Role of PKC in the attenuation of the cGMP-mediated relaxation of skinned resistance artery smooth muscle seen in glyceryl-trinitrate-tolerant rabbit

Enhancing vascular relaxing effects of nitric oxide-donor ruthenium complexes

Ruthenium-derived complexes have emerged as new nitric oxide (NO) donors that may help circumvent the NO deficiency that impairs vasodilation. NO in vessels can be produced by the endothelial cells and/or released by NO donors. NO interacts with soluble guanylyl-cyclase to produce cGMP to activate the kinase-G pathway. As a result, conductance arteries, veins and resistance arteries dilate, whereas the cytosolic Ca2+ levels in the smooth muscle cells decrease. NO also reacts with oxygen or the superoxide anion, to generate reactive oxygen species that modulate NO-induced vasodilation. In this article, we focus on NO production by NO synthase and discuss the vascular changes taking place during hypertension originating from endothelial dysfunction. We will describe how the NO released from ruthenium-derived complexes enhances the vascular effects arising from failed NO generation or lack of NO bioavailability. In addition, how ruthenium-derived NO donors induce the hypotensive effect by vasodilation is also discussed.

Effects of chronic in vivo administration of nitroglycerine on ACh-induced endothelium-dependent relaxation in rabbit cerebral arteries

BACKGROUND AND PURPOSE

In the setting of nitrate tolerance, endothelium-dependent relaxation is reduced in several types of peripheral vessels. However, it is unknown whether chronic in vivo administration of nitroglycerine modulates such relaxation in cerebral arteries.

EXPERIMENTAL APPROACH

Isometric force and smooth muscle cell membrane potential were measured in endothelium-intact strips from rabbit middle cerebral artery (MCA) and posterior cerebral artery (PCA).

KEY RESULTS

ACh (0.1-10 microM) concentration-dependently induced endothelium-dependent relaxation during the contraction induced by histamine in both MCA and PCA. Chronic (10 days) in vivo administration of nitroglycerine reduced the ACh-induced relaxation in PCA but not in MCA, in the presence of the cyclooxygenase inhibitor diclofenac (3 microM). In the presence of the NO-synthase inhibitor N (omega)-nitro-L-arginine (L-NNA, 0.1 mM) plus diclofenac, in MCA from both nitroglycerine-untreated control and -treated rabbits, ACh (0.1-10 microM) induced a smooth muscle cell hyperpolarization and relaxation, and these were blocked by the small-conductance Ca(2+)-activated K(+)-channel inhibitor apamin (0.1 microM), but not by the large- and intermediate-conductance Ca(2+)-activated K(+)-channel inhibitor charybdotoxin (0.1 microM). In contrast, in PCA, ACh (<3 microM) induced neither hyperpolarization nor relaxation under these conditions, suggesting that the endothelium-derived relaxing factor is NO in PCA, whereas endothelium-derived hyperpolarizing factor (EDHF) plays a significant role in MCA.

CONCLUSIONS AND IMPLICATIONS

It is suggested that in rabbit cerebral arteries, the function of the endothelium-derived relaxing factor NO and that of EDHF may be modulated differently by chronic in vivo administration of nitroglycerine.

Role of protein kinase C isozymes in the regulation of alpha1-adrenergic receptor-mediated contractions in ovine uterine arteries

Previously, we demonstrated that activation of protein kinase C (PRKC) enhanced alpha(1)-adrenergic receptor-induced contractions in nonpregnant ovine uterine arteries but inhibited the contractions in pregnant ovine uterine arteries. The present study tested the hypothesis that differential regulation of PRKC isozyme activities contributes to the different effects of phorbol 12, 13-dibutyrate (PDBu) on alpha(1)-adrenergic receptor-mediated contractions between the pregnant and nonpregnant ovine uterine arteries. Phenylephrine-induced contractions of ovine nonpregnant and pregnant uterine arteries were determined in the absence or presence of the PRKC activator PDBu and/or in combination with conventional and novel PRKC isozyme inhibitor GF109203X, PRKC isozyme-selective inhibitory peptides for conventional PRKC, PRKCB1, PRKCB2, and PRKCE. GF109203X produced a concentration-dependent inhibition of phenylephrine-induced contractions in both nonpregnant and pregnant uterine arteries, and it reversed the PDBu-mediated potentiation and inhibition of phenylephrine-induced contractions in nonpregnant and pregnant uterine artieries, respectively. In addition, PRKCB1, PRKCB2, and PRKCE inhibitory peptides blocked the PDBu-mediated responses in both nonpregnant and pregnant uterine arteries. Western blot analysis showed that PDBu induced a membrane translocation of PRKCA, PRKCB1, PRKCB2, and PRKCE in pregnant uterine arteries, and PRKCB1, PRKCB2, and PRKCE in nonpregnant uterine arteries. The results disprove the hypothesis that the dichotomy of PRKC mechanisms in the regulation of alpha(1)-adrenergic receptor-induced contractions in nonpregnant and pregnant uterine arteries is caused by the activation of different PRKC isozymes, and suggest downstream mechanisms of differential subcellular distributions for the distinct functional effects of PRKC isozymes in the adaptation of uterine arteries to pregnancy.

Chronic nitroglycerine administration reduces endothelial nitric oxide production in rabbit mesenteric resistance artery

We investigated whether 10 days' in vivo treatment with nitroglycerine (NTG) would inhibit nitric oxide production by the endothelial cells of resistance arteries ex vivo and, if so, what the underlying mechanism might be. ACh increased the intracellular nitric oxide concentration ([NO]i; estimated using the nitric oxide-sensitive fluorescent dye diaminofluorescein-2) within the endothelial cells of rabbit mesenteric resistance arteries. This effect was significantly smaller in arteries isolated from NTG-treated rabbits than in those from control rabbits. The reduction in endothelial [NO]i in NTG-treated rabbits was prevented when olmesartan (blocker of type 1 angiotensin II receptors (AT1Rs)) was coadministered in vivo with NTG and also when the superoxide scavenger manganese (III) tetrakis-(4-benzoic acid) porphyrin (Mn-TBAP), the protein kinase C (PKC) inhibitor GF109203X or L-arginine (with or without the active form of folate (5-methyltetrahydrofolate)) was incubated with the arteries in vitro. Endothelial cell superoxide production (estimated by ethidium fluorescence) was greatly increased in arteries from NTG-treated rabbits. This was normalized by in vivo coadministration of olmesartan with NTG and also by in vitro application of Mn-TBAP or GF109203X (but not of 5-methyltetrahydrofolate+L-arginine). ACh increased the intracellular Ca2+ concentration (estimated using the Ca2+-sensitive dye Fura 2) within endothelial cells, the increase being not significantly different between NTG-treated rabbits and control rabbits. We conclude that in NTG-treated rabbits, endothelial nitric oxide production in mesenteric resistance arteries is reduced, possibly through a reduction in the bioavailability of L-arginine via an action mediated by superoxide. Activation of the AT1R-PKC pathway may be involved in increasing superoxide production.

Reduced hyperpolarization in endothelial cells of rabbit aortic valve following chronic nitroglycerine administration

This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the hyperpolarization induced by acetylcholine (ACh) in aortic valve endothelial cells (AVECs) of the rabbit and, if so, whether antioxidant agents can normalize this downregulated hyperpolarization. ACh (0.03-3 microM) induced a hyperpolarization through activations of both apamin- and charybdotoxin-sensitive Ca2+-activated K+ channels (K(Ca)) in rabbit AVECs. The intermediate-conductance K(Ca) channel (IK(Ca)) activator 1-ethyl-2-benzimidazolinone (1-EBIO, 0.3 mM) induced a hyperpolarization of the same magnitude as ACh (3 microM). The ACh-induced hyperpolarization was significantly weaker, although the ACh-induced [Ca2+]i increase was unchanged, in NTG-treated rabbits (versus NTG-untreated control rabbits). The hyperpolarization induced by 1-EBIO was also weaker in NTG-treated rabbits. The reduced ACh-induced hyperpolarization seen in NTG-treated rabbits was not modified by in vitro application of the superoxide scavengers Mn-TBAP, tiron or ascorbate, but it was normalized when ascorbate was coadministered with NTG in vivo. Superoxide production within the endothelial cell (estimated by ethidium fluorescence) was increased in NTG-treated rabbits and this increased production was normalized by in vivo coadministration of ascorbate with the NTG. It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced hyperpolarization in rabbit AVECs, possibly through chronic actions mediated by superoxide.

Distinct agonist responsibilities of the first and second branches of mouse mesenteric artery

The mesenteric artery (MA) is suitable for consideration as a typical micro-resistant artery for examination of arteriosclerosis. The MA is comprised of the first (MA1), second (MA2), and additional fine structural branches; however, differences in terms of responsibilities of these branches have not been assessed. The objective of this study was to differentiate contractile responses in the MAs of mice. MA2 rings (100 microm diameter, 1 mm length) displayed maximal force development (846.8 +/- 55.6 microN; n = 5) upon stimulation with 50 mM KCl under 400 microN resting tension. However, both MA1 and aorta required resting tension exceeding 600 microN. Treatment of MA2 with phenylephrine (PE; 10 microM), norepinephrine (NE; 10 microM), thromboxane A(2) (analog U46619; 100 nM), or prostaglandin F(2a) (PG; 10 microM) induced sustained contractions. Responses were 1507.8 +/- 88.8, 1543 + 5 +/- 149.6, 2088.6 +/- 151.6, and 1441.9 +/- 103.6 microN (n = 7), respectively. These values were markedly larger than those of the KCl-induced response. In MA1 and aorta, PE-induced and NE-induced responses were indistinct from the KCl response. This investigation revealed that MA1 exhibits responsibilities similar to those of the aorta, whereas MA2 possesses distinct responsibilities. MA2 might serve as a micro-resistant artery model.

Oxidative stress and Mrp2 internalization

Oxidative stress in the liver is sometimes accompanied by cholestasis. We have described the internalization of multidrug resistance-associated protein 2/ATP-binding cassette transporter family 2 (Mrp2/Abcc2), a biliary transporter involved in bile-salt-independent bile flow, under ethacrynic acid (EA)-induced acute oxidative stress in rat liver. However, the signaling pathway and regulatory molecules have not been investigated. In the present study, we investigated the mechanism of EA-induced Mrp2 internalization using isolated rat hepatocyte couplets (IRCHs). The Mrp2 index, defined as the ratio of Mrp2-positive canalicular membrane staining in IRCHs per number of cell nuclei, was significantly reduced by treatment with EA. This reduction was abolished by a nonspecific protein kinase C (PKC) inhibitor Gö6850, a Ca(2+) chelator, EGTA, but not by a protein kinase A (PKA)-selective inhibitor, a Ca(2+)-dependent conventional PKC (cPKC) inhibitor Gö6976, or a protein kinase G (PKG) inhibitor (1 microM). Moreover, an increase in the intracellular Ca(2+) level and NO release into medium were observed shortly after the EA treatment. Both of these increases, as well as Mrp2 internalization, were completely blocked by EGTA. In conclusion, EA produced a reduction in GSH, Ca(2+) elevation, NO production, and nPKC activation in a sequential manner, finally leading to Mrp2 internalization.

Characteristics of attenuated endothelium-dependent relaxation seen in rabbit intrapulmonary vein following chronic nitroglycerine administration

1 This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the endothelium-dependent relaxation induced by acetylcholine (ACh) in the rabbit intrapulmonary vein and, if so, whether the type 1 angiotensin II receptor (AT(1)R) blocker valsartan normalizes this downregulated relaxation. 2 In strips treated with the cyclooxygenase inhibitor diclofenac, ACh induced a relaxation only when the endothelium was intact. A small part of this ACh-induced relaxation was inhibited by coapplication of two Ca(2+)-activated K(+)-channel blockers (charybdotoxin (CTX)+apamin) and the greater part of the response was inhibited by the nitric-oxide-synthase inhibitor N(omega)-nitro-L-arginine (L-NNA). 3 The endothelium-dependent relaxation induced by ACh, but not the endothelium-independent relaxation induced by the nitric oxide donor NOC-7, was significantly reduced in NTG-treated rabbits (versus those in NTG-nontreated control rabbits). The attenuated relaxation was normalized by coapplication of valsartan with the NTG. 4 In the vascular wall, both the amount of localized angiotensin II and the production of superoxide anion were increased by in vivo NTG treatment. These variables were normalized by coapplication of valsartan with the NTG. 5 It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced endothelium-dependent relaxation, mainly through an inhibition of endothelial nitric oxide production in the rabbit intrapulmonary vein. A possible role for AT(1)R is proposed in the mechanism underlying this effect.