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A Surprenant

Publications and source records attributed to A Surprenant.

At least 55 records · Page 3Linked to original sources
PubMed1996

Functional properties of native and cloned P2X receptors.

Electrophysiological experiments on dissociated smooth muscle and neurons have revealed three distinct phenotypes of P2X receptor: (1) a rapidly desensitizing, beta-methylene ATP-sensitive response typical of most smooth muscle; (2) a non-desensitizing, alpha,beta-methylene ATP-insensitive response characteristic of PC12 phaeochromocytoma cells and rat superior cervical ganglion neurons; and (3) a non-desensitizing, alpha, beta-methylene ATP-sensitive response observed in sensory neurons. All of these purinoceptors share a similar cationic and high Ca2+ permeability and sensitivity to blockade by suramin, Cibacron blue, oxidized ATP, pyridoxal-5-phosphate and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid. Heterologous expression of two forms of cloned P2X receptors (from rat vas deferens and PC12 cells) reveals that each cloned receptor can reconstitute native responses with remarkable fidelity. Such results suggest that homo-oligomeric channels may be formed from single subunits of the P2X receptor in smooth muscle, PC12 cells and some neurons. The third phenotype observed in native cells might result from co-assembly of subunits of the cloned receptors. However, co-expression studies show that these two forms of the P2X receptor do not heteropolymerize. Therefore, the non-desensitizing, alpha, beta-methylene ATP-sensitive response observed in sensory neurons may result from a distinct P2X receptor or from heteropolymerization of more than one distinct P2X purinoceptor.

Adenosine Triphosphate↗
PubMed1996

A comparison of the binding characteristics of recombinant P2X1 and P2X2 purinoceptors.

1. We have recently provided evidence that [35S]-adenosine 5'-O-[3-thiotriphosphate] ([35S]-ATP gamma S) can label the human bladder recombinant P2X1 purinoceptor (human P2X1 purinoceptor). In this study we have characterized the binding of [35S]-ATP gamma S to a second P2X purinoceptor subtype, the rat PC12 phaeochromocytoma cell recombinant P2X2 purinoceptor (rat P2X2 purinoceptor), and compared its binding properties with those of both endogenous and recombinant P2X1 purinoceptors. 2. Infection of CHO-K1 cells with the rat P2X2 purinoceptor using Semliki forest virus (SFV) resulted in the expression of high affinity (pKd = 9.3; Bmax = 18.1 pmol mg-1 protein) binding sites for [35S]-ATP gamma S but not for [3H]-alpha, beta-methylene ATP ([3H]-alpha beta meATP). Since functional P2X purinoceptors could be detected electrophysiologically in these cells, but not in non-infected or CHO-K1 cells infected with SFV containing the LacZ gene, these results suggest that the rat P2X2 purinoceptor can be labelled using [35S]-ATP gamma S. 3. The binding characteristics of the rat P2X2 purinoceptor were compared with those of the human P2X1 purinoceptor, which was also expressed in the CHO-K1 cells using SFV. A major difference between the two recombinant P2X purinoceptor types was in the binding characteristics of alpha, beta-methylene ATP (alpha beta meATP). Thus, in the absence of divalent cations, alpha beta meATP possessed low affinity for both the human P2X1 purinoceptor (pIC50 = 7.2) and rat P2X2 purinoceptor (pIC50 = 7.1) labelled using [35S]-ATP gamma S. However, when the recombinant P2X purinoceptors were labelled with [3H]-alpha beta meATP in the presence of 4 mM CaCl2, the affinity of alpha beta meATP for the human P2X1 purinoceptor increased (pIC50 for alpha beta meATP = 8.2), while the affinity of the rat P2X2 purinoceptor for alpha beta meATP did not change (pIC50 for alpha beta meATP = 6.8). 4. Affinity estimates of 15 other nucleotide analogues for the [35S]-ATP gamma S binding sites on the two recombinant P2X purinoceptor subtypes were surprisingly similar (less than 5 fold difference), the only exception being 2'-deoxy ATP which possessed 8 fold higher affinity for rat P2X2 than for human P2X1 purinoceptors. In contrast dextran sulphate and the P2 purinoceptor antagonists, pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid and 4,4'-diisothiocyanatostilbene-2,2' disulphonic acid, possessed 7 to 33 fold higher affinity for the human P2X1 than for the rat P2X2 purinoceptor. These data provide a correlation coefficient (r) of 0.894. 5. There was some evidence for species differences in the P2X1 purinoceptor. Thus, most nucleotides possessed slightly greater (up to 9-10 fold), while the P2 purinoceptor antagonists possessed slightly lower (up to 7-16 fold), affinity for the endogenous rat vas deferens and rat bladder P2X1 purinoceptors than for the human recombinant P2X1 purinoceptor. These differences were reflected in a slightly lower correlation coefficient, when comparing across species between the human recombinant P2X1 purinoceptor and the endogenous P2X1 purinoceptors labelled in either the rat deferens (r = 0.915) or the rat bladder (r = 0.932), than when comparing within species between the endogenous rat vas deferens and rat bladder P2X1 purinoceptors (r = 0.995). 6. In summary, [35S]-ATP gamma S can be used to label the recombinant P2X1 and P2X2 purinoceptors. Despite the marked differences reported between these two forms of P2X purinoceptor in functional studies, the differences in binding studies were more limited. However, a number of antagonists could discriminate between the P2X purinoceptor subtypes in the binding studies raising expectations that selective antagonists for these receptors can be developed.

Adenosine Triphosphate↗
PubMed1996

The binding characteristics of a human bladder recombinant P2X purinoceptor, labelled with [3H]-alpha beta meATP, [35S]-ATP gamma S or [33P]-ATP.

1. The binding of [3H]-alpha beta meATP, [35s]-ATP gamma S and [alpha 33P]-ATP to a human bladder P2X purinoceptor, transiently expressed in CHO-K1 cells using the Semliki Forest Virus (SFV) expression system, was examined. The characteristics of the binding sites were compared with results obtained in rat vas deferens, a tissue in which the radioligands are thought to label P2X purinoceptors and in which the endogenous P2X purinoceptor displays high homology with the human bladder P2X purinoceptor. 2. In non-infected CHO-K1 cells, 100 microM ATP evoked only small inward currents (40 pA) in approximately 30% of the cells when studied by the whole-cell voltage clamp technique. In membranes prepared from either these non-infected cells or cells infected with SFV containing the LacZ gene (SFV-LacZ), [3H]-alpha beta meATP bound with low affinity (pKd = 7.04; Bmax = 8.88 pmol ml-1 protein) and there was only a low density of [35S]-ATP gamma S binding sites (pKd = 8.74; Bmax = 358 fmol ml-1 protein). These binding sites differed from those present in rat vas deferens. Thus, pIC50 values for alpha beta meATP (6.5) and L-beta gamma meATP (4.0) at the [3H]-alpha beta meATP binding sites in non-infected CHO-K1 cells were much lower than the respective pIC50 values of 8.3 and 7.7, determined in rat vas deferens. Similarly, affinity estimates (pIC50 values) for ATP (6.82), 2-meS-ATP (5.43), ATP gamma S (7.06) and alpha beta meATP (4.84) at the [35S]-ATP gamma S binding sites in non-infected CHO-K1 cells were up to 2291 fold lower than the respective values of 9.01, 8.79, 8.73 and 7.57, determined in rat vas deferens. 3. In CHO-K1 cells infected using SFV containing the cDNA for the human bladder P2X purinoceptor (SFV-h.P2X), ATP, 2-meS-ATP and alpha beta meATP evoked large inward currents (2-7 nA) in whole cell voltage clamp studies. In membranes prepared from these SFV-h.P2X infected cells, [3H]-alpha beta meATP binding was increased, compared to that measured in the non infected or SFV-LacZ infected cells, with only high affinity [3H]-alpha beta meATP binding sites being detected (pKd = 9.21; Bmax = 3.54 pmol mg-1 protein). The pIC50 values for alpha beta meATP (8.2) and L-beta gamma meATP (7.2) in competing for these sites were the same or similar to the values determined in rat vas deferens. 4. A high density of [35H]-ATP gamma S binding sites (pKd = 9.09; Bmax = 6.82 pmol mg-1 protein) was also present in the membranes from CHO-K1 cells infected with SFV-h.P2X and affinity estimates (pIC50 values) for ATP (8.93), 2-meS-ATP (8.23), ATP gamma S (8.08), and alpha beta meATP (7.17) at competing for these sites were as much as 631 fold higher than the respective values determined in non-infected CHO-K1 cells but were close to the values determined in rat vas deferens. Similar data were obtained with [alpha 33P]-ATP as radioligand. 5. These data suggest that [3H]-alpha beta meATP, [35S]-ATP gamma S and [33P]-ATP label the human bladder recombinant P2X purinoceptor expressed in CHO-K1 cells following infection with SFV-h.P2X and provide further corroborative evidence to support the contention that the high affinity binding sites for these radioligands in rat vas deferens are P2X purinoceptors.

Adenosine Triphosphate↗
PubMed1996

Neural reflexes controlling intestinal microcirculation.

It has long been established that neural reflexes are involved in the regulation of gastrointestinal vascular function, in particular the mucosal hyperemia that follows food ingestion. However, more precise identification of reflex pathways involved in the control of mucosal blood flow had not previously been forthcoming because of a lack of adequate methods to examine resistance arterioles within the intestinal wall. Recent advances have employed novel in vitro preparations and videomicroscopic techniques to investigate the neural control of the gastrointestinal microvasculature and involvement of intrinsic and extrinsic vasodilatory neurons in mucosal reflexes. Vasoconstrictor innervation to submucosal arterioles is mediated solely by extrinsic sympathetic nerves that release ATP onto arteriolar P2n-purinoceptors. Neurogenic vasodilation of submucosal arterioles occurs by release of acetylcholine and/or neuropeptides from intrinsic submucosal neurons as well as by release of substance P and calcitonin gene-related peptide from extrinsic sensory nerves. Both vasodilator pathways can be activated independently by mucosal stimulation, and both have afferent and efferent components confined to the mucosa and submucosal neuronal plexus. We speculate that the intrinsic enteric cholinergic reflex pathways are involved in local physiological control of mucosal blood flow, whereas extrinsic sensory reflex pathways are preferentially activated during inflammatory states.

Animals↗
PubMed1995

Coexpression of P2X2 and P2X3 receptor subunits can account for ATP-gated currents in sensory neurons.

Cation-selective P2X receptor channels were first described in sensory neurons where they are important for primary afferent neurotransmission and nociception. Here we report the cloning of a complementary DNA (P2X3) from rat dorsal root ganglia that had properties dissimilar to those of sensory neurons. We also found RNA for (P2X1)(ref. 7), (P2X2)(ref. 8) and P2X4 (ref. 9) in sensory neurons; channels expressed from individual cDNAs did not reproduce those of sensory ganglia. Coexpression of P2X3 with P2X2, but not other combinations, yielded ATP-activated currents that closely resembled those in sensory neurons. These properties could not be accounted for by addition of the two sets of channels, indicating that a new channel had formed by subunit heteropolymerization. Although in some tissues responses to ATP can be accounted for by homomeric channels, our results indicate that ATP-gated channels of sensory neurons may form by a specific heteropolymerization of P2X receptor subunits.

Adenosine Triphosphate↗
PubMed1995

Electrophysiological properties of P2X-purinoceptors in rat superior cervical, nodose and guinea-pig coeliac neurones.

1. Whole-cell recordings were made from guinea-pig coeliac, rat nodose and rat superior cervical (SCG) neurones in culture, and currents in response to fast-flow (concentration clamp) application of ATP and other ATP analogues were measured. 2. At a holding potential of -70 mV, ATP evoked inward currents in all neurons. ATP-induced currents reversed at approximately 0 mV and showed strong inward rectification. Halving the external sodium concentration shifted the reversal potential by -15 to -17 mV, while increasing external potassium from 2 to 20 mM produced a 6-10 mV shift in reversal potential. Latency to onset of ATP current was < 1 ms; rise time was concentration dependent with maximum time to peak of 5-20 ms in nodose and coeliac neurones but 80 ms in superior cervical neurones. 3. Threshold concentrations of ATP were 0.1 microM for nodose and coeliac neurones but 10 microM for superior cervical neurones; EC50 values were approximately 3 microM for both nodose and coeliac neurones and 43 microM for superior cervical ganglia. Hill slopes for ATP concentration-response curves were not significantly different from unity in nodose and coeliac neurones whereas the Hill slope in superior cervical neurones was two. 4. 2-MethylthioATP (2-MeSATP) acted as a full agonist in all three neuronal preparations; EC50 values were 0.4, 2.8 and 46 microM for nodose, coeliac and superior cervical neurones, respectively. alpha,beta-Methylene ATP (alpha,beta-MeATP) was a full agonist in nodose and coeliac neurones with EC50 values of 9 and 13 microM, respectively. 5. In superior cervical neurones alpha,beta-MeATP had little or no agonist action but produced a concentration-dependent attenuation of the ATP current. Thus, alpha, beta-MeATP appears to behave as a partial agonist at P2X-purinoceptors in superior cervical neurones. 6. The non-selective purinoceptor antagonists suramin (1-100 microM) and pyridoxal-5'-phosphate (30 microM), as well as the putative P2Y-selective antagonist, Cibacron Blue (30 microM), inhibited all agonist-evoked responses to a similar degree in all three neuronal populations. 7. This study demonstrates that an agonist potency profile of 2-MeSATP > or = ATP > or = alpha,beta-MeATP is characteristic of ligand-gated P2X-purinoceptors in isolated peripheral neurones. We also suggest that the P2X-receptor in superior cervical neurones may represent a distinct subtype of P2X-purinoceptor from that present in nodose and coeliac neurones.

Adenosine Triphosphate↗
PubMed1995

The selective P2X purinoceptor agonist, beta,gamma-methylene-L-adenosine 5'-triphosphate, discriminates between smooth muscle and neuronal P2X purinoceptors.

The effects of the putative selective P2X purinoceptor agonist, beta,gamma-methylene-L-adenosine 5'-triphosphate (beta gamma me-L-ATP), were determined at rat neuronal and smooth muscle P2X purinoceptors. beta gamma Me-L-ATP had no effect on the extracellularly recorded membrane potential of the rat isolated vagus nerve preparation at concentrations up to 300 microM. In contrast, the archetypal P2X purinoceptor agonist, alpha,beta-methylene ATP (alpha beta meATP; 1-100 microM), produced concentration-related depolarisation responses with a mean EC50 value of 10.8 microM. The depolarising effects of alpha beta meATP were not attenuated by beta gamma me-L-ATP (100 microM). In voltage clamp experiments on single nodose ganglion neurones, ATP (100 microM), but not beta gamma me-L-ATP (1-300 microM), evoked rapid (< 20 ms onset) inward currents when applied using a concentration-clamp method. In receptor binding studies to rat brain membranes, beta gamma me-D-ATP and alpha beta meATP competed with high affinity for [3H]alpha beta meATP binding sites, with mean pIC50 values of 7.7 and 8.3, respectively. However, beta gamma me-L-ATP possessed low affinity for these sites and competed only at concentrations in excess of 10 microM (mean pIC50 value 4.1). In prostatic segments of the rat vas deferens, beta gamma me-L-ATP (1-100 microM) and alpha beta meATP (0.3-100 microM) each produced concentration-related contractile responses with mean EC50 values of 17.1 and 3.6 microM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1995

New insights on P2X purinoceptors.

Significant advances in understanding of P2X purinoceptor pharmacology have been made in the last few years. The limitations of nucleotide agonists as drug tools have now been amply demonstrated. Fortunately, inhibitors of the degrading ecto-ATPase enzymes are becoming available and it has become apparent that the complete removal of all divalent cations can be used experimentally in some systems to prevent nucleotide breakdown. Despite these issues, convincing evidence for P2X receptor heterogeneity, from data with agonists, has recently been reported. A number of new antagonists at P2X purinoceptors have also recently been described which to some degree appear to be more specific and useful than earlier antagonists like suramin. It is now apparent that suramin is a poor antagonist of ATP in many tissues because it potently inhibits ATPase activity at similar concentrations to those at which it blocks the P2X purinoceptor. Advances in the use of radiolabelled nucleotides as radioligands for binding studies has allowed the demonstration of P2X purinoceptors in a variety of tissues throughout the body including the brain. These studies have also provided evidence for receptor heterogeneity. Excitingly, two P2X purinoceptor genes have been cloned but operational studies suggest that more than two types exist. The cloning studies have also demonstrated a unique structure for the P2X purinoceptor which differentiates it from all other ligand-gated ion channel receptors. Further studies on P2X purinoceptor operation and structure are needed to help resolve controversies alluded to regarding the characterization and classification of nucleotide receptors. Hopefully such studies will also lead to a better understanding of the physiological and pathological importance of ATP and its activation of P2X purinoceptors. This will require the identification of better drug tools, in particular antagonists which may also provide the basis for novel therapeutic agents.

Adenosine Triphosphate↗
PubMed1995

P2X receptors bring new structure to ligand-gated ion channels.

P2X receptors are cation-selective ion channels that open on binding to extracellular ATP; they play a role in fast synaptic transmission between neurones, and from autonomic nerves to smooth muscles. Isolation of cDNAs that encode P2X receptors in the smooth muscle of vas deferens and in phaeochromocytoma cells indicates that the receptors are not related to other ligand-gated ion channels. Their overall structure resembles more closely that of epithelial Na+ channels and the proteins that are thought to form mechanosensitive channels in Caenorhabditis elegans. The type of P2X RNA that is found in vas deferens is expressed preferentially by apoptotic thymocytes, and the type of P2X RNA that is found in PC12 cells is abundant in the pituitary gland, suggesting hitherto unsuspected roles for ATP-gated channels in endocrine and immune function.

Adenosine Triphosphate↗
PubMed1995

A study on P2X purinoceptors mediating the electrophysiological and contractile effects of purine nucleotides in rat vas deferens.

1. We have studied both the electrophysiological and contractile effects of the purine nucleotide, adenosine-5'-triphosphate (ATP), as well as a number of its structural analogues as agonists at P2X purinoceptors in the rat vas deferens in vitro. 2. Electrophysiological effects were investigated by a whole cell voltage clamp technique (holding potential-70 mV) with fast flow concentration-clamp applications of agonists in single isolated smooth muscle cells. ATP, 2-methylthio adenosine-5'-triphosphate (2-MeSATP) and alpha,beta methylene adenosine-5'-triphosphate (alpha,beta-meATP) all evoked inward currents over a similar concentration range (0.3-10 microM), being approximately equipotent with similar concentrations for threshold effects (0.3 microM). ADP (10 microM) also evoked a rapid current of similar peak amplitude to that seen with ATP (10 microM). 3. alpha,beta-meATP was the most potent agonist in producing concentrations of the rat vas deferens whole tissue preparation, with a threshold concentration equal to that in the electrophysiological studies (0.3 microM). However, ATP and 2-MeSATP were at least ten times less potent in studies measuring contraction than in the electrophysiological studies. Furthermore, their concentration-effect curves were shallow with smaller maximal responses than could be achieved with alpha,beta-meATP. ADP, AMP and adenosine were inactive at concentrations up to 1 mM. The rank order of agonist potencies observed for contraction was alpha,beta-meATP >> ATP = 2-MeSATP. 4. Measurement of inorganic phosphate (iP), as a marker of purine nucleotide metabolism in the vasdeferens whole tissue preparation, indicated that ATP and 2-MeSATP were rapidly metabolized,whereas alpha,beta-meATP was stable for up to 2 h. Removal of divalent cations prevented breakdown of ATP and 2-MeSATP, suggesting that metabolism involved a Ca2+/Mg2+-dependent enzyme.5. It appears that in isolated preparations of rat vas deferens, the low potency of ATP and 2-MeSATP can be explained by rapid agonist breakdown by ectonucleotidases. However, this is not the case in the single cell studies where the use of rapid concentration-clamp applications revealed the true potency of the agonists. Under such conditions the three agonists were all equal in potency indicating that the rank order of agonist potencies of alpha,beta-meATP>> ATP = 2-MeSATP is not in fact characteristic of smooth muscle P2x-purinoceptors as commonly believed.

Adenosine Triphosphate↗
PubMed1995

Pharmacological characterization of heterologously expressed ATP-gated cation channels (P2x purinoceptors).

cDNAs encoding P2x purinoceptors from human bladder smooth muscle and from rat PC-12 cells were expressed in oocytes and human embryonic kidney 293 cells. Agonist potencies of 2-methylthio-ATP = 2-chloro-ATP = ATP > = 2'- and 3'-O-(4-benzoylbenzoyl)-ATP > or = adenosine-5'-O-(3-thio)-triphosphate > or = P1,P5-di(adenosine-5') pentaphosphate >> ADP prevailed for both P2x purinoceptors. There were two main differences in agonist sensitivity between the two receptors. First, ATP was 10 times more potent at the receptor from bladder (EC50, 0.8 microM) than at the receptor from PC-12 cells (EC50, 8.2 microM). Second, alpha,beta-methylene-ATP and L- and D-beta,gamma-methylene-ATP were agonists in cells expressing the bladder smooth muscle receptor (EC50, 1-3 microM) but were ineffective in cells expressing the PC-12 receptor. The P2 purinoceptor antagonists suramin, pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid, and pyridoxal-5-phosphate acted similarly at both receptor forms, producing noncompetitive inhibition, with IC50 values of 1-5 microM for suramin and pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid and 10-20 microM for pyridoxal-5-phosphate. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid distinguished receptor subtypes, producing potent inhibition of the bladder smooth muscle P2x-mediated response, with an IC50 value of 3 microM; it inhibited the PC-12 form by < 40% at 100 or 300 microM. This study thus defines the pharmacological properties of homo-oligomeric forms of these two types of cloned P2x receptor channels.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

A new class of ligand-gated ion channel defined by P2x receptor for extracellular ATP.

Extracellular ATP exerts its effects through P2 purinoceptors: these are ligand-gated ion channels (P2x) or G-protein-coupled receptors (P2Y, P2U). ATP at P2x receptors mediates synaptic transmission between neurons and from neurons to smooth muscle, being responsible, for example, for sympathetic vasoconstriction in small arteries and arterioles. We have now cloned a complementary DNA encoding the P2x receptor from rat vas deferens and expressed it in Xenopus oocytes and mammalian cells. ATP activates a cation-selective ion channel with relatively high calcium permeability. Structural predictions suggest that the protein (399 amino acids long) is mostly extracellular and contains only two transmembrane domains plus a pore-forming motif which resembles that of potassium channels. The P2x receptor thus defines a new family of ligand-gated ion channels.

Adenosine Triphosphate↗
PubMed1994

Single channel properties of the 5-HT3 subtype of serotonin receptor in primary cultures of rodent hippocampus.

Whole cell and outside-out patch clamp recordings were obtained from primary cultures of rat and mouse hippocampal neurons. Serotonin (5-HT) evoked short-latency fast inward currents in about 5% of neurons. These currents reversed near 0 mV, showed inward rectification, and were inhibited by the 5-HT3 receptor antagonists ICS 205-930, ondansetron and tubocurare. 5-HT activated single channel currents in 14 of 24 membrane patches obtained from neurons which showed 5-HT3-activated whole cell currents; mean amplitude of channel openings was 0.95 +/- 0.09 pA at -100 mV. Chord conductances measured at -80 and -160 mV were 8.3 and 10.5 pS, respectively. 5-HT-induced unitary currents were blocked reversibly by tubocurare (1 microM), ICS 205-930 (30 nM) and ondansetron (100 nM). Thus, single-channel properties of 5-HT3 receptors in hippocampal neurons are similar to those present in peripheral neurons and do not exhibit solely the sub-picosiemen conductance characteristic of the neuroblastoma and neuroblastoma-derived cloned 5-HT3 receptor.

Animals↗
PubMed1994

Morphological properties and projections of electrophysiologically characterized neurons in the guinea-pig submucosal plexus.

Intracellular recordings were made from 73 guinea-pig submucosal neurons using neurobiotin-filled microelectrodes; subsequently, neuropeptide immunoreactivity, morphology and nerve fibre projections were determined. Five distinct groups of cells could be distinguished: S cells with inhibitory input (61%), S cells without inhibitory input (19%), AH cells (8%), S-AH cells (5%), and glial networks. S cells with inhibitory input were immunoreactive for vasoactive intestinal polypeptide and showed Dogiel Type III morphology with the axon branching and coursing through two to 12 ganglia; varicosities and tufts of varicosities were observed surrounding other cell bodies as well as over blood vessels. S cells without inhibitory input primarily were immunoreactive for neuropeptide Y; they also showed Dogiel Type III morphology and similar, though shorter, axonal projections and varicose features surrounding other neurons. AH cells, which most likely contained substance P, lacked synaptic input and exhibited Dogiel Type II morphology; they branched more extensively than S cells and also formed varicose tufts within other ganglia. S-AH cells combined electrophysiological properties of S cells with inhibitory input and AH cells and did not show consistent morphological or histochemical characteristics. Typical glial networks were observed; in addition, on two occasions unusual networks of dye and electrical coupling between S cells without inhibitory input and a glial complex were observed. These results suggest that vasoactive intestinal polypeptide-containing S cells may act as interneurons which mediate a slow excitatory synaptic potential; that neuropeptide Y-containing S cells, which are known to be cholinergic, may play a role as cholinergic interneurons mediating the nicotinic fast excitatory synaptic potential; and that AH neurons also may provide cholinergic innervation to other submucosal neurons in addition to their previously described dual projections into mucosa and myenteric plexus.

Action Potentials↗
PubMed1993

ATP in synapses.

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Adenosine Triphosphate↗
PubMed1993

Effects of phospholipase A2 inhibitors on coupling of alpha 2-adrenoceptors to inwardly rectifying potassium currents in guinea-pig submucosal neurones.

1. Noradrenaline hyperpolarizes guinea-pig submucosal neurones by opening inwardly rectifying potassium channels. Intracellular recordings were made from submucosal neurones and the possible involvement of the phospholipase A2 pathway in this response was examined. 2. The non-specific phospholipase A2 inhibitors, quinacrine (10 microM) and 4-bromophenacyl bromide (4-BPB, 10 microM) inhibited nerve-evoked inhibitory synaptic potentials (i.p.s.ps) and hyperpolarizations to somatostatin and UK 14304. Quinacrine and 4-BPB also blocked the inward rectification present in current-voltage curves in the absence of somatostatin or UK 14304. 3. The more selective phospholipase A2 inhibitor, cyclosporin A (10 microM) and the lipoxygenase and cyclo-oxygenase inhibitor, eicosatetraynoic acid (ETYA, 20 microM) and nordihydroguairetic acid (NDGA, 20 microM) did not alter i.p.s.ps or hyperpolarizations to UK 14304. 4. Exogenously applied arachidonic acid (1-300 microM) did not mimic the i.p.s.p. or the hyperpolarization to UK 14304. 5. We conclude that arachidonic acid or its eicosanoid metabolites produced by phospholipase A2 stimulation are unlikely to be involved in the receptor G-protein coupled activation of potassium currents in submucosal neurones. The inhibition of the noradrenaline-induced hyperpolarization by quinacrine and 4-BPB is most likely due primarily to blockade of the basal inwardly rectifying potassium conductance present in these neurones.

Acetylcholine↗
PubMed1993

Common ionic mechanisms of excitation by substance P and other transmitters in guinea-pig submucosal neurones.

1. Intracellular recordings were made from submucosal neurones and single-electrode voltage-clamp methods were used to record membrane currents. The actions of substance P (SP), 5-hydroxytryptamine (5-HT), muscarine, vasoactive intestinal polypeptide (VIP), forskolin and nerve stimulation were studied. 2. Substance P, 5-HT (in the presence of 5-HT3 receptor antagonists), muscarine, VIP, forskolin and slow excitatory synaptic transmission all produced identical responses: an inward current associated with a membrane conductance decrease at the resting potential. The actions of any one occluded the actions of any other and all responses were pertussis-toxin insensitive. 3. These agonists produced a voltage-independent decrease in a 'leak' potassium conductance between -40 and -120 mV in 14% of neurones. 4. These agonists decreased a voltage-dependent, calcium-activated potassium conductance between -40 and -80 mV in all other (86%) neurones. The agonists still evoked an inward current without apparent conductance change at potentials between -90 and -130 mV. 5. In a low calcium solution containing cobalt or cadmium, the agonists produced an inward current associated with a conductance increase from -40 to -120 mV. Ion replacement studies indicated this current was due to an increase in a cation-selective (mainly sodium) conductance. 6. The agonists also reduced the inwardly rectifying potassium current that is activated by somatostatin and alpha 2-adrenoceptor agonists in these neurones. The agonists did not alter the inwardly rectifying potassium current that is present in these neurones in the absence of somatostatin or alpha 2-agonists. 7. Thus, SP, 5-HT, muscarine, VIP and the release of slow excitatory transmitters all appear to act through a common intracellular transduction pathway, an increase in adenylate cyclase. This results in an activation of a sodium-selective cation current and an inhibition of three distinct potassium conductances: the background potassium conductance, the calcium-activated potassium conductance and the inwardly rectifying potassium conductance activated by somatostatin and alpha 2-adrenoceptor agonists.

Animals↗