Biomedical subjects

Susanna Fürst

Publications and source records attributed to Susanna Fürst.

8 recordsLinked to original sources

PubMed2005

Capsaicin-sensitive sensory neurons regulate myocardial function and gene expression pattern of rat hearts: a DNA microarray study.

We have previously shown that capsaicin-sensitive sensory nerves contribute to the regulation of normal cardiac function and to the development of cardiac adaptation to ischemic stress; however, the underlying molecular mechanisms remain unknown. Therefore, here we assessed cardiac functional alterations and relative gene expression changes by DNA microarray analysis of 6400 genes in rat hearts 7 days after the end of systemic capsaicin treatment protocol leading to selective sensory chemodenervation. Capsaicin pretreatment resulted in a cardiac dysfunction characterized by elevation of left ventricular end-diastolic pressure and led to altered expression of 80 genes of known function or homology to known sequences. Forty-seven genes exhibited significant up-regulation and 33 genes were down-regulated (changes ranged from -3.9 to +4.8-fold). The expression changes of 10 selected genes were verified, and an additional 11 genes were examined by real-time quantitative PCR. This is the first demonstration that gene expression changes in the heart due to capsaicin pretreatment included vanilloid receptor-1 (capsaicin receptor), transient receptor potential protein, GABA receptor rho-3 subunit, 5-hydroxytryptamine 3 receptor B, neurokinin receptor 2, endothelial nitric oxide synthase, matrix metalloproteinase-13, cytochrome P450, farnesyl-transferase, ApoB, and leptin. None of the genes have been previously shown to be involved in the mechanism of the cardiac functional effects of sensory chemodenervation by capsaicin. We conclude that capsaicin-sensitive sensory nerves play a significant role in the regulation of a variety of neuronal and non-neuronal genes in the heart and possibly in other tissues as well.

Animals↗

PubMed2005

Decrease of current responses at human recombinant P2X3 receptors after substitution by Asp of Ser/Thr residues in protein kinase C phosphorylation sites of their ecto-domains.

The whole-cell patch-clamp technique was used to record current responses to nucleotides in HEK 293 cells transiently transfected with the human (h) P2X(3) receptor. When GDP-beta-S was included into the pipette solution, UTP at concentrations which did not alter the holding current, facilitated the alpha,beta-methylene ATP (alpha,beta-meATP)-induced current. The substitution of Ser/Thr residues situated within protein kinase C (PKC) consensus phosphorylation sites of the P2X(3) receptor ecto-domain by the neutral amino acid Ala either abolished (T134A, S178A) or did not alter (T196A, S269A) the UTP-induced potentiation of the alpha,beta-meATP current. The substitution of the same Ser/Thr residues in all four PKC sites by the negatively charged Asp prevented the potentiation by UTP. The Asp mutations abolished the first, fast offset time-constant, but did not alter, or in the case of S269D even increased, the second, slow offset time-constant; at the same time such mutations invariably increased the onset time-constant and massively depressed the peak current amplitude. None of the Ala mutations (with the exception of S269A) influenced the time-course of desensitisation or the peak current amplitude. It is concluded that constitutive activation of PKC sites at the ecto-domain of the hP2X(3) receptor both abolishes the UTP-induced potentiation of the alpha,beta-meATP current and accelerates its rate of desensitisation.

Adenosine Triphosphate↗

PubMed2005

Regulation of human recombinant P2X3 receptors by ecto-protein kinase C.

The whole-cell patch-clamp technique was used to record current responses to nucleotides and nucleosides in human embryonic kidney HEK293 cells transfected with the human purinergic P2X3 receptor. When guanosine 5'-O-(3-thiodiphosphate) was included into the pipette solution, UTP at concentrations that did not alter the holding current facilitated the alpha,beta-methylene ATP (alpha,beta-meATP)-induced current. ATP and GTP, but not UDP or uridine, had an effect similar to that of UTP. Compounds known to activate protein kinase C (PKC) acted like the nucleoside triphosphates investigated, whereas various PKC inhibitors invariably reduced the effects of both PKC activators and UTP. The substitution by Ala of Ser/Thr residues situated within PKC consensus sites of the P2X3 receptor ectodomain either abolished (PKC2 and PKC3; T134A, S178A) or did not alter (PKC4 and PKC6; T196A, S269A) the UTP-induced potentiation of the alpha,beta-meATP current. Both the blockade of ecto-protein kinase C activity and the substitution of Thr-134 or Ser-178 by Ala depressed the maximum of the concentration-response curve for alpha,beta-meATP without altering the EC50 values. Molecular simulation of the P2X3 receptor structure indicated no overlap between assumed nucleotide binding domains and the relevant phosphorylation sites PKC2 and PKC3. alpha,beta-meATP-induced currents through native homomeric P2X3 receptors of rat dorsal root ganglia were also facilitated by UTP. In conclusion, it is suggested that low concentrations of endogenous nucleotides in the extracellular space may prime the sensitivity of P2X3 receptors toward the effect of subsequently applied (released) higher agonistic concentrations. The priming effect of nucleotides might be attributable to a phosphorylation of PKC sites at the ectodomain of P2X3 receptors.

Animals↗

PubMed2004

Peripheral versus central antinociceptive actions of 6-amino acid-substituted derivatives of 14-O-methyloxymorphone in acute and inflammatory pain in the rat.

Opioid analgesics with restricted access to the central nervous system represent a new approach to the treatment of severe pain with an improved safety profile. The objective of this study was to investigate the peripheral and central components of the antinociceptive actions of the 6-amino acid conjugates (glycine, alanine, and phenylalanine) of 14-O-methyloxymorphone. Their antinociceptive activities were compared with those of the centrally penetrating mu-opioid agonists morphine, fentanyl, and 14-O-methyloxymorphone. In the tail-flick test in rats, the 6-amino acid conjugates were 45- to 1170-fold more potent than morphine after i.c.v. administration and 19- to 209-fold after s.c. administration. They showed potencies similar to fentanyl after s.c. administration and were more potent after i.c.v. application. The time course of action was different between s.c. and i.c.v. administration, with significant long-lasting effects after i.c.v. administration. Systemic administration of the peripherally selective opioid antagonist naloxone methiodide antagonized the effects after s.c. but not after i.c.v. administration in the tail-flick test. Subcutaneous 6-amino acid derivatives also elicited antihyper-analgesic effects in the formalin test in rats, which were reversed by systemically administered naloxone methiodide. Although morphine exerts its analgesic effects by central and peripheral mechanisms, the investigated new opioids interact primarily with peripheral opioid receptors after s.c. administration. The present data indicate that the 6-amino acid conjugates of 14-O-methyloxymorphone have limited access to the central nervous system and can mediate antinociception at peripheral sites. Also, they might find clinical application when the central actions of opioids are unwanted.

Acute Disease↗

PubMed2004

Inhibition of N-type voltage-activated calcium channels in rat dorsal root ganglion neurons by P2Y receptors is a possible mechanism of ADP-induced analgesia.

Patch-clamp recordings from small-diameter rat dorsal root ganglion (DRG) neurons maintained in culture demonstrated preferential inhibition by ATP of high-voltage-activated, but not low-voltage-activated, Ca2+ currents (I(Ca)). The rank order of agonist potency was UTP > ADP > ATP. ATP depressed the omega-conotoxin GVIA-sensitive N-type current only. Pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) and 2'-deoxy-N6-methyladenosine 3',5'-bisphosphate tetraammonium, two P2Y1 receptor antagonists, almost abolished the ATP-induced inhibition. Both patch-clamp recordings and immunocytochemistry coupled with confocal laser microscopy indicated a colocalization of functional P2X3 and P2Y1 receptors on the same DRG neurons. Because the effect of ATP was inhibited by intracellular guanosine 5'-O-(2-thiodiphosphate) or by applying a strongly depolarizing prepulse, P2Y1 receptors appear to block I(Ca) by a pathway involving the betagamma subunit of a G(q/11) protein. Less efficient buffering of the intracellular Ca2+ concentration ([Ca2+]i) by reducing the intrapipette EGTA failed to interfere with the ATP effect. Fura-2 microfluorimetry suggested that ATP raised [Ca2+]i by a Galpha-mediated release from intracellular pools and simultaneously depressed the high external potassium concentration-induced increase of [Ca2+]i by inhibiting I(Ca) via Gbetagamma. Adenosine 5'-O-(2-thiodiphosphate) inhibited dorsal root-evoked polysynaptic population EPSPs in the hemisected rat spinal cord and prolonged the nociceptive threshold on intrathecal application in the tail-flick assay. These effects were not antagonized by PPADS. Hence, P2Y receptor activation by ADP, which is generated by enzymatic degradation of ATP, may decrease the release of glutamate from DRG terminals in the spinal cord and thereby partly counterbalance the algogenic effect of ATP.

Adenosine Diphosphate↗

PubMed2004

In vitro opioid activity profiles of 6-amino acid substituted derivatives of 14-O-methyloxymorphone.

A series of 6-amino acid conjugates (glycine, alanine and phenylalanine) of the highly potent opioid analgesic 14-O-methyloxymorphone was developed in an effort to obtain agonists that would have potentially limited ability to cross the blood-brain barrier. Binding studies revealed that all derivatives displayed high affinities (0.77-2.58 nM) at the mu-opioid receptor in rat brain membranes. They were potent agonists in mouse vas deferens preparation (IC(50)=5.52-26.8 nM). While the alpha-amino acid epimers are favoured by mu-opioid receptors, the beta-epimers proved to have increased interaction with delta-sites. Only the beta-phenylalanine conjugate showed some preference for delta- over mu-opioid receptors and delta-opioid receptor agonist activity. The relatively high delta-opioid receptor affinity of this analogue was also predicted by molecular modelling studies. The newly developed ionizable derivatives could find clinical applications as potent analgesics without the adverse actions of centrally acting opioids.

Analgesics, Opioid↗

PubMed2002

Involvement of central K(ATP) channels in the gastric antisecretory action of alpha2-adrenoceptor agonists and beta-endorphin in rats.

The intracerebroventricularly (i.c.v.) injected presynaptic alpha2-adrenoceptor agonists, clonidine and oxymetazoline, exerted a dose-dependent inhibition on the gastric acid secretion in pylorus-ligated rats; the ED50 values were 20 and 7.5 nmol/rat, respectively. Moreover, beta-endorphin, given i.c.v., also decreased acid secretion (ED50=0.25 nmol/rat i.c.v.). The antisecretory effect of these compounds was highly reduced by glibenclamide (10 nmol/rat i.c.v.), a selective blocker of K(ATP) channels. These results suggest that K(ATP) channels in the central nervous system are likely to be involved in the centrally initiated antisecretory action of both alpha2-adrenoceptor agonists and beta-endorphin.

Adrenergic alpha-2 Receptor Agonists↗

PubMed2002

Interaction between P2Y and NMDA receptors in layer V pyramidal neurons of the rat prefrontal cortex.

In the first part of this study, monosynaptic excitatory postsynaptic potentials (EPSPs) in layer V of the rat prefrontal cortex were evoked by electrical stimulation of layer I. Recordings by intracellular sharp microelectrodes showed that EPSPs were concentration-dependently facilitated by the P2 receptor antagonistic ATP analogue 2-methylthio ATP (2-MeSATP), while ATP itself depressed the synaptic potentials. The inhibitory effect of ATP turned into facilitation in the presence of the adenosine A(1) receptor antagonist DPCPX. The 2-MeSATP-induced potentiation of EPSP amplitudes were prevented by the P2 receptor antagonists PPADS and Suramin. The EPSP was almost abolished by coapplication of the NMDA receptor antagonist AP-5 and the AMPA/kainate receptor antagonist CNQX. After blockade of the NMDA receptor-mediated part of the EPSP by AP-5, the stimulatory effect of 2-MeSATP disappeared. When NMDA or AMPA were pressure-applied onto pyramidal cells, only the NMDA-induced depolarization was potentiated by 2-MeSATP. In the second part of the study, NMDA-induced currents were measured by whole-cell patch-clamp pipettes. ATP, 2-MeSATP, UDP and UTP potentiated the response to NMDA, while ADP-beta-S was inactive. PPADS antagonized the effect of ATP. Synaptic isolation of pyramidal neurons by a Ca(2+)-free medium or tetrodotoxin did not alter the effect of ATP which, however, was markedly depressed when GTP in the micropipette was replaced by GDP-beta-S. These observations suggest that in layer V pyramidal neurons of the prefrontal cortex postsynaptically localized P2Y receptors interact with NMDA receptor-channels.

Adenosine Triphosphate↗