The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform

Finn Olav Levy - One of the best experts on this subject based on the ideXlab platform.

  • Heterologous desensitization is evoked by both agonist and antagonist stimulation of the human 5-HT7 serotonin receptor
    European Journal of Pharmacology, 2006
    Co-Authors: Kurt A Krobert, Kjetil Wessel Andressen, Finn Olav Levy
    Abstract:

    Previously, we demonstrated that human serotonin (5-HT) 5-HT(7) receptors display marked constitutive activity. Here, we tested if the constitutive activation of adenylyl cyclase by 5-HT(7) receptors influenced both the desensitization properties of transfected 5-HT(7) receptors and the ability of endogenous G(s)-coupled receptors to activate adenylyl cyclase. Using membranes from stably transfected HEK293 cells expressing the recombinant human 5-HT(7) receptor splice variants (5-HT(7(a)), 5-HT(7(b)) and 5-HT(7(d))), we compared the effects of 1-h or 24-h preincubation of the agonist 5-HT, partial inverse agonists Mesulergine and SB269970, and full inverse agonists clozapine and methiothepin on subsequent activation of adenylyl cyclase by both 5-HT through transfected 5-HT(7) receptors and the endogenous G(s)-coupled beta-adrenoceptors and prostaglandin receptors of HEK293 cells. The data show that stable expression of 5-HT(7) receptors is sufficient to attenuate adenylyl cyclase activation by endogenous G(s)-coupled receptors. Interestingly, preincubation with inverse agonists not only failed to result in the predicted resensitization of all receptor mediated adenylyl cyclase activation, but some inverse agonists further attenuated (desensitized) beta-adrenoceptor and prostaglandin-stimulated adenylyl cyclase activation similar to long-term agonist exposure by 5-HT. These effects were not correlated with inverse agonist efficacy, were not accompanied by receptor down-regulation and appear to be mediated by a protein kinase A (PKA) independent mechanism. It is concluded that the human 5-HT(7) receptor mediates heterologous desensitization of endogenous G(s)-coupled receptors through an unknown and potentially novel mechanism.

  • heterologous desensitization is evoked by both agonist and antagonist stimulation of the human 5 ht7 serotonin receptor
    European Journal of Pharmacology, 2006
    Co-Authors: Kurt A Krobert, Kjetil Wessel Andressen, Finn Olav Levy
    Abstract:

    Abstract Previously, we demonstrated that human serotonin (5-HT) 5-HT 7 receptors display marked constitutive activity. Here, we tested if the constitutive activation of adenylyl cyclase by 5-HT 7 receptors influenced both the desensitization properties of transfected 5-HT 7 receptors and the ability of endogenous G s -coupled receptors to activate adenylyl cyclase. Using membranes from stably transfected HEK293 cells expressing the recombinant human 5-HT 7 receptor splice variants (5-HT 7(a) , 5-HT 7(b) and 5-HT 7(d) ), we compared the effects of 1-h or 24-h preincubation of the agonist 5-HT, partial inverse agonists Mesulergine and SB269970, and full inverse agonists clozapine and methiothepin on subsequent activation of adenylyl cyclase by both 5-HT through transfected 5-HT 7 receptors and the endogenous G s -coupled β-adrenoceptors and prostaglandin receptors of HEK293 cells. The data show that stable expression of 5-HT 7 receptors is sufficient to attenuate adenylyl cyclase activation by endogenous G s -coupled receptors. Interestingly, preincubation with inverse agonists not only failed to result in the predicted resensitization of all receptor mediated adenylyl cyclase activation, but some inverse agonists further attenuated (desensitized) β-adrenoceptor and prostaglandin-stimulated adenylyl cyclase activation similar to long-term agonist exposure by 5-HT. These effects were not correlated with inverse agonist efficacy, were not accompanied by receptor down-regulation and appear to be mediated by a protein kinase A (PKA) independent mechanism. It is concluded that the human 5-HT 7 receptor mediates heterologous desensitization of endogenous G s -coupled receptors through an unknown and potentially novel mechanism.

  • the human 5 ht7 serotonin receptor splice variants constitutive activity and inverse agonist effects
    British Journal of Pharmacology, 2002
    Co-Authors: Kurt A Krobert, Finn Olav Levy
    Abstract:

    Using membranes from stably or transiently transfected HEK293 cells cultured in 5-HT-free medium and expressing the recombinant human 5-HT7 receptor splice variants (h5-HT7(a), h5-HT7(b) and h5-HT7(d)), we compared their abilities to constitutively activate adenylyl cyclase (AC). All h5-HT7 splice variants elevated basal and forskolin-stimulated AC. The basal AC activity was reduced by the 5-HT7 antagonist methiothepin and this effect was blocked by Mesulergine (neutral 5-HT7 antagonist) indicating that the inhibitory effect of methiothepin is inverse agonism at the 5-HT7 receptor. Receptor density correlated poorly with constitutive AC activity in stable clonal cell lines and transiently transfected cells. Mean constitutive AC activity as a percentage of forskolin-stimulated AC was significantly higher for the h5-HT7(b) splice variant compared to the h5-HT7(a) and h5-HT7(d) splice variants but only in stable cell lines. All eight 5-HT antagonists tested inhibited constitutive AC activity of all splice variants in a concentration-dependent manner. No differences in inverse agonist potencies (pIC50) were observed between the splice variants. The rank order of potencies was in agreement and highly correlated with antagonist potencies (pKb) determined by antagonism of 5-HT-stimulated AC activity (methiothepin>metergoline>Mesulergine⩾clozapine⩾spiperone⩾ritanserin>methysergide>ketanserin). The efficacy of inverse agonism was not receptor level dependent and varied for several 5-HT antagonists between membrane preparations of transiently and stably transfected cells. It is concluded that the h5-HT7 splice variants display similar constitutive activity and inverse agonist properties. Keywords: 5-HT7 receptor, splice variants, constitutive activity, adenylyl cyclase, inverse agonism Introduction Serotonin (5-HT) mediates its diverse physiological effects through at least 14 different receptor subtypes, of which 13 belong to the G-protein-coupled or seven transmembrane-spanning receptor family (Hoyer et al., 1994). Defined on the basis of molecular, pharmacological and functional criteria, 5-HT receptors form seven discrete families, including three subtypes positively coupled to adenylyl cyclase (5-HT4, 5-HT6 and 5-HT7) through G-proteins. Whereas many of the 5-HT receptors are encoded by a single exon, RNA editing (Burns et al., 1997) and alternative mRNA splicing of 5-HT receptor subtypes (Gerald et al., 1995; Heidmann et al., 1997) produce splice variants adding another level to receptor complexity. Three human 5-HT7 receptor splice variants (h5-HT7(a), h5-HT7(b), h5-HT7(d)) have been identified that are structurally identical except in their predicted intracellular carboxyl terminal (C-terminal) tail (Heidmann et al., 1997). Although physiological roles for 5-HT7 receptors have been implicated in multiple organ systems, such as the cardiovascular system, CNS and digestive tract (Eglen et al., 1997; Saxena et al., 1998; Vanhoenacker et al., 2000), little is known about which splice variants are mediating these effects. In support of the diverse physiological roles, RT – PCR studies indicate that 5-HT7 receptors are widely distributed and that all three splice variants can be co-localized in the same tissue (Heidmann et al., 1997; Krobert et al., 2001). Studies addressing the functional differences of the 5-HT7 receptor splice variants at the cellular and molecular levels have yielded few insights into the specific physiological roles of h5-HT7 receptor splice variants. A comparative characterization of the rat 5-HT7 receptor splice variants revealed no differences in ligand binding affinities or AC activation (Heidmann et al., 1998). We recently reported that the three h5-HT7 receptor splice variants share indistinguishable pharmacological profiles and similar abilities to stimulate AC in HEK293 cells (Krobert et al., 2001), indicating that the C-terminal tail does not influence ligand binding or receptor/G-protein coupling. Studies of other receptor splice variants highlight the numerous possible roles for the C-terminal tail that may give rise to functional diversity of h5-HT7 receptor splice variants. For example, the C-terminal tail of diverse G-protein coupled receptors is known to influence desensitization properties (Vanetti et al., 1993; Negishi et al., 1993; Rousseau et al., 1996), intracellular trafficking (Bremnes et al., 2000), receptor-effector coupling (Journot et al., 1994; Vanetti et al., 1993; Gerald et al., 1995), ligand binding (Claeysen et al., 1999; Canton et al., 1996), G-protein specificity (Namba et al., 1993), interactions with PDZ domain containing proteins (Songyang et al., 1997; Hall et al., 1998; Daviet et al., 1999) and basal constitutive activity (Prezeau et al., 1996). For the h5-HT4 receptor, with at least seven known splice variants differing only in the C-terminal tail (Bender et al., 2000), constitutive activity differs between the splice variants (Claeysen et al., 1999; 2000). The C-terminal tail appears to be critical for maintaining the 5-HT4 receptor in an inactive conformation as truncation of the C-terminal tail significantly increases constitutive activity (Claeysen et al., 1999). Despite the lack of sequence homology in 5-HT7 and 5-HT4 C-terminal tails, structural similarities exist (both contain splice variants with a truncation and one with additional phosphorylation sites (Heidmann et al., 1998)), suggesting a similar role for the C-terminal tail of 5-HT7 receptors. To date, the constitutive activation of AC by 5-HT7 receptor splice variants is poorly characterized. Thomas et al. (1998) have reported a concentration-dependent inhibition of basal AC activity to 5-HT antagonists in HEK293 cells expressing the h5-HT7(a) receptor splice variant indicating that the h5-HT7(a) is constitutively active. In HEK293 cells expressing the truncated h5-HT7(b) receptor variant, Jasper et al. (1997) did not observe constitutive activation or inverse agonism in response to the 5-HT antagonists reported by Thomas et al. (1998). In the only report comparing the three rat splice variants, no mention of the constitutive activity was reported (Heidmann et al., 1998) and currently the ability of the h5-HT7(d) splice variant to constitutively activate AC is unknown. Therefore, in the present study we investigated whether the h5-HT7 receptor splice variants expressed in HEK293 cells differ in their ability to constitutively activate AC and in their response to inverse agonists.

Kurt A Krobert - One of the best experts on this subject based on the ideXlab platform.

  • Heterologous desensitization is evoked by both agonist and antagonist stimulation of the human 5-HT7 serotonin receptor
    European Journal of Pharmacology, 2006
    Co-Authors: Kurt A Krobert, Kjetil Wessel Andressen, Finn Olav Levy
    Abstract:

    Previously, we demonstrated that human serotonin (5-HT) 5-HT(7) receptors display marked constitutive activity. Here, we tested if the constitutive activation of adenylyl cyclase by 5-HT(7) receptors influenced both the desensitization properties of transfected 5-HT(7) receptors and the ability of endogenous G(s)-coupled receptors to activate adenylyl cyclase. Using membranes from stably transfected HEK293 cells expressing the recombinant human 5-HT(7) receptor splice variants (5-HT(7(a)), 5-HT(7(b)) and 5-HT(7(d))), we compared the effects of 1-h or 24-h preincubation of the agonist 5-HT, partial inverse agonists Mesulergine and SB269970, and full inverse agonists clozapine and methiothepin on subsequent activation of adenylyl cyclase by both 5-HT through transfected 5-HT(7) receptors and the endogenous G(s)-coupled beta-adrenoceptors and prostaglandin receptors of HEK293 cells. The data show that stable expression of 5-HT(7) receptors is sufficient to attenuate adenylyl cyclase activation by endogenous G(s)-coupled receptors. Interestingly, preincubation with inverse agonists not only failed to result in the predicted resensitization of all receptor mediated adenylyl cyclase activation, but some inverse agonists further attenuated (desensitized) beta-adrenoceptor and prostaglandin-stimulated adenylyl cyclase activation similar to long-term agonist exposure by 5-HT. These effects were not correlated with inverse agonist efficacy, were not accompanied by receptor down-regulation and appear to be mediated by a protein kinase A (PKA) independent mechanism. It is concluded that the human 5-HT(7) receptor mediates heterologous desensitization of endogenous G(s)-coupled receptors through an unknown and potentially novel mechanism.

  • heterologous desensitization is evoked by both agonist and antagonist stimulation of the human 5 ht7 serotonin receptor
    European Journal of Pharmacology, 2006
    Co-Authors: Kurt A Krobert, Kjetil Wessel Andressen, Finn Olav Levy
    Abstract:

    Abstract Previously, we demonstrated that human serotonin (5-HT) 5-HT 7 receptors display marked constitutive activity. Here, we tested if the constitutive activation of adenylyl cyclase by 5-HT 7 receptors influenced both the desensitization properties of transfected 5-HT 7 receptors and the ability of endogenous G s -coupled receptors to activate adenylyl cyclase. Using membranes from stably transfected HEK293 cells expressing the recombinant human 5-HT 7 receptor splice variants (5-HT 7(a) , 5-HT 7(b) and 5-HT 7(d) ), we compared the effects of 1-h or 24-h preincubation of the agonist 5-HT, partial inverse agonists Mesulergine and SB269970, and full inverse agonists clozapine and methiothepin on subsequent activation of adenylyl cyclase by both 5-HT through transfected 5-HT 7 receptors and the endogenous G s -coupled β-adrenoceptors and prostaglandin receptors of HEK293 cells. The data show that stable expression of 5-HT 7 receptors is sufficient to attenuate adenylyl cyclase activation by endogenous G s -coupled receptors. Interestingly, preincubation with inverse agonists not only failed to result in the predicted resensitization of all receptor mediated adenylyl cyclase activation, but some inverse agonists further attenuated (desensitized) β-adrenoceptor and prostaglandin-stimulated adenylyl cyclase activation similar to long-term agonist exposure by 5-HT. These effects were not correlated with inverse agonist efficacy, were not accompanied by receptor down-regulation and appear to be mediated by a protein kinase A (PKA) independent mechanism. It is concluded that the human 5-HT 7 receptor mediates heterologous desensitization of endogenous G s -coupled receptors through an unknown and potentially novel mechanism.

  • the human 5 ht7 serotonin receptor splice variants constitutive activity and inverse agonist effects
    British Journal of Pharmacology, 2002
    Co-Authors: Kurt A Krobert, Finn Olav Levy
    Abstract:

    Using membranes from stably or transiently transfected HEK293 cells cultured in 5-HT-free medium and expressing the recombinant human 5-HT7 receptor splice variants (h5-HT7(a), h5-HT7(b) and h5-HT7(d)), we compared their abilities to constitutively activate adenylyl cyclase (AC). All h5-HT7 splice variants elevated basal and forskolin-stimulated AC. The basal AC activity was reduced by the 5-HT7 antagonist methiothepin and this effect was blocked by Mesulergine (neutral 5-HT7 antagonist) indicating that the inhibitory effect of methiothepin is inverse agonism at the 5-HT7 receptor. Receptor density correlated poorly with constitutive AC activity in stable clonal cell lines and transiently transfected cells. Mean constitutive AC activity as a percentage of forskolin-stimulated AC was significantly higher for the h5-HT7(b) splice variant compared to the h5-HT7(a) and h5-HT7(d) splice variants but only in stable cell lines. All eight 5-HT antagonists tested inhibited constitutive AC activity of all splice variants in a concentration-dependent manner. No differences in inverse agonist potencies (pIC50) were observed between the splice variants. The rank order of potencies was in agreement and highly correlated with antagonist potencies (pKb) determined by antagonism of 5-HT-stimulated AC activity (methiothepin>metergoline>Mesulergine⩾clozapine⩾spiperone⩾ritanserin>methysergide>ketanserin). The efficacy of inverse agonism was not receptor level dependent and varied for several 5-HT antagonists between membrane preparations of transiently and stably transfected cells. It is concluded that the h5-HT7 splice variants display similar constitutive activity and inverse agonist properties. Keywords: 5-HT7 receptor, splice variants, constitutive activity, adenylyl cyclase, inverse agonism Introduction Serotonin (5-HT) mediates its diverse physiological effects through at least 14 different receptor subtypes, of which 13 belong to the G-protein-coupled or seven transmembrane-spanning receptor family (Hoyer et al., 1994). Defined on the basis of molecular, pharmacological and functional criteria, 5-HT receptors form seven discrete families, including three subtypes positively coupled to adenylyl cyclase (5-HT4, 5-HT6 and 5-HT7) through G-proteins. Whereas many of the 5-HT receptors are encoded by a single exon, RNA editing (Burns et al., 1997) and alternative mRNA splicing of 5-HT receptor subtypes (Gerald et al., 1995; Heidmann et al., 1997) produce splice variants adding another level to receptor complexity. Three human 5-HT7 receptor splice variants (h5-HT7(a), h5-HT7(b), h5-HT7(d)) have been identified that are structurally identical except in their predicted intracellular carboxyl terminal (C-terminal) tail (Heidmann et al., 1997). Although physiological roles for 5-HT7 receptors have been implicated in multiple organ systems, such as the cardiovascular system, CNS and digestive tract (Eglen et al., 1997; Saxena et al., 1998; Vanhoenacker et al., 2000), little is known about which splice variants are mediating these effects. In support of the diverse physiological roles, RT – PCR studies indicate that 5-HT7 receptors are widely distributed and that all three splice variants can be co-localized in the same tissue (Heidmann et al., 1997; Krobert et al., 2001). Studies addressing the functional differences of the 5-HT7 receptor splice variants at the cellular and molecular levels have yielded few insights into the specific physiological roles of h5-HT7 receptor splice variants. A comparative characterization of the rat 5-HT7 receptor splice variants revealed no differences in ligand binding affinities or AC activation (Heidmann et al., 1998). We recently reported that the three h5-HT7 receptor splice variants share indistinguishable pharmacological profiles and similar abilities to stimulate AC in HEK293 cells (Krobert et al., 2001), indicating that the C-terminal tail does not influence ligand binding or receptor/G-protein coupling. Studies of other receptor splice variants highlight the numerous possible roles for the C-terminal tail that may give rise to functional diversity of h5-HT7 receptor splice variants. For example, the C-terminal tail of diverse G-protein coupled receptors is known to influence desensitization properties (Vanetti et al., 1993; Negishi et al., 1993; Rousseau et al., 1996), intracellular trafficking (Bremnes et al., 2000), receptor-effector coupling (Journot et al., 1994; Vanetti et al., 1993; Gerald et al., 1995), ligand binding (Claeysen et al., 1999; Canton et al., 1996), G-protein specificity (Namba et al., 1993), interactions with PDZ domain containing proteins (Songyang et al., 1997; Hall et al., 1998; Daviet et al., 1999) and basal constitutive activity (Prezeau et al., 1996). For the h5-HT4 receptor, with at least seven known splice variants differing only in the C-terminal tail (Bender et al., 2000), constitutive activity differs between the splice variants (Claeysen et al., 1999; 2000). The C-terminal tail appears to be critical for maintaining the 5-HT4 receptor in an inactive conformation as truncation of the C-terminal tail significantly increases constitutive activity (Claeysen et al., 1999). Despite the lack of sequence homology in 5-HT7 and 5-HT4 C-terminal tails, structural similarities exist (both contain splice variants with a truncation and one with additional phosphorylation sites (Heidmann et al., 1998)), suggesting a similar role for the C-terminal tail of 5-HT7 receptors. To date, the constitutive activation of AC by 5-HT7 receptor splice variants is poorly characterized. Thomas et al. (1998) have reported a concentration-dependent inhibition of basal AC activity to 5-HT antagonists in HEK293 cells expressing the h5-HT7(a) receptor splice variant indicating that the h5-HT7(a) is constitutively active. In HEK293 cells expressing the truncated h5-HT7(b) receptor variant, Jasper et al. (1997) did not observe constitutive activation or inverse agonism in response to the 5-HT antagonists reported by Thomas et al. (1998). In the only report comparing the three rat splice variants, no mention of the constitutive activity was reported (Heidmann et al., 1998) and currently the ability of the h5-HT7(d) splice variant to constitutively activate AC is unknown. Therefore, in the present study we investigated whether the h5-HT7 receptor splice variants expressed in HEK293 cells differ in their ability to constitutively activate AC and in their response to inverse agonists.

Pieter Janssen - One of the best experts on this subject based on the ideXlab platform.

  • smooth muscle 5 ht2a receptors mediating contraction of porcine isolated proximal stomach strips
    British Journal of Pharmacology, 2002
    Co-Authors: Pieter Janssen, Nh Prins, Ann Meulemans, Romain Lefebvre
    Abstract:

    The aim of this study was to characterize the 5-HT receptors involved in the 5-HT-induced contraction of longitudinal muscle (LM) strips of porcine proximal stomach. This was done in a classical organ bath set-up for isotonic measurement. The concentration-contraction curve to 5-HT was not modified by 5-HT3 and 5-HT4 receptor antagonism. Methysergide, ketanserin and Mesulergine antagonized the curve to 5-HT. Concomitantly, increasing concentrations of ketanserin and Mesulergine progressively revealed a biphasic nature of the 5-HT curve. Ketanserin antagonized the low-affinity receptor while it did not modify the high-affinity receptor. Tetrodotoxin did not influence the concentration-contraction curve to 5-HT neither in the absence nor presence of ketanserin, indicating that nerves are not involved. Ketanserin competitively antagonized the monophasic concentration-response curve to α-Methyl-5-HT, yielding a Schild slope that was not significantly different from unity. After constraining the Schild slope to unity, a pKB estimate of 8.23±0.90 was obtained. This affinity estimate of ketanserin closely approximates previously reported affinities at 5-HT2A receptors. In the presence of ketanserin (0.1 μM; exposing the high-affinity receptor), a wide range of 5-HT receptor antagonists covering all 5-HT receptors known, was tested. Only methysergide and ritanserin inhibited the response to 5-HT, thus expressing affinity for the high-affinity receptor. This did not reveal the identity of the receptor involved. It can be concluded that 5-HT induces pig proximal stomach (LM) contraction via 5-HT2A receptors located on smooth muscle. A ketanserin-insensitive phase of contractions could not be characterized between the actually known classes of 5-HT receptors with the pharmacological tools that were used. British Journal of Pharmacology (2002) 137, 1217–1224. doi:10.1038/sj.bjp.0704992

  • pharmacological characterization of the 5 ht receptors mediating contraction and relaxation of canine isolated proximal stomach smooth muscle
    British Journal of Pharmacology, 2002
    Co-Authors: Pieter Janssen, Nh Prins, Al Meulemans, Romain Lefebvre
    Abstract:

    We aimed to characterize 5-HT receptors mediating contraction and relaxation to 5-HT in dog proximal stomach longitudinal muscle (LM) strips. Of the tryptamine analogues tested, 5-HT was the most potent contractile agent at basal length, while 5-CT was the most potent relaxant of PGF2α-induced contraction. Neither the contractions to 5-HT, nor the relaxations to 5-CT were influenced by tetrodotoxin, illustrating that action potential propagation is not involved. The 5-HT-induced contraction was antagonized by Mesulergine (0.03 to 0.3 μM) and ketanserin (2–20 nM), but the antagonism was not of a simple competitive nature, indicating multiple receptor involvement. Ketanserin (3 to 30 nM) and Mesulergine (30 nM) competitively antagonized the α-Me-5-HT-induced contraction (pKB: 8.83±0.09 and pA2: 8.25±0.06 respectively). These affinity values are in line with literature affinities of ketanserin and Mesulergine at 5-HT2A receptors in various bioassays. The 5-CT-induced inhibition of PGF2α-induced contraction was competitively antagonized by Mesulergine (pKB estimate: 8.52±0.12) and by the selective 5-HT7 receptor antagonist SB-269970 (pKB estimate: 9.36±0.14). Both pKB estimates are in line with literature affinities of these compounds for 5-HT7 receptors. Mesulergine (30 nM) and SB-269970 (10 nM) shifted the relaxant curve to 5-HT parallel to the right in the presence of ketanserin (0.3 μM) (pA2 estimates of 8.08±0.10 and 8.75±0.14 respectively), indicative of 5-HT7 receptor involvement. It is concluded that 5-HT induces dog proximal stomach (LM) contraction via smooth muscle 5-HT2A receptors and relaxation via smooth muscle 5-HT7 receptors. British Journal of Pharmacology (2002) 136, 321–329; doi:10.1038/sj.bjp.0704716

Jan A J Schuurkes - One of the best experts on this subject based on the ideXlab platform.

  • evidence for 5 ht7 receptors mediating relaxation of human colonic circular smooth muscle
    British Journal of Pharmacology, 1999
    Co-Authors: Nh Prins, M R Briejer, Patrick Van Bergen, L M A Akkermans, Jan A J Schuurkes
    Abstract:

    5-HT4 receptors mediate relaxation of human colon circular muscle. However, after 5-HT4 receptor blockade (SB 204070 10 nM), 5-HT still induced a relaxation (pEC50 6.3). 5-HT4 receptors were sufficiently blocked, as the curves to 5-HT obtained in the presence of 10 and 100 nM SB 204070 were indistinguishable. This 5-HT-induced relaxation was tetrodotoxin-insensitive, indicative of a smooth muscle relaxant 5-HT receptor. This, and the rank order of potency (5-CT=5-MeOT=5-HT) suggested involvement of 5-HT1 or 5-HT7 receptors. Mesulergine, a 5-HT7 receptor antagonist at nanomolar concentrations, and a 5-HT1 receptor antagonist at micromolar concentrations, competitively antagonized the 5-HT-induced relaxation (pKB 8.3) and antagonized the relaxation to 5-CT. Methysergide antagonized the 5-HT-induced relaxation (pA2 7.6). It is concluded that the profile of the smooth muscle inhibitory 5-HT receptor resembles that of the 5-HT7 receptor. These data provide the first evidence for functional human 5-HT7 receptors.

  • 5 ht receptor types in the rat ileum longitudinal muscle focus on 5 ht2 receptors mediating contraction
    Neurogastroenterology and Motility, 1997
    Co-Authors: M R Briejer, C Mathis, Jan A J Schuurkes
    Abstract:

    The 5-hydroxytryptamine (5-HT) receptor(s) that mediate(s) contraction of the rat ileum longitudinal muscle was studied. 5-HT and α-methyl-5-HT equipotently induced contractions, whereas 5-methoxytryptamine and 2-methyl-5-HT (partial agonist) were less potent; this rank order of potency suggests involvement of a 5-HT2 receptor. Neither tetrodotoxin nor atropine affected the contraction to 5-HT, suggesting a smooth muscle localization of these 5-HT2 receptors. The presence of either a selective 5-HT2B (SB 204741), 5-HT3 (granisetron) or 5-HT4 (SB 204070) antagonist, slightly affected the contractions to 5-HT. Thus, they were also included in the organ bath solution in all subsequent experiments in order to pharmacologically isolate the main contractile component. Using (if possible) 5-HT2A receptor-selective concentrations, ketanserin, ritanserin, metergoline, spiperone, mianserin, methiothepin, Mesulergine, methysergide and cisapride all inhibited the contractions to 5-HT, causing a depression of the curve to 5-HT (i.e. surmountable antagonism was not observed with any of the above agents). Comparison of the affinities of these compounds for the various 5-HT2 receptor subtypes revealed that the receptor involved in the contractions to 5-HT most closely resembles the 5-HT2A receptor. However, cinanserin at a concentration expected to inhibit 5-HT2A receptor-mediated effects, failed to affect the contractions to 5-HT. It is thus concluded that on the longitudinal smooth muscle of the rat ileum, at least a part of the contraction to 5-HT is mediated by 5-HT receptors resembling the 5-HT2A receptor subtype.

Nh Prins - One of the best experts on this subject based on the ideXlab platform.

  • smooth muscle 5 ht2a receptors mediating contraction of porcine isolated proximal stomach strips
    British Journal of Pharmacology, 2002
    Co-Authors: Pieter Janssen, Nh Prins, Ann Meulemans, Romain Lefebvre
    Abstract:

    The aim of this study was to characterize the 5-HT receptors involved in the 5-HT-induced contraction of longitudinal muscle (LM) strips of porcine proximal stomach. This was done in a classical organ bath set-up for isotonic measurement. The concentration-contraction curve to 5-HT was not modified by 5-HT3 and 5-HT4 receptor antagonism. Methysergide, ketanserin and Mesulergine antagonized the curve to 5-HT. Concomitantly, increasing concentrations of ketanserin and Mesulergine progressively revealed a biphasic nature of the 5-HT curve. Ketanserin antagonized the low-affinity receptor while it did not modify the high-affinity receptor. Tetrodotoxin did not influence the concentration-contraction curve to 5-HT neither in the absence nor presence of ketanserin, indicating that nerves are not involved. Ketanserin competitively antagonized the monophasic concentration-response curve to α-Methyl-5-HT, yielding a Schild slope that was not significantly different from unity. After constraining the Schild slope to unity, a pKB estimate of 8.23±0.90 was obtained. This affinity estimate of ketanserin closely approximates previously reported affinities at 5-HT2A receptors. In the presence of ketanserin (0.1 μM; exposing the high-affinity receptor), a wide range of 5-HT receptor antagonists covering all 5-HT receptors known, was tested. Only methysergide and ritanserin inhibited the response to 5-HT, thus expressing affinity for the high-affinity receptor. This did not reveal the identity of the receptor involved. It can be concluded that 5-HT induces pig proximal stomach (LM) contraction via 5-HT2A receptors located on smooth muscle. A ketanserin-insensitive phase of contractions could not be characterized between the actually known classes of 5-HT receptors with the pharmacological tools that were used. British Journal of Pharmacology (2002) 137, 1217–1224. doi:10.1038/sj.bjp.0704992

  • pharmacological characterization of the 5 ht receptors mediating contraction and relaxation of canine isolated proximal stomach smooth muscle
    British Journal of Pharmacology, 2002
    Co-Authors: Pieter Janssen, Nh Prins, Al Meulemans, Romain Lefebvre
    Abstract:

    We aimed to characterize 5-HT receptors mediating contraction and relaxation to 5-HT in dog proximal stomach longitudinal muscle (LM) strips. Of the tryptamine analogues tested, 5-HT was the most potent contractile agent at basal length, while 5-CT was the most potent relaxant of PGF2α-induced contraction. Neither the contractions to 5-HT, nor the relaxations to 5-CT were influenced by tetrodotoxin, illustrating that action potential propagation is not involved. The 5-HT-induced contraction was antagonized by Mesulergine (0.03 to 0.3 μM) and ketanserin (2–20 nM), but the antagonism was not of a simple competitive nature, indicating multiple receptor involvement. Ketanserin (3 to 30 nM) and Mesulergine (30 nM) competitively antagonized the α-Me-5-HT-induced contraction (pKB: 8.83±0.09 and pA2: 8.25±0.06 respectively). These affinity values are in line with literature affinities of ketanserin and Mesulergine at 5-HT2A receptors in various bioassays. The 5-CT-induced inhibition of PGF2α-induced contraction was competitively antagonized by Mesulergine (pKB estimate: 8.52±0.12) and by the selective 5-HT7 receptor antagonist SB-269970 (pKB estimate: 9.36±0.14). Both pKB estimates are in line with literature affinities of these compounds for 5-HT7 receptors. Mesulergine (30 nM) and SB-269970 (10 nM) shifted the relaxant curve to 5-HT parallel to the right in the presence of ketanserin (0.3 μM) (pA2 estimates of 8.08±0.10 and 8.75±0.14 respectively), indicative of 5-HT7 receptor involvement. It is concluded that 5-HT induces dog proximal stomach (LM) contraction via smooth muscle 5-HT2A receptors and relaxation via smooth muscle 5-HT7 receptors. British Journal of Pharmacology (2002) 136, 321–329; doi:10.1038/sj.bjp.0704716

  • evidence for 5 ht7 receptors mediating relaxation of human colonic circular smooth muscle
    British Journal of Pharmacology, 1999
    Co-Authors: Nh Prins, M R Briejer, Patrick Van Bergen, L M A Akkermans, Jan A J Schuurkes
    Abstract:

    5-HT4 receptors mediate relaxation of human colon circular muscle. However, after 5-HT4 receptor blockade (SB 204070 10 nM), 5-HT still induced a relaxation (pEC50 6.3). 5-HT4 receptors were sufficiently blocked, as the curves to 5-HT obtained in the presence of 10 and 100 nM SB 204070 were indistinguishable. This 5-HT-induced relaxation was tetrodotoxin-insensitive, indicative of a smooth muscle relaxant 5-HT receptor. This, and the rank order of potency (5-CT=5-MeOT=5-HT) suggested involvement of 5-HT1 or 5-HT7 receptors. Mesulergine, a 5-HT7 receptor antagonist at nanomolar concentrations, and a 5-HT1 receptor antagonist at micromolar concentrations, competitively antagonized the 5-HT-induced relaxation (pKB 8.3) and antagonized the relaxation to 5-CT. Methysergide antagonized the 5-HT-induced relaxation (pA2 7.6). It is concluded that the profile of the smooth muscle inhibitory 5-HT receptor resembles that of the 5-HT7 receptor. These data provide the first evidence for functional human 5-HT7 receptors.