33,299 research outputs found

    α<sub>1L</sub>-adrenoceptors mediate contraction of human erectile tissue

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    α1-adrenoceptor antagonists can impact upon sexual function and have potential in the treatment of erectile dysfunction. Human erectile tissue contains predominantly α1A-adrenoceptors, and here we examined whether contractions of this tissue are mediated by the functional phenotype, the α1L-adrenoceptor. Functional experiments using subtype selective agonists and antagonists, along with radioligand ([3H]tamsulosin) binding assays, were used to determine the α1-adrenoceptor population. A61603, a α1A-adrenoceptor agonist, was a full agonist with a potency 21-fold greater than that of noradrenaline. The α1A- and α1D-adrenoceptor antagonist tamsulosin antagonized noradrenaline responses with high affinity (pKD = 9.7 ± 0.3), whilst BMY7378 (100 nM) (α1D-adrenoceptor antagonist) failed to antagonize responses. In contrast, relatively low affinity estimates were obtained for both prazosin (pKD = 8.2 ± 0.1) and RS17053 (pKD = 6.9 ± 0.2), antagonists which discriminate between the α1A- and α1L-adrenoceptors. [3H]Tamsulosin bound with high affinity to the receptors of human erectile tissue (pKD = 10.3 ± 0.1) with a receptor density of 28.1 ± 1.4 fmol mg−1 protein. Prazosin displacement of [3H]tamsulosin binding revealed a single homogenous population of binding sites with a relatively low affinity for prazosin (pKi = 8.9). Taken together these data confirm that the receptor mediating contraction in human erectile tissue has the pharmacological properties of the α1L-adrenoceptor. Keywords: Erectile tissue, α1-adrenoceptor subtypes, α1L-adrenoceptor, Tamsulosin, Prazosi

    α1D-Adrenoceptors are responsible for the high sensitivity and the slow time-course of noradrenaline-mediated contraction in conductance arteries

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    The objective of this study was to determine whether the different time-course characteristics of α1-adrenoceptor-mediated contraction in arteries can be related to the subtypes involved. Contractile responses to noradrenaline (NA) were compared with inositol phosphate accumulation and extracellular signal-regulated kinase (ERK)1/2 phosphorylation after α1-agonist stimuli in the same vessels in the presence or absence of α1-antagonists in rat or in α1-subtype knockout (KO) mice. Aorta, where α1D-AR is the main functional subtype, had higher sensitivity to NA (in respect of inositol phosphate [IP], pERK1/2, and contractile response) than tail artery, where the α1A-adrenoceptor subtype is predominant. Furthermore, the contraction in aorta exhibited a slower decay after agonist removal and this was consistent in all strains harboring α1D-adrenoceptors (from rat, α1B-KO, and wild-type [WT] mice) but was not observed in the absence of the α1D-adrenoceptor signal (α1D-adrenoceptor blocked rat aorta or aorta from α1D-KO). IP formation paralleled α1-adrenoceptor-mediated contraction (agonist present or postagonist) in aorta and tail artery. High sensitivity to agonist and persistence of response after agonist removal is a property of α1D-adrenoceptors. Therefore, the preponderance of this subtype in noninnervated conductance arteries such as aorta allows responsiveness to circulating catecholamines and prevents abrupt changes in vessel caliber when the stimulus fluctuates. Conversely, in innervated distributing arteries, high local concentrations of NA are required to activate α1A-adrenoceptors for a response that is rapid but short lived allowing fine adjustment of the contractile tone by perivascular sympathetic nerves

    The role of dimerisation in the cellular trafficking of G-protein-coupled receptors

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    The concept that G-protein-coupled receptors can exist as homomeric and/or heteromeric complexes is now well established. Despite this, how dynamic such interactions are and if this may be modulated during receptor trafficking remain topics of debate. Use of endoplasmic reticulum trapping strategies and the generation of asymmetric homomers have started to provide information on the contribution of protein–protein interactions to receptor maturation, cell surface delivery and ligand-mediated endocytosis. Although dimer/oligomer formation appears to be essential for cell surface delivery of class A and class C GPCRs, this may not be the case for class B receptors

    Electrophysiological effects of 5-hydroxytryptamine on isolated human atrial myocytes, and the influence of chronic beta-adrenoceptor blockade

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    &lt;b&gt;1.&lt;/b&gt; 5-Hydroxytryptamine (5-HT) has been postulated to play a proarrhythmic role in the human atria via stimulation of 5-HT&lt;sub&gt;4&lt;/sub&gt; receptors. &lt;b&gt;2.&lt;/b&gt; The aims of this study were to examine the effects of 5-HT on the L-type Ca&lt;sup&gt;2+&lt;/sup&gt; current (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt;) action potential duration (APD), the effective refractory period (ERP) and arrhythmic activity in human atrial cells, and to assess the effects of prior treatment with &#946;-adrenoceptor antagonists. &lt;b&gt;3.&lt;/b&gt; Isolated myocytes, from the right atrial appendage of 27 consenting patients undergoing cardiac surgery who were in sinus rhythm, were studied using the whole-cell perforated patch-clamp technique at 37&#186;C. &lt;b&gt;4.&lt;/b&gt; 5-HT (1 n-10 &#956;M) caused a concentration-dependent increase in &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt;, which was potentiated in cells from &#946;-blocked (maximum response to 5-HT, E&lt;sub&gt;max&lt;/sub&gt;=299&#177;12% increase above control) compared to non-&#946;-blocked patients (E&lt;sub&gt;max&lt;/sub&gt;=220&#177;6%, P&#60;0.05), but with no change in either the potency (log EC&lt;sub&gt;50&lt;/sub&gt;: -7.09&#177;0.07 vs -7.26&#177;0.06) or Hill coefficient (&lt;i&gt;n&lt;/i&gt;&lt;sub&gt;H&lt;/sub&gt;: 1.5&#177;0.6 vs 1.5&#177;0.3) of the 5-HT concentration-response curve. &lt;b&gt;5.&lt;/b&gt; 5-HT (10 &#956;M) produced a greater increase in the APD at 50% repolarisation (APD50) in cells from &#946;-blocked patients (of 37&#177;10 ms, i.e. 589&#177;197%) vs non-&#946;-blocked patients (of 10&#177;4 ms, i.e. 157&#177;54%; P&#60;0.05). Both the APD&lt;sub&gt;90&lt;/sub&gt; and the ERP were unaffected by 5-HT. &lt;b&gt;6.&lt;/b&gt; Arrhythmic activity was observed in response to 5-HT in five of 17 cells (29%) studied from &#946;-blocked, compared to zero of 16 cells from the non-&#946;-blocked patients (P&#60;0.05). &lt;b&gt;7.&lt;/b&gt; In summary, the 5-HT-induced increase in calcium current was associated with a prolonged early plateau phase of repolarisation, but not late repolarisation or refractoriness, and the enhancement of these effects by chronic &#946;-adrenoceptor blockade was associated with arrhythmic potential

    Electrophysiological and arrhythmogenic effects of 5-hydroxytryptamine on human atrial cells are reduced in atrial fibrillation

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    5-Hydroxytryptamine (5-HT) is proarrhythmic in atrial cells from patients in sinus rhythm (SR) via activation of 5-HT&lt;sub&gt;4&lt;/sub&gt; receptors, but its effects in atrial cells from patients with atrial fibrillation (AF) are unknown. The whole-cell perforated patch-clamp technique was used to record L-type Ca&lt;sup&gt;2+&lt;/sup&gt; current (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt;), action potential duration (APD) and arrhythmic activity at 37 °C in enzymatically isolated atrial cells obtained from patients undergoing cardiac surgery, in SR or with chronic AF. In the AF group, 5-HT (10 μM) produced an increase in &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt; of 115 ± 21% above control (&lt;i&gt;n&lt;/i&gt; = 10 cells, 6 patients) that was significantly smaller than that in the SR group (232 ± 33%; &lt;i&gt;p&lt;/i&gt; 0.05; &lt;i&gt;n&lt;/i&gt; = 27 cells, 12 patients). Subsequent co-application of isoproterenol (1 μM) caused a further increase in &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt; in the AF group (by 256 ± 94%) that was greater than that in the SR group (22 ± 6%; p &#60; 0.05). The APD at 50% repolarisation (APD&lt;sub&gt;50&lt;/sub&gt;) was prolonged by 14 ± 3 ms by 5-HT in the AF group (&lt;i&gt;n&lt;/i&gt; = 37 cells, 14 patients). This was less than that in the SR group (27 ± 4 ms; &lt;i&gt;p&lt;/i&gt; &#60; 0.05; &lt;i&gt;n&lt;/i&gt; = 58 cells, 24 patients). Arrhythmic activity in response to 5-HT was observed in 22% of cells in the SR group, but none was observed in the AF group (p &#60; 0.05). Atrial fibrillation was associated with reduced effects of 5-HT, but not of isoproterenol, on &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt; in human atrial cells. This reduced effect on &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;CaL&lt;/sub&gt; was associated with a reduced APD&lt;sub&gt;50&lt;/sub&gt; and arrhythmic activity with 5-HT. Thus, the potentially arrhythmogenic influence of 5-HT may be suppressed in AF-remodelled human atrium

    A selective alpha1D-adrenoreceptor antagonist inhibits human prostate cancer cell proliferation and motility "in vitro"

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    The progression of prostate cancer (PC) to a metastatic hormone refractory disease is the major contributor to the overall cancer mortality in men, mainly because the conventional therapies are generally ineffective at this stage. Thus, other therapeutic options are needed as alternatives or in addition to the classic approaches to prevent or delay tumor progression. Catecholamines participate to the control of prostate cell functions by the activation of alpha1-adrenoreceptors (alpha1-AR) and increased sympathetic activity has been linked to PC development and evolution. Molecular and pharmacological studies identified three alpha1-AR subtypes (A, B and D), which differ in tissue distribution, cell signaling, pharmacology and physiological role. Within the prostate, alpha1A-ARs mainly control stromal cell functions, while alpha1B- and alpha1D- subtypes seem to modulate glandular epithelial cell growth. The possible direct contribution of alpha1D-ARs in tumor biology is supported by their overexpression in PC. The studies here presented investigate the "in vitro" antitumor action of A175, a selective alpha1D-AR antagonist we have recently obtained by modifying the potent, but not subtype-selective alpha1-AR antagonist (S)-WB4101, in the hormone-refractory PC3 and DU145 PC cell lines. The results indicate that A175 has an alpha1D-AR-mediated significant and dose-dependent antiproliferative action that possibly involves the induction of G0/G1 cell cycle arrest, but not apoptosis. In addition, A175 reduces cell migration and adhesiveness to culture plates. In conclusion, our work clarified some cellular aspects promoted by alpha1D-AR activity modulation and supports a further pharmacological approach in the cure of hormone-refractory PC, by targeting specifically this AR subtype

    Coupling of alpha(1)-Adrenoceptors to ERK1/2 in the Human Prostate

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    Introduction: alpha(1)-Adrenoceptors are considered critical for the regulation of prostatic smooth muscle tone. However, previous studies suggested further alpha(1)-adrenoceptor functions besides contraction. Here, we investigated whether alpha(1)-adrenoceptors in the human prostate may activate extracellular signal-regulated kinases (ERK1/2). Methods: Prostate tissues from patients undergoing radical prostatectomy were stimulated in vitro. Activation of ERK1/2 was assessed by Western blot analysis. Expression of ERK1/2 was studied by immunohistochemistry. The effect of ERK1/2 inhibition by U0126 on phenylephrine-induced contraction was studied in organ-bath experiments. Results: Stimulation of human prostate tissue with noradrenaline (30 mu M) or phenylephrine (10 mu M) resulted in ERK activation. This was reflected by increased levels of phosphorylated ERK1/2. Expression of ERK1/2 in the prostate was observed in smooth muscle cells. Incubation of prostate tissue with U0126 (30 mu M) resulted in ERK1/2 inhibition. Dose-dependent phenylephrine-induced contraction of prostate tissue was not modulated by U0126. Conclusions: alpha(1)-Adrenoceptors in the human prostate are coupled to ERK1/2. This may partially explain previous observations suggesting a role of alpha(1)-adrenoceptors in the regulation of prostate growth. Copyright (C) 2011 S. Karger AG, Base
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