) did not contract RVC. We next measured contraction and intracellular Ca(2+) (Ca(2+)(i)) simultaneously in RA and RVC exposed to caffeine. While caffeine increased Ca(2+)(i) and contracted RA, it had no significant effect on Ca(2+)(i) or contraction in RVC. These data suggest that ryanodine receptors, while present in both RA and RVC, are inactive and uncoupled from Ca(2+) release and contraction in RVC.
    Full-text · Article · Nov 2012 · Cell calcium
  • Source
    • "The endothelial murine cell line (EOMA cells, ATCC catalog no.: CRL-2586) derived from a mixed hemangioendothelioma was cultured at 37°C and 10% CO2 in DMEM with 4.5 g/L glucose, supplemented with 4 mM L-glutamine and 10% fetal bovine serum (BioWhittaker, Belgium). Primary cultures of pulmonary artery smooth muscle cells were obtained following previously described protocols [23]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Aquaporin-1 (AQP1) is a water channel that is highly expressed in tissues with rapid O(2) transport. It has been reported that this protein contributes to gas permeation (CO(2), NO and O(2)) through the plasma membrane. We show that hypoxia increases Aqp1 mRNA and protein levels in tissues, namely mouse brain and lung, and in cultured cells, the 9L glioma cell line. Stopped-flow light-scattering experiments confirmed an increase in the water permeability of 9L cells exposed to hypoxia, supporting the view that hypoxic Aqp1 up-regulation has a functional role. To investigate the molecular mechanisms underlying this regulatory process, transcriptional regulation was studied by transient transfections of mouse endothelial cells with a 1297 bp 5' proximal Aqp1 promoter-luciferase construct. Incubation in hypoxia produced a dose- and time-dependent induction of luciferase activity that was also obtained after treatments with hypoxia mimetics (DMOG and CoCl(2)) and by overexpressing stabilized mutated forms of HIF-1α. Single mutations or full deletions of the three putative HIF binding domains present in the Aqp1 promoter partially reduced its responsiveness to hypoxia, and transfection with Hif-1α siRNA decreased the in vitro hypoxia induction of Aqp1 mRNA and protein levels. Our results indicate that HIF-1α participates in the hypoxic induction of AQP1. However, we also demonstrate that the activation of Aqp1 promoter by hypoxia is complex and multifactorial and suggest that besides HIF-1α other transcription factors might contribute to this regulatory process. These data provide a conceptual framework to support future research on the involvement of AQP1 in a range of pathophysiological conditions, including edema, tumor growth, and respiratory diseases.
    Full-text · Article · Dec 2011 · PLoS ONE
  • Source
    • "Values are presented as meanSEM. *P0.05, **P0.01.14,25,20We now show that in normal conditions, CCICR mediates Ca 2 release and sensitization of the contractile apparatus necessary to generate sustained VSM contractions. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Sustained vascular smooth muscle contraction is mediated by extracellular Ca(2+) influx through L-type voltage-gated Ca(2+) channels (VGCC) and RhoA/Rho-associated kinase (ROCK)-dependent Ca(2+) sensitization of the contractile machinery. VGCC activation can also trigger an ion-independent metabotropic pathway that involves G-protein/phospholipase C activation, inositol 1,4,5-trisphosphate synthesis, and Ca(2+) release from the sarcoplasmic reticulum (calcium channel-induced Ca(2+) release). We have studied the functional role of calcium channel-induced Ca(2+) release and the inter-relations between Ca(2+) channel and RhoA/ROCK activation. We have used normal and genetically modified animals to study single myocyte electrophysiology and fluorimetry as well as cytosolic Ca(2+) and diameter in intact arteries. These analyses were complemented with measurement of tension and RhoA activity in normal and reversibly permeabilized arterial rings. We have found that, unexpectedly, L-type Ca(2+) channel activation and subsequent metabotropic Ca(2+) release from sarcoplasmic reticulum participate in depolarization-evoked RhoA/ROCK activity and sustained arterial contraction. We show that these phenomena do not depend on the change in the membrane potential itself, or the mere release of Ca(2+) from the sarcoplasmic reticulum, but they require the simultaneous activation of VGCC and the downstream metabotropic pathway with concomitant Ca(2+) release. During protracted depolarizations, refilling of the stores by a residual extracellular Ca(2+) influx through VGCC helps maintaining RhoA activity and sustained arterial contraction. These findings reveal that calcium channel-induced Ca(2+) release has a major role in tonic vascular smooth muscle contractility because it links membrane depolarization and Ca(2+) channel activation with metabotropic Ca(2+) release and sensitization (RhoA/ROCK stimulation).
    Preview · Article · May 2011 · Circulation Research
Show more