Contraction Of Canine Basilar Artery Research Articles

20-Hydroxyeicosatetraenoic acid potentiates stretch-induced contraction of canine basilar artery via PKC alpha-mediated inhibition of KCa channel.

1. The present study was undertaken to elucidate whether PKCalpha plays a role in the mechanism of the stretch-induced contraction potentiated by 20-hydroxyeicosatetraenoic acid (20-HETE). The effects of 20-HETE on the canine basilar artery were compared with those of iberiotoxin, a blocker of large conductance Ca(2+)-activated K(+) channels (K(Ca) channels), as this blocker was shown earlier to sensitize these arteries to mechanical stretch. 2. Slow stretch at rates of 0.1 to 3 mm s(-1) did not produce any contraction in normal physiological solution. 3. In the presence of 20-HETE, the slow stretch could produce contraction, which was inhibited by nicardipine, a 1,4-dihydropyridine Ca(2+) channel blocker, and gadolinium, a blocker of stretch-activated cation channels. 4. 20-HETE inhibited whole-cell K(+) current and depolarized the membrane by approximately 10 mV. These effects of 20-HETE were similar to those of iberiotoxin. 5. Calphostin C, an inhibitor of protein kinase C (PKC), inhibited the action of 20-HETE, but not that of iberiotoxin. 6. In response to 20-HETE PKCalpha isoform was translocated from the cytosol to the membrane fraction, which translocation was inhibited by calphostin C. 7. These results suggest that 20-HETE induced sensitization of the canine basilar artery to stretch was caused by PKCalpha-mediated inhibition of K(Ca) channel activity.

Involvement of different activator Ca(2+) in the rate-dependent stretch-induced contractions of canine basilar artery.

Stretch evoked a contraction in a rate-dependent manner in canine basilar artery; slow stretch at rates less than 3 mm/s produced no active tension, whereas quick stretch at rates over 5 mm/s did. Large conductance Ca(2+)-activated K(+) channel blockers, including charybdotoxin, iberiotoxin, and tetraethylammonium (TEA) sensitized the basilar artery to mechanical stimulation. TEA shifted the stretch rate-tension relationship toward the left. Thus, in the presence of TEA, the slow stretch (0.1-3 mm/s) could increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and active tension. The contraction in response to slow stretch (1 mm/s) was abolished by nicardipine and Gd(3+). Quick stretch (100 mm/s) increased [Ca(2+)](i) and active tension, both of which were partially inhibited by nicardipine or Gd(3+). The Gd(3+)-insensitive component of quick stretch-induced contraction was eliminated by thapsigargin, but not by nicardipine. Ryanodine, cyclopiazonic acid, thapsigargin, U-73122, and calphostin C also abolished the nicardipine-insensitive component of quick stretch-induced contraction. These results suggest that the slow stretch-induced contraction was exclusively dependent on the Ca(2+) influx through L-type voltage-dependent Ca(2+) channels (VDCs), whereas the quick stretch-induced contraction was dependent on Ca(2+) release from sarcoplasmic reticulum (SR) and Ca(2+) influx through L-type VDCs.

Hydrogen peroxide induces contraction and raises [Ca2+]i in canine cerebral arterial smooth muscle: participation of cellular signaling pathways.

The effects of hydrogen peroxide (H2O2) on isolated canine basilar arteries, and single smooth muscle cells isolated from these arteries, were investigated in the present study. Exposure of isolated endothelium-intact and denuded arterial rings to H2O2, at concentrations of 2.2x10(-5) M to 4.4x10(-3) M, produced concentration-dependent contractile responses. Removal of the endothelium attenuated, but did not eliminate the contractions. H2O2-induced contractions were inhibited, to different degrees, by preincubation of the vessels with low concentrations of staurosporine or bisindolylmaleimide I HCl [antagonists of protein kinase C (PKC)], Gö6976 (a PKCalpha and PKCbeta1 selective antagonist), genistein (an antagonist of protein tyrosine kinase), PD-98059 (an antagonist of mitogen-activated protein kinase), wortmannin [an antagonist of phosphatidylinositol 3 (PI3)-kinases], and LY-294002 (an antagonist of PI3-kinases). These agents were also found to relax arteries precontracted by H2O2. Removal of extracellular Ca2+ or pretreatment of the vessels with 5.0 microM verapamil markedly attenuated the contractions. Complete inhibition of the contractile response was obtained after buffering intracellular Ca2+ with BAPTA-AM. A variety of specific pharmacological antagonists of several known vasoconstrictors neither inhibited nor attenuated the H2O2-induced contractions. Exposure of smooth muscle cells to H2O2 (4.4x10(-6) M to 4.4x10(-4) M) significantly raised intracellular Ca2+ ([Ca2+]i) within 20 s. This was abolished in the absence of extracellular Ca2+ or after application of 5.0 microM verapamil. Pretreatment of the cells with low concentrations of staurosporine, bisindolylmaleimide I, Gö6976, genistein, PD-98059, wortmannin, and LY-294002 markedly suppressed the H2O2-mediated [Ca2+]i elevation. The present findings suggest that hydrogen peroxide, in vitro, produces endothelium-dependent and independent contractions of canine basilar arteries, which are clearly Ca2+-dependent and are not associated with release of endogenous vasoconstrictors. Several intracellular signal transduction systems, such as PKC (both Ca2+-dependent and Ca2+-independent), protein tyrosine phosphorylation, IP3, mitogen-activated protein kinase and PI3 kinase appear to play a role in the H2O2-induced contractions in cerebral arterial muscle.

Stretching releases Ca2+ from intracellular storage sites in canine cerebral arteries

Mechanical stretch applied to canine cerebral artery produced myogenic contraction. The contraction of the artery in response to quick stretch was dependent on not only the transmembrane influx of Ca2+ through 1,4-dihydropyridine-sensitive Ca2+ channels but also the release of Ca2+ from intracellular storage sites: the stretch-produced contractile component that was resistant to 0.1 microM nicardipine, a Ca(2+)-channel antagonist, was inhibited by about 50% after treatment with ryanodine, and was almost completely suppressed by 0.1 mM 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, a putative phospholipase C inhibitor, or by lowering the temperature from 35 to 20 degrees C. The results suggest that in addition to transmembrane influx of Ca2+ through L-type Ca2+ channels, the release of Ca2+ from both ryanodine-sensitive and -insensitive intracellular storage sites, which increases intracellular Ca2+, accounts for the stretch-induced contraction of canine basilar artery. It seems also possible that inositol 1,4,5-trisphosphate is a common mediator for the release of Ca2+ from both types of intracellular storage sites.

Superoxide anion is an endothelium-derived contracting factor

The calcium ionophore A23187 causes endothelium-dependent contractions in canine basilar arteries. Removal of the endothelium, or treatment with indomethacin or superoxide dismutase (SOD), prevented the endothelium-dependent excitatory effect of the calcium ionophore. Catalase and deferoxamine were without effect. Superoxide anion generated by xanthine plus xanthine oxidase in the presence of catalase caused contractions of the vascular smooth muscle, which were abolished by SOD or heat inactivation of xanthine oxidase. The A23187-induced production of prostaglandins F2 alpha and E2 and thromboxane B2 was abolished by the removal of endothelium and by treatment with indomethacin but was not affected by the presence of SOD plus catalase. These observations are consistent with the hypothesis that superoxide anion, rather than prostaglandins generated by hydroperoxidase activity of cyclooxygenase, is an endothelium-derived contracting factor in canine cerebral arteries.

The role of endothelin in the pathogenesis of vasospasm following subarachnoid haemorrhage

The purpose of the present study was to evaluate the vasocontractile activity of endothelin, a newly isolated endothelium-derived constrictor peptide, in canine basilar arteries in vitro and in vivo. Endothelin at concentrations of 10(-12) M approximately 3 X 10(-8) M elicited dose-dependent contractions of canine basilar arteries in vitro. The maximum tension was larger than that induced by 40 mM KCl. The EC50 value was 1.9 +/- 0.6 X 10(-9) M (mean +/- SEM). The endothelin-induced contraction was reversed by 10(-8) M nicardipine or 10(-5) M approximately 10(-4) M papaverine. An intracisternal injection of 0.6 approximately 1.2 X 10(-12) mol/kg of endothelin caused biphasic contraction of the basilar artery lasting for more than 24 h. The initial phase of the contraction accompanied remarkable changes in vital signs such as an acute rise of blood pressure, bradycardia and respiratory arrest. An intracisternal injection of 2.0 X 10(-12) mol/kg of endothelin also induced acute contraction of the basilar artery. However, all of the dogs which received an intracisternal injection of 2.0 X 10(-12) mol/kg of endothelin died from sustained respiratory insufficiency. The present results demonstrate that endothelin induces strong and long-lasting contractions of cerebral arteries. Therefore, endothelin may play an important role in the pathogenesis of vasospasm.

Role of endothelium in hypoxic contraction of canine basilar artery.

1. Reversible contraction of canine basilar artery, produced by hypoxia, persisted after mechanical and chemical removal of the endothelium. The removal of endothelium was confirmed by scanning electron microscopy as well as by the abolition or reversal of the relaxant response to acetylcholine or arginine8-vasopressin. 2. Hydroquinone, believed to block selectively endothelium-mediated relaxation, also preferentially attenuated hypoxic contractions even in the absence of endothelium but did not reduce responses to 5-hydroxytryptamine (5-HT) or high external potassium. 3. Contractions induced by red blood cell haemolysate, which occur independently of the endothelium, were also selectively attenuated by hydroquinone. 4. Contractions caused by hypoxia were inhibited by pretreatment with adenosine or by its application after contraction had developed. 5. Hypoxic contraction in canine basilar artery may result partly from a direct effect on smooth muscle as well as through the endothelium. 6. Hydroquinone may have an additional locus of action in smooth muscle cells besides its well known effect on the endothelium.

Pharmacological Effect of Endothelin, an Endothelium-derived Vasoconstrictive Peptide, on Canine Basilar Arteries

The purpose of this study was to evaluate the constrictive effect of endothelin, a peptide vasoconstrictor derived from endothelium, on canine basilar artery. Constriction was measured by an isometric tension recording method. Endothelin induced prolonged contraction of canine basilar artery in a dose-dependent fashion, the estimated concentration at 50% contraction being (2.1 +/- 0.5) X 10(-9) M (mean +/- SEM). Removal of endothelium significantly augmented the arterial response to endothelin. In Ca(++)-free medium no contractile response was elicited at 10(-8) M endothelin. Papaverine (10(-4) M) and nicardipine (10(-8) M), a calcium channel blocker, almost completely inhibited the contraction induced by 10(-8) M endothelin. Pretreatment with nicardipine (10(-8) - 10(-6) M) also significantly suppressed the response to endothelin. Acetylcholine (10(-7) - 10(-4) M), adenosine triphosphate (10(-7) - 10(-5) M), and thrombin (0.1 and 1.0 U/ml) dose-dependently inhibited contraction of canine basilar artery in response to 3 X 10(-9) M endothelin. These results show that endothelin has a potent constrictive effect on canine basilar artery and suggest that this substance may play an important role in the pathogenesis of vasospasm following subarachnoid hemorrhage.

2-[125Iodo]LSD, a new ligand for the characterisation and localisation of 5-HT2 receptors.

LSD was iodinated with Na125I and chloramine T, to get the radioligand [125I]LSD ( 125IOL ) and with N-I-succinimide to obtain the nonradioactive compound 2-I-LSD (IOL) for comparative pharmacological studies. The introduction of iodine in position 2 of LSD leads to an increase in selectivity for 5HT2 receptors. In rat cortex membranes, 125IOL possesses a KD = 0.9 +/- 0.1 nmol/l, Bmax = 240 +/- 20 fmoles/mg, and a nonspecific binding of 30-40% in presence of 100 nmol/l ketanserin. In competition experiments, 5HT antagonists showed monophasic displacement curves. Their KI-values correlate well with pD'2-values for inhibition of 5HT-induced contraction of canine basilar artery. It can be concluded that the sites labelled by 125IOL have pharmacological properties in common with central 5HT2 receptors, which are identical with vascular postjunctional 5HT receptors. The high specific radioactivity of 125IOL permits detection of even small 5HT2 receptor densities which exist in the guinea pig ileum. These 125IOL binding sites are pharmacologically different to those found in the brain or on the vessels and might be a special subpopulation of 5HT2 sites. For example, ketanserin has a high affinity to the sites labelled by 125IOL in the brain and a 100 times lower affinity to the sites labelled in the ileum. In a routine binding screen with various ligands, the inhibition constants of IOL for alpha 1, alpha 2, beta, histamine and muscarinic receptors are greater than 100 nmol/l with the exception for dopamine receptors, 40 nmol/l. 125IOL was employed for the autoradiographic localisation of its binding sites after in vitro labelling of microtome rat brain sections. 125IOL labelled 5HT2 sites in the cortex and dopamine receptors in the nucleus caudatus. The exposure times required were very short, compared to those of other 5HT2 ligands available.

Serotonin-induced contraction of canine basilar artery: mediation by 5-HT 1 receptors

Serotonin and related agonists cause a marked contraction of canine basilar artery segments. These contractions can be inhibited by a variety of serotonergic antagonists. Absolute potencies of both serotonin agonists and antagonists in chamber contraction studies significantly correlate ( P < 0.01) with their potencies for 5-HT 1, but not 5-HT 2, receptors as defined by central nervous system radioligand binding studies. Serotonin-induced contractions of canine basilar artery segments appear to be mediated by 5-HT 1 receptors.