Cat Lower Esophageal Sphincter Research Articles

Lysophosphatidic acid presynaptically blocks NO uptake during electric field stimulation-induced relaxation via LPA1 receptor in cat lower esophageal sphincter

Lysophosphatidic acid (LPA) is a lipid mediator that is involved in many biological responses, such as, in the stimulation/inhibition of proliferation, in cell migration, antiapoptosis, tumor cell invasion, platelet aggregation, vascular remodeling, and neurotransmitter release. In addition, LPA indirectly enhances the contractility of smooth muscle. Furthermore, electric field stimulation (EFS) causes contractions of isolated cat esophageal smooth muscle and relaxations of isolated cat lower esophageal sphincter (LES). To test whether or not LPA enhances postsynaptically-mediated contraction in cat esophageal smooth muscle and LES, both types of muscle strips were stimulated with muscarinic agonists. However, no significant effects were observed, and therefore, to investigate whether LPA is involved in presynaptic signal transduction, cat esophageal smooth muscle and LES were pretreated with LPA and stimulated using EFS. LPA had no effect on EFS-induced contraction in esophageal smooth muscle but the EFS-induced LES relaxation was dose-dependently inhibited by LPA. To identify the LPA receptor subtype that inhibits EFS-induced LES relaxation, we used the specific LPA(1)/LPA(3) antagonist Ki16425 and the LPA(3) agonist OMPT. Ki16425 significantly blocked the inhibitory effect of LPA on EFS-induced relaxation, but OMPT did not enhance the effect of LPA. These results suggest that LPA inhibits EFS-induced relaxation in LES via LPA(1) receptor-mediated signaling. It is well known that EFS-induced LES relaxation is related to the release of neurotransmitters, such as, nitric oxide, vasoactive intestinal polypeptide, and calcitonin gene-related peptide. We then investigated whether LPA selectively blocks NO-mediated signaling. Sodium nitroprusside-induced LES relaxation was found to be inhibited in the same manner as EFS-induced LES relaxation by LPA. This result suggests that LPA partially blocks NO uptake by presynaptic pathways, and thus, inhibits LES relaxation.

Nitric oxide activation of a potassium channel (BKCa) in feline lower esophageal sphincter

To assess the effect of nitric oxide (NO) on the large conductance potassium channel (BK(Ca)) in isolated circular (CM) and sling (SM) muscle cells and muscle strips from the cat lower esophageal sphincter (LES) to determine its regulation of resting tone and relaxation. Freshly enzymatically-digested and isolated circular smooth muscle cells were prepared from each LES region. To study outward K+ currents, the perforated patch clamp technique was employed. To assess LES resting tone and relaxation, muscle strips were mounted in perfused organ baths. (1) Electrophysiological recordings from isolated cells: (a) CM was more depolarized than SM (-39.7 ± 0.8 mV vs -48.1 ± 1.6 mV, P < 0.001), and maximal outward current was similar (27.1 ± 1.5 pA/pF vs 25.7 ± 2.0 pA/pF, P > 0.05); (b) The NO donor sodium nitroprusside (SNP) increased outward currents only in CM (25.9 ± 1.9 to 46.7 ± 4.2 pA/pF, P < 0.001) but not SM (23.2 ± 3.1 to 27.0 ± 3.4 pA/pF, P > 0.05); (c) SNP added in the presence of the BK(Ca) antagonist iberiotoxin (IbTX) produced no increase in the outward current in CM (17.0 ± 2.8 vs 13.7 ± 2.2, P > 0.05); and (d) L-NNA caused a small insignificant inhibition of outward K+ currents in both muscles; and (2) Muscle strip studies: (a) Blockade of the nerves with tetrodotoxin (TTX), or BK(Ca) with IbTX had no significant effect on resting tone of either muscle; and (b) SNP reduced tone in both muscles, and was unaffected by the presence of TTX or IbTX. Exogenous NO activates BK(Ca) only in CM of the cat. However, as opposed to other species, exogenous NO-induced relaxation is predominantly by a non-BK(Ca) mechanism, and endogenous NO has minimal effect on resting tone.

Cysteinyl Leukotriene Receptor Type 1 (CysLT 1) Mediates Contraction of the Guinea Pig Lower Esophageal Sphincter

Objective Leukotriene D 4 (LTD 4) causes contraction of the cat lower esophageal sphincter. The effects of leukotrienes in the guinea pig lower esophageal sphincter and the cysteinyl leukotriene receptor (CysLT) subtype that mediate this contraction are not known. The purpose of the present study was to characterize the CysLT receptors in the guinea pig lower esophageal sphincter. Materials and Methods We measured the contractions of transverse strips from the guinea pig lower esophageal sphincter caused by cysteinyl leukotrienes, LTC 4, LTD 4 and LTE 4, and the dihydroxy leukotriene, LTB 4. We also measured LTD 4-induced contraction inhibited by CysLT receptor antagonists, tetrodotoxin and atropine. Results In the guinea pig lower esophageal sphincter strips, LTC 4, LTD 4 and LTE 4, but not LTB 4, caused concentration-dependent contractions. The relative potencies for cysteinyl leukotrienes to cause contraction were LTD 4 = LTC 4 > LTE 4. LTE 4 was a partial agonist. The LTD 4-induced contraction was inhibited by two selective CysLT 1 receptor antagonists, montelukast and zafirlukast, and by the dual CysLT 1 and CysLT 2 receptor antagonist BAY u9773. The combination of both montelukast and BAY u9773 did not potentiate the inhibition caused by montelukast alone. These findings indicate that CysLT 1 mediates the contraction in the lower esophageal sphincter. Furthermore, LTD 4-induced contraction was not affected by tetrodotoxin or atropine, suggesting a direct effect. Conclusion These results demonstrate that cysteinyl leukotrienes, but not the dihydroxy leukotriene LTB 4, cause contraction of the guinea pig lower esophageal sphincter. The CysLT 1 receptor mediates this contraction.

Effect of hydrogen peroxide on VIP-induced relaxation of the cat lower esophageal sphincter

We investigated the effects of hydrogen peroxide (H2O2) on relaxation of the cat lower esophageal sphincter (LES). Vasoactive intestinal peptide (VIP) caused dose-dependent relaxation of LES, and H2O2 reduced VIP-induced relaxation. Relaxation was also attenuated by pertussis toxin (PTX), indicating a Gi/o component. VIP treatment increased [35S]GTPgammaS binding to Gs and Gi3 protein, but not to Go, Gq, Gil or Gi2. This increase in Gs or Gi3 binding was reduced by H2O2. However, the relaxation induced by sodium nitroprusside (SNP), 3-morpholino sydnomine (SIN-1), 8-br cGMP (cGMP analog), forskolin (adenylate cyclase activator), and dibutyryl-cAMP (a stable cAMP analog) was not reduced by H2O2. These data suggest that H202 inhibits VIP-induced relaxation via a Gi-dependent pathway, perhaps by inhibiting the activation of G(i3) or Gs downstream of the VIP receptor and independent of cAMP or NO-cGMP signaling.

Gastroesophageal Reflux Disease–Associated Esophagitis Induces Endogenous Cytokine Production Leading to Motor Abnormalities

Gastroesophageal reflux disease is a condition frequently associated with esophagitis and motor abnormalities. Recent evidence suggests that proinflammatory cytokines, such as interleukin (IL)-1beta and IL-6, may be implicated because they reduce esophageal muscle contractility, but these results derive from in vitro or animal models of esophagitis. This study used human esophageal cells and tissues to identify the cellular source of cytokines in human esophagitis investigate whether cytokines can be induced by gastric refluxate, and examine whether esophageal tissue- or cell-derived mediators affect muscle contractility. Endoscopic mucosal biopsy specimens were obtained from patients with and without esophagitis, organ-cultured, and undernatants were assessed for cytokine content. The cytokine profile of esophageal epithelial, fibroblast, and muscle cells was analyzed, and esophageal mucosa and cell products were tested in an esophageal circular muscle contraction assay. The mucosa of esophagitis patients produced significantly greater amounts of IL-1beta and IL-6 compared with those of control patients. Cultured esophageal epithelial cells produced IL-6, as did fibroblasts and muscle cells. Epithelial cells exposed to buffered, but not denatured, gastric juice produced IL-6. Undernatants of mucosal biopsy cultures from esophagitis patients reduced esophageal muscle contraction, as did supernatants from esophageal epithelial cell cultures. The human esophagus produces cytokines capable of reducing contractility of esophageal muscle cells. Exposure to gastric juice is sufficient to stimulate esophageal epithelial cells to produce IL-6, a cytokine able to alter esophageal contractility. These results indicate that classic cytokines are important mediators of the motor disturbances associated with human esophageal inflammation.

Electrically stimulated relaxation is not mediated by GABA in cat lower esophageal sphincter muscle

This study examined the effect of Gamma-Amino butyric acid (GABA) and selective GABA receptor related drugs on the electrically stimulated relaxation in the lower esophageal sphincter muscle (LES) of a cat. Tetrodotoxin (10(-6) M) suppressed the electrically stimulated (0.5-5 Hz) relaxation of the LES. However, guanethidine (10(-6) M) and atropine (10(-6) M) had no effect indicating that the relaxations were neurally mediated via the nonadrenergic and noncholinergic (NANC) pathways. NG-nitro-L-arginine methyl ester (10(-4) M, L-NAME) also inhibited the relaxant response but did not completely abolish the electrically stimulated relaxation with 60 % inhibition, which suggests the involvement of nitric oxide as an inhibitory transmitter. This study examined the role of GABA, an inhibitory neurotransmitter, on neurally mediated LES relaxation. GABA (10(-3)-10(-5) M, non selective receptor agonist), muscimol (10(-3)-10(-5) M, GABA-A agonist), and baclofen (10(-3)-10(-5) M, GABA-B agonist) had no significant effect on the electrically stimulated relaxation. Moreover, bicuculline (10(-5) M, GABA-A antagonist) and phaclofen (10(-5) M, GABA-B antagonist) had no inhibitory effect on the electrically stimulated relaxation. This suggests that GABA and the GABA receptor are not involved in the electrically stimulated NANC relaxation in the cat LES.

IL-1β signaling in cat lower esophageal sphincter circular muscle

In a cat model of acute experimental esophagitis, resting in vivo lower esophageal sphincter (LES) pressure and in vitro tone are lower than in normal LES, and the LES circular smooth muscle layer contains elevated levels of IL-1beta that decrease the LES tone of normal cats. We now examined the mechanisms of IL-1beta-induced reduction in LES tone. IL-1beta significantly reduced acetylcholine-induced Ca(2+) release in Ca(2+)-free medium, and this effect was partially reversed by catalase, demonstrating a role of H(2)O(2) in these changes. IL-1beta significantly increased the production of H(2)O(2), and the increase was blocked by the p38 MAPK inhibitor SB-203580, by the cytosolic phospholipase A(2) (cPLA(2)) inhibitor AACOCF3, and by the NADPH oxidase inhibitor apocynin, but not by the MEK1 inhibitor PD-98059. IL-1beta significantly increased the phosphorylation of p38 MAPK and cPLA(2). IL-1beta-induced cPLA(2) phosphorylation was blocked by SB-203580 but not by AACOCF3, suggesting sequential activation of p38 MAPK-phosphorylating cPLA(2). The IL-1beta-induced reduction in LES tone was partially reversed by AACOCF3 and by the Ca(2+)-insensitive PLA(2) inhibitor bromoenol lactone (BEL). IL-1beta significantly increased cyclooxygenase (COX)-2 and PGE(2) levels. The increase in PGE(2) was blocked by SB-203580, AACOCF3, BEL, and the COX-2 inhibitor NS-398 but not by PD-98059 or the COX-1 inhibitor valeryl salicylate. The data suggested that IL-1beta reduces LES tone by producing H(2)O(2), which may affect Ca(2+)-release mechanisms and increase the synthesis of COX-2 and PGE(2). Both H(2)O(2) and PGE(2) production depend on sequential activation of p38 MAPK and cPLA(2). cPLA(2) activates NADPH oxidases, producing H(2)O(2), and may produce arachidonic acid, converted to PGE(2) via COX-2.

H2O2: a mediator of esophagitis-induced damage to calcium-release mechanisms in cat lower esophageal sphincter

We previously reported that induction of acute experimental esophagitis by repeated perfusion of HCl may affect release of intracellular Ca(2+) stores. We therefore measured cytosolic Ca(2+) in response to a maximally effective dose of ACh in fura 2-AM-loaded lower esophageal sphincter (LES) circular muscle cells and examined the contribution of H(2)O(2) to the reduction in Ca(2+) signal. In normal cells, the ACh-induced Ca(2+) increase was the same in normal-Ca(2+) and Ca(2+)-free medium and was abolished by the phosphatidylinositol 4,5-bisphosphate-specific phospholipase C inhibitor U-73122, confirming that the initial ACh-induced contraction depends on Ca(2+) release from intracellular stores through production of inositol trisphosphate. In LES cells, the ACh-induced Ca(2+) increase in normal-Ca(2+) medium was significantly lower in esophagitis than in normal cells and was further reduced ( approximately 70%) when the cells were incubated in Ca(2+)-free medium. This reduction was partially reversed by the H(2)O(2) scavenger catalase. H(2)O(2) measurements in LES circular muscle showed significantly higher levels in esophagitis than in normal cells. When normal LES cells were incubated with H(2)O(2), the ACh-induced Ca(2+) increase was significantly reduced in normal-Ca(2+) and Ca(2+)-free medium and was similar to that observed in animals with esophagitis. The initial ACh-induced contraction was also reduced in normal cells incubated with H(2)O(2). H(2)O(2), when applied to cells at sufficiently high concentration, produced a visible and prolonged Ca(2+) signal in normal cells. H(2)O(2)-induced cell contraction was also sensitive to depletion of stores by thapsigargin (TG); conversely, H(2)O(2) reduced TG-induced contraction, suggesting that TG and H(2)O(2) may operate through similar mechanisms. Ca(2+)-ATPase activity measurement indicates that H(2)O(2) and TG reduced Ca(2+)-ATPase activity, confirming similarity of mechanism of action. We conclude that H(2)O(2) may be at least partly responsible for impairment of Ca(2+) release in acute experimental esophagitis by inhibiting Ca(2+) uptake and refilling Ca(2+) stores.

Inflammation induced changes in arachidonic acid metabolism in cat LES circular muscle

Myogenic lower esophageal sphincter (LES) tone is maintained by arachidonic acid metabolites, such as PGF(2alpha) and thromboxane A(2)/B(2). Experimental esophagitis in cat reduces LES in vivo pressure and in vitro tone. Because IL-1beta may mediate esophagitis-associated reduction in ACh release in esophagus, we examined whether IL-1beta may also play a role in esophagitis-induced reduction of LES tone. A cat model of experimental esophagitis was obtained by repeated esophageal perfusion with HCl (Biancani P, Barwick K, Selling J, and McCallum R. Gastreonterology 87: 8-16, 1984 and Sohn UD, Harnett KM, Cao W, Rich H, Kim N, Behar J, and Biancani P. J Pharmacol Exp Ther 283: 1293-1304, 1997.). LES circular muscle strips were examined in muscle chambers as previously described (Biancani P, Billett G, Hillemeier C, Nissenshon M, Rhim BY, Sweczack S, and Behar J. Gastroenterology 103: 1199-1206, 1992). Levels of inflammatory mediators were measured. IL-1beta levels were higher in esophagitis than in normal LES. IL-1beta reduced normal LES tone, and the reduction was reversed by catalase, suggesting a role of H(2)O(2). This was confirmed by IL-1beta-induced production of H(2)O(2) in normal LES and elevated H(2)O(2) levels in esophagitis. H(2)O(2) by itself is sufficient to explain the changes that occur in the muscle, reducing its ability to contract. H(2)O(2) increased PGE(2) in normal LES, and PGE(2) levels were elevated in esophagitis LES, whereas PGF(2alpha) levels were unchanged. H(2)O(2) also increased levels of 8-isoprostanes, stable prostaglandin-like compounds formed by free radical-induced peroxidation of arachidonic acid, and 8-isoprostane levels were elevated in esophagitis. The PGF(2alpha) analog 8-iso-PGF(2alpha) caused little contraction of LES strips but reduced PGF(2alpha) binding and contraction of normal LES. In esophagitis, PGF(2alpha) binding and contraction were reduced in LES, suggesting that isoprostanes may contribute to reduction in tone in esophagitis. The data suggest that, in esophagitis, IL-1beta causes production of H(2)O(2). H(2)O(2) increases PGE(2), which relaxes the LES, and 8-iso-F(2alpha), which blocks PGF(2alpha)-mediated contraction.

The alteration of intracellular signaling on the smooth muscle cells contraction in cat esophagitis

We investigated the alteration of signal transduction after acute esophagitis in cat lower esophageal sphincter (LES). Acute esophagitis (AE) was induced by perfusion with 0.1N HCl at a rate of 1 ml/min for 45 min over three consecutive days. Acetylcholine (ACh)-induced contraction was inhibited by M3>> M1 or M2 antagonists in normal LES. In AE, inhibition by M2 antagonists increased significantly, so that contraction was inhibited by M3> M2> M1 antagonists and the expression of M2 and M3 receptors were increased when compared to normal LES. In normal cells, ACh-induced contractions were antagonized by antibody against G q/11 and the phosphatidylinositol-specific phospholipase C (PI-PLC) antagonist, U73122. The phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor, D609, or the phospholipase D inhibitor, propranolol had no effects on contraction in normal LES. However, in AE, G q/11, and G i3 antibodies reduced ACh-induced contraction and U73122, propranolol and D609 also reduced the contraction. In AE, we found that the expressions of G protein subtypes were increased but the expression of PLCβ1, and PLCγ1 were decreased when compared to normal LES. In conclusion, experimental esophagitis may alter the signal transduction by ACh in LES. ACh-induced contraction is mediated by M3 receptor, G q/11 and PI-PLC in normal LES. However, in AE, the contractions are mediated by M2, M3 receptor, G q/11 and G i3. PC-PLC and PLD as PI-PLC are also involved in ACh-induced cell contraction in AE.

Calcium source diversity in feline lower esophageal sphincter circular and sling muscle.

Within muscular equivalents of cat lower esophageal sphincter (LES), the circular muscle develops greater spontaneous tone, whereas the sling muscle is more responsive to cholinergic stimulation. Smooth muscle contraction involves a combination of calcium release from stores and of calcium entry via several pathways. We hypothesized that there are differences in the sources of Ca(2+) used for contraction in sling and circular muscles and that these differences could contribute to functional asymmetry observed within LES. Contraction of muscle strips from circular and sling regions of LES was assessed in the presence of TTX. In Ca(2+)-free Krebs, tone was inhibited to a greater degree in circular than sling muscle. L-type Ca(2+) channel blockade with nifedipine or verapamil inhibited tone in LES circular but not sling muscle. Sarcoplasmic reticulum (SR) Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA) caused greater increase in tone in sling than in circular muscle. The phospholipase C inhibitor U-73122 and the SR inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] receptor blocker 2-aminoethoxydiphenyl borate (2-APB) inhibited tone in circular and sling muscles, demonstrating that continuous release of Ca(2+) from Ins(1,4,5)P(3)-sensitive stores is important in tone generation in both muscles. In Ca(2+)-free Krebs, ACh-induced contractions (AChC) were inhibited to a greater degree in sling than circular muscles. However, nifedipine and verapamil greatly inhibited AChC in the circular but not sling muscle. Depletion of SR Ca(2+) stores with CPA or inhibition of Ins(1,4,5)P(3)-mediated store release with either U-73122 or 2-APB inhibited AChC in both muscles. We demonstrate that LES circular and sling muscles 1) use intracellular and extracellular Ca(2+) sources to different degrees in the generation of spontaneous tone and AChC and 2) use different Ca(2+) entry pathways. These differences hold the potential for selective modulation of LES tone in health and disease.

Rho kinase and cat lower esophageal sphincter (LES) tone

Rho kinase and cat lower esophageal sphincter (LES) tone

Spontaneous tone and cholinergic contractions: Differences in calcium handling in cat lower esophageal sphincter sling and clasp muscles

Spontaneous tone and cholinergic contractions: Differences in calcium handling in cat lower esophageal sphincter sling and clasp muscles

Interaction of calmodulin- and PKC-dependent contractile pathways in cat lower esophageal sphincter (LES).

We have previously shown that, in circular muscle cells of the lower esophageal sphincter (LES) isolated by enzymatic digestion, contraction in response to maximally effective doses of acetylcholine (ACh) or Inositol Triphosphate (IP3) depends on the release of Ca2+ from intracellular stores and activation of a Ca2+-calmodulin (CaM)-dependent pathway. On the contrary, maintenance of LES tone, and response to low doses of ACh or IP3 depend on a protein kinase C (PKC) mediated pathway. In the present investigation, we have examined requirements for Ca2+ regulation of the interaction between CaM- and PKC-dependent pathways in LES contraction. Thapsigargin (TG) treatment for 30 min dose dependently reduced ACh-induced contraction of permeable LES cells in free Ca2+ medium. ACh-induced contraction following the low level of reduction of Ca2+ stores by a low dose of TG (10(-9) M) was blocked by the CaM antagonist, CGS9343B but not by the PKC antagonists chelerythrine or H7, indicating that the contraction is CaM-dependent. After maximal reduction in intracellular Ca2+ from Ca2+ stores by TG (10(-6) M), ACh-induced contraction was blocked by chelerythrine or H7, but not by CGS9343B, indicating that it is PKC-dependent. In normal Ca2+ medium, the contraction by ACh after TG (10(-9) M) treatment was also CaM-dependent, whereas the contraction by ACh after TG (10(-9) M) treatment was PKC-dependent. We examined whether PKC activation was inhibited by activated CaM. CGS 9343B inhibited the CaM-induced contraction, but did not inhibit the DAG-induced contraction. CaM inhibited the DAG-induced contraction in the presence of CGS 9343B. This inhibition by CaM was Ca2+ dependent. These data are consistent with the view that the switch from a PKC-dependent pathway to a CaM dependent pathway can occur and can be regulated by cytosolic Ca2+ in the LES.

Inflammation-induced changes in arachidonic acid metabolism in cat lower esophageal sphincter (LES)

Inflammation-induced changes in arachidonic acid metabolism in cat lower esophageal sphincter (LES)

Inflammation-induced changes in arachidonic acid metabolism in cat lower esophageal sphincter (LES)

Inflammation-induced changes in arachidonic acid metabolism in cat lower esophageal sphincter (LES)

Ultrastructural analysis of spinal primary afferent fibers within the circular muscle of the cat lower esophageal sphincter.

We have analyzed the ultrastructural characteristics and environment of spinal primary afferent fibers that run within the circular muscle of the cat lower esophageal sphincter. These were selectively labeled by anterogradely transported cholera toxin B subunit conjugated with horseradish peroxidase. Most of the labeled fibers were perpendicular to the muscle cells but some ran sinuously or parallel to the muscle cells. All the labeled fibers were unmyelinated and exhibited relatively rare varicosities. Most of the fibers were in large nerve fiber bundles surrounded by perineurium and probably project to the mucosa. Only some fibers that were in small nerve fiber bundles with no perineurium ran parallel to the musculature and established close relationships with smooth muscle cells. They might be a small subpopulation of the spinal tension receptors, most of the other spinal tension receptors being located in the myenteric plexus area, between the circular and longitudinal muscle.

Group I secreted PLA2 and arachidonic acid metabolites in the maintenance of cat LES tone.

Spontaneous tone of in vitro lower esophageal sphincter (LES) circular muscle is associated with elevated levels of arachidonic acid (AA), PGF(2alpha), and increased [35S]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to Gq-, Gi3-, and G(i1/i2)-like G proteins. Tone and AA levels were reduced by inhibitors of a pancreatic-like (group I) secreted phospholipase A2 (sPLA2), by the cyclooxygenase inhibitor indomethacin, and by the thromboxane A2 antagonist SQ-29548. In addition, pertussis toxin (PTX) reduced LES tone, confirming a role of PTX-sensitive G proteins in maintenance of LES tone. PGF(2alpha) contracted LES smooth muscle (strips and cells) and increased [35S]GTPgammaS binding to Gq and Gi3 in solubilized LES circular muscle membranes. PGF(2alpha)-induced contraction of LES permeable muscle cells was inhibited by Gq and Gi3 but not by G(i1/i2) and Go antibodies. The thromboxane A2 analog U-46619 contracted LES smooth muscle and increased Gq binding. U-46619-induced contraction was inhibited by Gq but not by Gi3, G(i1/i2), and Go antibodies. LES tone and [(35)S]GTPgammaS binding were significantly reduced by indomethacin. We conclude that group I sPLA2 may mediate "spontaneous" LES tone by producing AA, which is metabolized to PGF(2alpha) and thromboxane A2. These AA metabolites activate receptors linked to Gi3 and Gq to maintain LES contraction.

Corrigendum

Corrigendum

Non-adrenergic non-cholinergic neuron stimulation in the cat lower esophageal sphincter

Both electrical field stimulation and nicotine produced non-adrenergic non-cholinergic (NANC) relaxation of the circular muscle strips from the cat lower esophageal sphincter in the presence of 5 μM guanethidine and 5 μM scopolamine. Low-frequency stimulation (2 Hz, 0.2 ms duration, supramaximal current intensity, 20-s train) provoked a transient relaxation, while at high-frequency stimulation (20 Hz) a slow restoration to the resting tone was observed. Blockade of nitric oxide (NO) synthesis by 1 mM N ω-nitro- l-arginine decreased by 20% the amplitude of the 20 Hz-induced relaxation and changed the pattern of relaxation, making it similar to the sustained relaxation evoked by exogenously applied vasoactive intestinal peptide (VIP). After chymotrypsin (4 U/ml), the pattern of the high-frequency-induced relaxation resembled that of the low-frequency-induced relaxation. Similarly, chymotrypsin changed the shape of nicotine-provoked relaxation, increasing the speed of restoration to the resting tone. We suggest that the fast relaxation elicited in cat lower esophageal sphincter by electrical field stimulation or nicotine is initiated by NO. The slow restoration to the resting tone in the case of high-frequency- or nicotine-induced relaxation seems to be due to the release of VIP or VIP-like peptides. The possibility of participation of another transmitter(s) involved in NANC relaxation should not be excluded.