Effects of dexmedetomidine on porcine pulmonary artery vascular smooth muscle

Background: The α 2 -receptor agonist dexmedetomidine (Dex) has been shown to produce sedative and analgesic effects not only with systemic administration but also when administered in the extradural space and around peripheral nerves. The effects and mechanism of action of Dex on pulmonary arteries, however, have not been determined. This study therefore aimed to investigate the effect of Dex on pulmonary arterial vascular smooth muscle by evaluating changes in isometric contraction tension. We then attempted to determine the effects of Dex on depolarization stimulation and receptor stimulation. Methods: Endothelium-denuded porcine pulmonary arteries were sliced into 2- to 3-mm rings. We then exposed them to certain substances at various concentrations under different conditions of baseline stimulation (with KCl, adrenaline, caffeine, or histamine) and to α 2 -receptor stimulants or antagonists, or α 1 -receptor antagonists (imidazoline, yohimbine, rauwolscine, prazosin), and different conditions of Ca 2+ depletion of the intracellular reservoir or extracellular stores. We measured the changes in isometric contraction tension with each addition or change in conditions. Results: Dex enhanced the contraction induced by high-concentration KCl stimulation. Dex-induced enhancement of contraction induced by high-concentration KCl was completely suppressed by yohimbine and rauwolscine, which are α 2 -receptor antagonists, but not by prazosin. Dex, imidazoline, yohimbine, and rauwolscine reduced the increases in contraction tension induced by the receptor stimulant adrenaline. Dex suppressed the adrenaline-induced increases in contraction tension after depletion of the Ca 2+ reservoir. In the absence of extracellular Ca 2+ , Dex suppressed the adrenaline- and histamine-induced increases in contraction tension but did not affect caffeine-induced increases. Conclusions: Dex-enhanced, high-concentration KCl-induced contraction was mediated by α 2 -receptors. Adrenaline-induced contraction was suppressed by the α 2 -receptor stimulant Dex and α 2 -receptor antagonists yohimbine and rauwolscine, suggesting that the effect of Dex on adrenaline-induced contraction is attributable to its α 2 -receptor-blocking action. Dex inhibited receptor-activated Ca 2+ channels and phosphatidylinositol-1,4,5-triphosphate-induced Ca 2+ release but not Ca 2+ -induced Ca 2+ release.

Effects of dexmedetomidine on porcine pulmonary artery vascular smooth muscle

Background The α2-receptor agonist dexmedetomidine (Dex) has been shown to produce sedative and analgesic effects not only with systemic administration but also when administered in the extradural space and around peripheral nerves. The effects and mechanism of action of Dex on pulmonary arteries, however, have not been determined. This study therefore aimed to investigate the effect of Dex on pulmonary arterial vascular smooth muscle by evaluating changes in isometric contraction tension. We then attempted to determine the effects of Dex on depolarization stimulation and receptor stimulation. Methods Endothelium-denuded porcine pulmonary arteries were sliced into 2- to 3-mm rings. We then exposed them to certain substances at various concentrations under different conditions of baseline stimulation (with KCl, adrenaline, caffeine, or histamine) and to α2-receptor stimulants or antagonists, or α1-receptor antagonists (imidazoline, yohimbine, rauwolscine, prazosin), and different conditions of Ca2+ depletion of the intracellular reservoir or extracellular stores. We measured the changes in isometric contraction tension with each addition or change in conditions. Results Dex enhanced the contraction induced by high-concentration KCl stimulation. Dex-induced enhancement of contraction induced by high-concentration KCl was completely suppressed by yohimbine and rauwolscine, which are α2-receptor antagonists, but not by prazosin. Dex, imidazoline, yohimbine, and rauwolscine reduced the increases in contraction tension induced by the receptor stimulant adrenaline. Dex suppressed the adrenaline-induced increases in contraction tension after depletion of the Ca2+ reservoir. In the absence of extracellular Ca2+, Dex suppressed the adrenaline- and histamine-induced increases in contraction tension but did not affect caffeine-induced increases. Conclusions Dex-enhanced, high-concentration KCl-induced contraction was mediated by α2-receptors. Adrenaline-induced contraction was suppressed by the α2-receptor stimulant Dex and α2-receptor antagonists yohimbine and rauwolscine, suggesting that the effect of Dex on adrenaline-induced contraction is attributable to its α2-receptor-blocking action. Dex inhibited receptor-activated Ca2+ channels and phosphatidylinositol-1,4,5-triphosphate-induced Ca2+ release but not Ca2+-induced Ca2+ release.

Effects of dexmedetomidine on porcine pulmonary artery vascular smooth muscle

Background: The α2-receptor agonists, dexmedetomidine (Dex) have been shown to produce sedative and analgesic effects not only with systemic administration but also when administered in the extradural space and around peripheral nerves. However, the effects and mechanism of action of Dex on pulmonary arteries have not been determined. This study therefore aimed to investigate the effect of Dex on pulmonary arterial vascular smooth muscle by evaluating changes in isometric contraction tension. We then attempted to determine the effects of Dex on depolarization stimulation and receptor stimulation. Methods: Endothelium-denuded porcine pulmonary arteries were sliced into 2- to 3-mm rings. We then exposed them to various substances at various concentrations under different conditions of baseline stimulation (with KCl, adrenaline, caffeine, or histamine) and of the α2-receptor stimulant or antagonists, or α1-receptor antagonist (with imidazoline, yohimbine, rauwolscine, or prazosin), and different conditions of Ca2+ depletion of the intracellular reservoir or extracellular stores, measuring the changes in isometric contraction tension with each addition or change in conditions. The concentration–response relation was determined at Dex concentrations of 10−10, 10−9, 10−8, 10−7, 10−6, 5×10−6, and 10−5 M and for other experiments at 5×10-6 M. Results: Dex enhanced the contraction induced by high KCl stimulation, with the increases reaching significance at Dex concentrations of ≥5×10-6 M. The Dex-induced enhancement of contraction induced by high KCl was completely suppressed by yohimbine and rauwolscine, which are α2-receptor antagonists, but not by prazosin. Dex, imidazoline, yohimbine and rauwolscine reduced the increases in contraction tension induced by the receptor stimulant adrenaline. Dex suppressed the adrenaline-induced increases in contraction tension after depletion of Ca2+ reservoir. In the absence of extracellular Ca2+, Dex suppressed the adrenaline- and histamine-induced increases, and did not affect caffeine-induced increases in contraction tension. Conclusions: Dex-enhanced high KCl-induced contraction was mediated by α2-receptors. Adrenaline-induced contraction was suppressed by the α2-receptor stimulant Dex and α2-receptor antagonists yohimbine and rauwolscine, suggesting that the effect of Dex on adrenaline-induced contraction is attributable to its α2-receptor-blocking action. Dex inhibited receptor-activated Ca2+ channels (RACCs) and phosphatidylinositol-1,4,5-triphosphate-induced Ca2+ release (IICR) but not Ca2+-induced Ca2+ release (CICR).

Effects of dexmedetomidine on porcine pulmonary artery vascular smooth muscle

Background Dexmedetomidine is added to local anesthetics to increase their potency and extend their duration of action, thus providing postoperative analgesia with a single administration. However, the effects and mechanism of action of dexmedetomidine on pulmonary arteries have not been determined. The aim of this study was to investigate the effect of dexmedetomidine on pulmonary artery vascular smooth muscle, evaluating changes in contraction tension. Methods Endothelium-denuded porcine pulmonary arteries were sliced into 2- to 3-mm rings. Changes in isometric contraction tension were measured with the addition of various substances at various concentrations, under different conditions of baseline stimulation (with KCl, Adrenaline, caffeine, or histamine) and different conditions of Ca2+ depletion with intracellular reservoirs or extracellular stores depleted. Results Dexmedetomidine increased the contraction tension induced by high-KCl depolarization in a concentration-dependent manner. Dexmedetomidine inhibited receptor-activated Ca2+ channels (RACCs) and phosphatidylinositol-1,4,5-triphosphate-induced Ca2+ release (IICR), but not Ca2+-induced Ca2+ release (CICR). Conclusions Dex increased the contraction tension resulting from depolarization stimulation by high KCl in a concentration-dependent manner in porcine pulmonary artery vascular smooth muscle. The enhancement of high KCl-induced contraction with Dex addition was mediated by α2 receptors. Dex suppressed increases in contraction tension induced by receptor stimulation with adrenaline, also in a concentration-dependent manner. Dex inhibited RACC and IICR, but not CICR. Elucidating the effects and mechanisms of action of Dex in the central arteries is likely to be useful as basic data for creating Dex-containing local anesthetics.

Connexin43 phosphorylation by PKC and MAPK signals VEGF-mediated gap junction internalization

Gap junctions (GJs) exhibit a complex modus of assembly and degradation to maintain balanced intercellular communication (GJIC). Several growth factors, including vascular endothelial growth factor (VEGF), have been reported to disrupt cell–cell junctions and abolish GJIC. VEGF directly stimulates VEGF-receptor tyrosine kinases on endothelial cell surfaces. Exposing primary porcine pulmonary artery endothelial cells (PAECs) to VEGF for 15 min resulted in a rapid and almost complete loss of connexin43 (Cx43) GJs at cell–cell appositions and a concomitant increase in cytoplasmic, vesicular Cx43. After prolonged incubation periods (60 min), Cx43 GJs reformed and intracellular Cx43 were restored to levels observed before treatment. GJ internalization correlated with efficient inhibition of GJIC, up to 2.8-fold increased phosphorylation of Cx43 serine residues 255, 262, 279/282, and 368, and appeared to be clathrin driven. Phosphorylation of serines 255, 262, and 279/282 was mediated by MAPK, whereas serine 368 phosphorylation was mediated by PKC. Pharmacological inhibition of both signaling pathways significantly reduced Cx43 phosphorylation and GJ internalization. Together, our results indicate that growth factors such as VEGF activate a hierarchical kinase program—including PKC and MAPK—that induces GJ internalization via phosphorylation of well-known regulatory amino acid residues located in the Cx43 C-terminal tail.