Nonadrenergic, noncholinergic relaxation in longitudinal muscle of rat jejunum

The Inhibitory Mechanism of Gentamicin on Electrical Field Stimulation Response in Rat Bladder Smooth Muscle

To see the inhibitory mechanism of gentamicin in response to electrical field stimulation (EFS) using the rat bladder smooth muscle, atropine or guanethidine was treated but had no effect. Methylsergide, a non-selective 5-HT1, 5-HT2 receptor antagonist was also treated but had on effect. Kinase inhibitors, such as chelerythrine (PKC inhibitor), ML-9 (MLCK inhibitor), or Y27632 (rho kinase inhibitor) were pretreated before gentamicin treatment, but did not have effect. For U73122, a phospholipase C (PLC) inhibitor however, the inhibitory effect to gentamicin was significantly attenuated in all frequencies given by the EFS. Therefore gentamicin induced inhibitory effect on EFS response in rat bladder smooth muscle was not mediated by the activation of adrenergic, cholinergic, or serotonergic receptor. The inhibition of gentamicin might be mediated through the PLC dependent pathway, but not through the PKC, MLCK or rho kinase dependent pathway.

Effect of GABA-ergic mechanisms on synaptosomal NO synthesis and the nitrergic component of NANC relaxation in rat ileum

BACKGROUND

γ-Aminobutyric acid (GABA) acts on specific neural receptors [A, B and C(Aρ)] to modulate gastrointestinal function. The precise role of GABA receptor activation in the regulation of presynaptic nitric oxide (NO) synthesis in nerve terminals is unknown.

METHODS

Rat ileal nerve terminals were isolated by differential centrifugation. Nitric oxide synthesis was analysed using a L-[(3) H]arginine assay. In vitro studies were performed under non-adrenergic non-cholinergic (NANC) conditions on isolated ileal segments.

KEY RESULTS

γ-Aminobutyric acid inhibited NO synthesis significantly (n = 6, P < 0.05) [(fmol mg(-1) min(-1)) control: 27.7 ± 1.5, 10(-6) mol L(-1): 19.7 ± 1.3; 10(-5) mol L(-1): 17.5 ± 3.0]. This effect was antagonized by the GABA A receptor antagonist bicuculline and the GABA C receptor antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), but not by the GABA B receptor antagonist SCH 50911. The GABA A receptor agonist muscimol [(fmol mg(-1) min(-1)) control: 27.6 ± 1.0, 10(-6) mol L(-1): 19.1 ± 1.7, n = 5, P < 0.05] and the GABA C receptor agonist cis-4-aminocrotonic acid (CACA) [(fmol mg(-1) min(-1)) control: 29.5 ± 3.2, 10(-3) mol L(-1): 20.3 ± 2.5, n = 6, P < 0.05], mimicked the GABA-effect, whereas the GABA B agonist baclofen was ineffective. Bicuculline reversed the inhibitory effect of muscimol, TPMPA antagonized the effect of CACA. In functional experiments the GABA A and C receptor agonists reduced the NANC relaxation induced by electrical field stimulation in rat ileum by about 40%. After NOS-inhibition by Nε-nitro-L-arginine methyl ester (L-NAME) the GABA A receptor agonist had no effect, whereas the GABA C receptor agonist still showed a residual response.

CONCLUSIONS & INFERENCES

γ-Aminobutyric acid inhibits neural NO synthesis in rat ileum by GABA A and GABA C(Aρ) receptor-mediated mechanisms.

Age-related changes in functional NANC innervation with VIP and substance P in the jejunum of Lewis rats

Age-related changes in non-adrenergic, non-cholinergic (NANC) neurotransmission might contribute to differences in gastrointestinal motility. Our aim was to determine age-related changes in functional innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunum. We hypothesized that maturation causes changes in neurotransmission with these two neuropeptides. Longitudinal and circular jejunal muscle strips from young (3 months) and middle-aged (15 months) rats (total: 24 rats) were studied; the response to exogenous VIP and Sub P and the effect of their endogenous release from the enteric nervous system during electrical field stimulation (EFS) were evaluated. In longitudinal muscle, response to exogenous VIP and endogenously released VIP during EFS were increased in middle-aged rats, while the effect of endogenously released Sub P was decreased. In the circular muscle, the response to endogenously released VIP was increased in middle-aged rats, while the effects of exogenous VIP and endogenously released Sub P were unchanged. Response to exogenous Sub P was unaffected by maturation in both muscle layers. Spontaneous contractile activity was increased in the longitudinal and circular muscle of the older rats. In the jejunum of middle-aged rats, participation of VIP in functional NANC innervation was increased, while functional innervation with Sub P was decreased. These changes in the balance of inhibitory and excitatory neurotransmission occur during the year of maturation in rats and demonstrate an age-dependant plasticity of neuromuscular bowel function.

Small intestinal motility in soluble guanylate cyclase alpha1 knockout mice: (Jejunal phenotyping of sGCalpha1 knockout mice)

Nitric oxide (NO) activates soluble guanylate cyclase (sGC) to produce guanosine-3',5'-cyclic-monophosphate (cGMP). The aim of this study was to investigate the nitrergic regulation of jejunal motility in sGCalpha(1) knockout (KO) mice. Functional responses to nitrergic stimuli and cGMP levels in response to nitrergic stimuli were determined in circular muscle strips. Intestinal transit was determined. Nitrergic relaxations induced by electrical field stimulation and exogenous NO were almost abolished in male KO strips, but only minimally reduced and sensitive to ODQ in female KO strips. Basal cGMP levels were decreased in KO strips, but NO still induced an increase in cGMP levels. Transit was not attenuated in male nor female KO mice. In vitro, sGCalpha(1)beta(1) is the most important isoform in nitrergic relaxation of jejunum, but nitrergic relaxation can also occur via sGCalpha(2)beta(1) activation. The latter mechanism is more pronounced in female than in male KO mice. In vivo, no important implications on intestinal motility were observed in male and female KO mice.

Effects of extrinsic denervation on innervation with VIP and substance P in circular muscle of rat jejunum

Extrinsic denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine changes in nonadrenergic, noncholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunal circular muscle after SBT. Muscle strips were studied in tissue chambers from six groups of rats (n > or = 6 per group): naïve controls (NC), animals 1 week after anaesthesia/sham celiotomy (SC-1), and 1 and 8 weeks after jejunal and ileal transection/reanastomosis (TA-1, TA-8) and after syngeneic, orthotopic SBT (SBT-1, SBT-8). Response to exogenous VIP and Sub P and their endogenous release during electrical field stimulation (EFS) were studied. Exogenous VIP and Sub P caused a dose-dependent inhibition and stimulation of mechanical activity in all groups respectively (P < 0.05). The responses to VIP and Sub P were decreased (compared to NC) in all groups at 1 and 8 weeks postoperatively. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) did not prevent the inhibition by exogenous VIP in any group, while the Sub P antagonist ([D-Pro(2),D-Trp(7,9)]-Sub P) prevented the effect of exogenous Sub P in NC, TA-8 and SBT-8 (P < 0.05). Responses to exogenous VIP were unaffected by the nitric oxide synthase inhibitor l-N(G)-nitro arginine and precontraction of muscle strips with Sub P. Endogenous release of VIP and Sub P during EFS was preserved after SBT. In circular muscle of rat jejunum, changes in neuromuscular transmission with VIP and Sub P during the first 8 weeks after SBT are not mediated by extrinsic denervation.

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long-term effects of extrinsic denervation on functional non-adrenergic, non-cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age-matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently in both groups, greater in NC than in SBT. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor l-N(G)-nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than in SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and increased the EFS-induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Long-term effects of extrinsic denervation on VIP and substance P innervation in circular muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine long-term effects of extrinsic denervation on function of nonadrenergic, noncholinergic innervation with substance P and vasoactive intestinal polypeptide (VIP). Contractile activity of jejunal circular muscle strips from six age-matched, naive control rats (NC) and eight rats 1 year after syngeneic SBT was studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently to a comparable degree in both groups. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor L-NG-nitro-arginine did not affect VIP-induced inhibition but increased contractile activity during electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and decreased the excitatory EFS response. Immunohistofluorescence showed tyrosine hydroxylase staining after SBT indicating sympathetic reinnervation. In jejunal circular muscle after chronic denervation, response to exogenous substance P, but not VIP, is decreased, whereas endogenous release of both neurotransmitters is preserved. Alterations in balance of excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Role of VIP and Substance P in NANC Innervation in the Longitudinal Smooth Muscle of the Rat Jejunum—Influence of Extrinsic Denervation

BACKGROUND

This study was designed to determine changes in nonadrenergic, noncholinergic (NANC) neurotransmission mediated by Vasoactive Intestinal Polypeptide (VIP) and Substance P after small bowel transplantation (SBT).

MATERIALS AND METHODS

Six groups of rats (n > or = 6 per group) were studied: naïve controls (NC); 1 wk after anesthesia/sham celiotomy (SC-1); 1 or 8 wk after jejunal and ileal transection/reanastomosis (TA-1, TA-8), or syngeneic, orthotopic SBT (SBT-1, SBT-8). Jejunal longitudinal muscle strips were studied under NANC-conditions for spontaneous contractile activity, response to exogenous VIP and Substance P, and electrical field stimulation (EFS).

RESULTS

Spontaneous activity did not differ between the six groups. VIP inhibited contractile activity in all groups 1 wk postoperatively (P < 0.05), which was prevented by the NO synthase inhibitor L-N(G)-nitro arginine (L-NNA). In contrast, VIP had no effect in the other groups. Precontraction with Substance P exposed an inhibitory effect of VIP in all groups (P < 0.05 each). Substance P increased contractile activity in all groups, but to a lesser extent in SBT-8 compared with NC, TA-8, and SBT-1 (P < 0.05). The inhibitory effect of EFS at 6 Hz was prevented by L-NNA in NC and TA-8; addition of the VIP antagonist ([D-p-Cl-Phe(6), Leu(17)]-VIP) increased contractile activity in NC, but not in TA-8 and SBT-8. The Substance P antagonist ([D-Pro(2), D-Trp(7,9)]-Substance P) decreased contractile activity during EFS at 50 Hz in NC and SBT-8.

CONCLUSIONS

SBT decreased response to exogenous Substance P, although release of endogenous Substance P (EFS) is preserved. Changes in VIP signaling are acute and reversible and not caused by effects of SBT.

P2 purinoceptor antagonists inhibit the non-adrenergic, non-cholinergic relaxation of the human colon in vitro

Neurotransmitters released by myenteric neurons regulate movements of intestinal smooth muscles. There has been little pharmacological evidence for a role of purinergic mechanisms in the non-adrenergic, non-cholinergic (NANC) relaxation of the human large intestine. We used P(2) purinoceptor antagonists to assess whether such receptors are involved in the NANC relaxation of the circular muscle of the human sigmoid colon. It was also investigated whether the guanylate cyclase enzyme mediates the NANC response. Human colonic circular strips were tested in organ bath experiments with isotonic recording. NANC, non-nitrergic relaxations induced by electrical field stimulation (1 and 10 Hz, in the presence of atropine, guanethidine, and 100 microM N(G)-nitro-L-arginine [L-NOARG]) were strongly inhibited by a combination of the P(2) purinoceptor antagonists pyridoxal-phosphate-6-azophenyl-2',4'-sulfonic acid (PPADS) (50 microM) and suramin (100 microM). PPADS plus suramin was ineffective in the absence of L-NOARG. L-NOARG alone significantly reduced the NANC relaxation to electrical stimulation. PPADS plus suramin strongly inhibited the relaxation in response to exogenous alpha,beta-methylene ATP. The guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (3 microM) inhibited the NANC relaxation, but did not add to its reduction by L-NOARG. L-NOARG was still slightly effective in the presence of ODQ. Vasoactive intestinal polypeptide tachyphylaxis failed to influence the non-nitrergic NANC relaxation. It is concluded that nitric oxide (NO) and ATP co-mediate, in a non-additive manner, the NANC relaxation. NO probably acts through the guanylate cyclase, though a small fraction of its effect might be mediated by other mechanisms. Activators of the guanylate cyclase other than NO do not seem to participate in the NANC relaxation.

Activation of 5-HT3 receptors in the rat and mouse intestinal tract: a comparative study

This study provides a comprehensive evaluation of 5-HT(3) receptor functional distribution in both the rat and mouse intestinal tract. 5-HT(3A-S) receptor splice variant mRNA was expressed throughout the intestine of the rat and mouse; the 5-HT(3A-L) variant being more common in the rat.5-HT, m-CPB, 1-PBG and 2-methyl-5-hydroxytryptamine (2m5-HT) induced contraction in the jejunum, ileum, proximal colon and distal colon of the rat (pEC(50) range: 2m5-HT, 5.86+/-0.40 to m-CPB, 7.47+/-0.27) and mouse (pEC(50) range: 1-PBG, 5.34+/-0.06 to m-CPB, 6.49+/-0.14) in the presence of nontarget 5-HT receptor antagonists, methysergide (1 muM) and GR125487 (0.1 microM). The rank orders of potency in the four regions of the rat and mouse intestine were concordant with the accepted order and the responses to 5-HT were inhibited by ondansetron (0.1 microM).5-HT(3)-induced contractions to 5-HT were reduced by tetrodotoxin (1 microM). Pargyline (10 muM) and fluoxetine (1 microM) potentiated responses in the rat jejunum. Atropine (0.1 microM) potentiated 5-HT(3)-induced responses in the rat jejunum (E(max) 49-65%), but attenuated responses in most other regions of the rat and mouse (e.g. mouse ileum: E(max) 57-26%). In the rat jejunum, L-NAME (100 microM) mimicked the effect of atropine, hexamethonium (100 microM) suppressed 5-HT(3)-induced responses, but tachykinin receptor antagonists were without effect. It is concluded that functional 5-HT(3) receptors are present in nerves along the length of the rat and mouse intestinal tract. The mouse proximal colon was found to discriminate 5-HT(3) receptor agonist profiles better than any other region in the rat or mouse. The rat jejunum shows evidence of 5-HT uptake and inactivation processes as well as inhibitory nitrergic and nontachykinin excitatory pathways associated with the 5-HT(3)-induced response.

P2 purinoceptors account for the non-nitrergic NANC relaxation in the rat ileum

The transmitters involved in the non-nitrergic component of the non-adrenergic, non-cholinergic (NANC) inhibitory response of the rat small intestinal longitudinal muscle to electrical field stimulation of its nerves is a matter of controversy. The present study is the first one to utilise a combination of a nitric oxide synthase inhibitor and a P(2) purinoceptor antagonist for studying this response. We found that the P(2) purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 5x10(-5) M) abolished the non-nitrergic NANC relaxation to electrical field stimulation (10 Hz). PPADS alone provided a significant, moderate inhibitory action. PPADS specifically inhibited relaxations due to exogenous adenosine 5'-triphosphate (ATP) or alpha,beta-methylene ATP. The guanylate cyclase blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10(-6) M) did not add to the inhibitory action of N(G)-nitro-L-arginine on field stimulation-induced relaxation. ODQ abolished the relaxant effect of the nitric oxide donors nitroglycerin or sodium nitroprusside. These data indicate that: (1) nitric oxide and ATP fully account for the field stimulation-induced relaxation in the rat ileal strip under the experimental conditions of this study, and (2) no ODQ-sensitive guanylate cyclase-mediated mechanism is involved in the non-nitrergic component of the NANC relaxation.

Participation of ATP in nonadrenergic, noncholinergic relaxation of longitudinal muscle of wistar rat jejunum

A role of ATP in nonadrenergic, noncholinergic (NANC) relaxations was examined in the Wistar rat jejunum. Electrical field stimulation (EFS) induced NANC relaxation of longitudinal muscle of the jejunal segments in a frequency-dependent manner. A purinoceptor antagonist, adenosine 3'-phosphate 5'-phosphosulfate (A3P5PS, 100 muM) inhibited the relaxation: relaxations induced by EFS at lower or higher frequencies were either completely or partially inhibited, respectively. After the jejunal segments had been desensitized to ATP, the relaxations were decreased to the same extent as those inhibited by A3P5PS. An inhibitor of small conductance Ca(2+)-activated K(+) channels (SK channels), apamin (100 nM), completely inhibited EFS-induced relaxations. Treatment of the segments with an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, thapsigargin (1 muM), significantly inhibited the relaxations. The exogenous ATP-induced relaxation of longitudinal muscle occurred with a concomitant decrease in intracellular Ca(2+) levels. Apamin and thapsigargin abolished these ATP-induced responses. A3P5PS significantly inhibited the inhibitory junction potentials which were induced in the longitudinal muscle cells. In addition, apamin significantly inhibited the hyperpolarization that was induced by exogenous ATP in the cells. These findings in the Wistar rat jejunum suggest that ATP participates in the NANC relaxation via activation of SK channels induced by Ca(2+) ions that are released from the thapsigargin-sensitive store site.

Inhibitory pathways in the circular muscle of rat jejunum

1. Conflicting data have been reported on the contribution of nitric oxide (NO) to inhibitory neurotransmission in rat jejunum. Therefore, the mechanism of relaxation and contribution to inhibitory neurotransmission of NO, adenosine 5'-triphosphate (ATP), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) was examined in the circular muscle of Wistar-Han rat jejunum. 2. Mucosa-free circular muscle strips were precontracted with methacholine in the presence of guanethidine and exposed to electrical field stimulation (EFS) and exogenous NO, ATP, VIP and PACAP. All stimuli induced reduction of tone and inhibition of phasic motility. Only electrically induced responses were sensitive to tetrodotoxin (3 x 10(-6) m). 3. NO (10(-6)-10(-4) m)-induced concentration-dependent relaxations that were inhibited by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ; 10(-5) m) and the small conductance Ca(2+)-activated K(+)-channel blocker apamin (APA; 3 x 10(-8) m). 4. Relaxations elicited by exogenous ATP (10(-4)-10(-3) m) were inhibited by the P2Y purinoceptor antagonist reactive blue 2 (RB2; 3 x 10(-4) m), but not by APA and ODQ. 5. The inhibitory responses evoked by 10(-7) m VIP and 3 x 10(-8) m PACAP were decreased by the selective PAC(1) receptor antagonist PACAP(6-38) (3 x 10(-6) m) and APA. The VPAC(2) receptor antagonist PG99-465 (3 x 10(-7) m) reduced relaxations caused by VIP, but not those by PACAP, while the VPAC(1) receptor antagonist PG97-269 (3 x 10(-7) m) had no influence. 6. EFS-induced relaxations were inhibited by the NO-synthase inhibitor N(omega)-nitro-l-arginine methyl ester (3 x 10(-4) m), ODQ and APA, but not by RB2, PG97-269, PG99-465 and PACAP(6-38). 7. These results suggest that NO is the main inhibitory neurotransmitter in the circular muscle of Wistar-Han rat jejunum acting through a rise in cyclic guanosine monophosphate levels and activation of small conductance Ca(2+)-dependent K(+) channels.

Localization of Ca2+-activated K+ channel, SK3, in fibroblast-like cells forming gap junctions with smooth muscle cells in the mouse small intestine

In the present study, we examined the expression and the localization of apamin-sensitive small conductance Ca(2+)-activated K(+) channels (SK channels) in the mouse intestine. SK3-immunoreactivity (IR) was detected in both ileum and colon. Double staining experiments showed that SK3-IR was colocalized with prolyl 4-hydroxylase (PH(alpha))-IR, but not with c-Kit-IR which are markers of fibroblast cells and the interstitial cells of Cajal (ICC), respectively. Although SK3-IR was colocalized with vimentin-IR, which is another marker of ICC, the reactivity of SK3-immunopositive cells was weaker than that of ICC. The SK3-immunopositive cells were similarly present in the intestine of c-Kit mutant mice (W/W(V)), in which ICC were absent, and its wild-type mice. The immuno-electron microscopic analysis indicated that SK3 was localized in the cells that had some similar morphological features to ICC, but obviously different from ICC. The SK3-immunopositive cells had gap junctions with the smooth muscle cells. The gap junctions were smaller than those between ICC and smooth muscle cells. These results indicate expression of SK3 in fibroblast-like cells, but not in ICC, and suggest participation of the cells in the intestinal motility.

Involvement of a purinergic pathway in the sympathetic regulation of motility in rat ileum

We investigated extrinsic neuronal regulation of intestinal motility. The mesenteric nerve stimulation (MNS; duration 0.5 ms, 10 Hz for 30 s) evoked relaxation in the longitudinal muscle direction of the isolated rat ileum. The MNS-induced relaxation was abolished by guanethidine (2 microM) or propranolol (10 microM), but was not affected by prazosin (10 microM), rauwolscine (10 microM), hexamethonium (100 microM) or capsaicin (1 microM). Exposure to a high concentration (100 microM) of ATP (ATP-desensitization) or ADP (ADP-desensitization) reduced the MNS-induced relaxation to 44.7% or 32.5% of the control (P<0.01), respectively. P2 purinoceptor antagonists [suramin (100 microM) and reactive blue-2 (RB-2, 50 microM)] or small conductance Ca(2+)-activated K(+) channel blocker, apamin (0.5 microM), significantly decreased the relaxation to 54.4% and 25.6% or 19.4% of the control (P<0.01), respectively, whereas selective P2Y(1) purinoceptor antagonist MRS2179 (10 microM) failed to affect the relaxation. Furthermore, exogenous ATP (1 microM) or ADP (1 microM) elicited relaxation in the rat ileum, which was almost abolished by reactive blue-2 (50 microM, 9.1% of control remained, P<0.05). In contrast, relaxation induced by noradrenalin (10 microM) was not antagonized by ATP-desensitization, apamin (0.5 microM) or reactive blue-2 (50 microM). From the present results, we conclude that noradrenergic sympathetic nerves might regulate intestinal motility mediated through a purinergic inhibitory neuronal pathway in the rat small intestine.

A possible role of neurotensin in NANC relaxation of longitudinal muscle of the jejunum and ileum of Wistar rats

The mediators of nonadrenergic, noncholinergic (NANC) relaxation in longitudinal muscle of the jejunum and ileum of Wistar rats were examined in vitro. Treatment of the jejunal and ileal segments with alpha-chymotrypsin resulted in decreases in the NANC relaxations induced by electrical field stimulation (EFS) by about one half. The NANC relaxations were also decreased by about one half after the segments had been desensitized to neurotensin. A neurotensin receptor antagonist, SR48692 (10 microM) inhibited the NANC relaxation by 56 and 34% in the jejunal and ileal segments, respectively. An inhibitor of small conductance Ca2+ -activated K+ channel (SK channel), apamin (100 nM) also inhibited the NANC relaxation by 83 and 63%, respectively. Exogenous neurotensin-induced relaxations of the two segments were abolished by apamin. In the ileal segments, N(G)-nitro-L-arginine (L-NOARG, 100 micro M), inhibited the NANC relaxation by 43%. L-NOARG, but not apamin, further inhibited the relaxation which persisted after the desensitization to neurotensin. Apamin with SR48692 inhibited the relaxation only to the same extent as apamin alone. EFS induced inhibitory junction potentials (i.j.ps) in the longitudinal muscle cells of the ileum. I.j.ps consisted of a rapid and a delayed phase. L-NOARG significantly inhibited only the delayed phase. EFS induced only a rapid i.j.ps in the jejunum. SR48692 and apamin inhibited the i.j.ps. These findings suggest that neurotensin and unknown substance(s) mediate NANC relaxation via SK channels in the jejunum of Wistar rats, and that neurotensin via SK channels and nitric oxide not via SK channels separately mediate the relaxation in the ileum.

Expression of Ca(2+)-activated K(+) channels, SK3, in the interstitial cells of Cajal in the gastrointestinal tract

A role for small-conductance Ca(2+)-activated K(+) (SK) channels on spontaneous motility of the gastrointestinal tract has been suggested. Although four subtypes of SK channels were identified in mammalian tissues, the subtypes of SK channel expressed in the gastrointestinal tract are still unknown. In this study, we investigated the expression and localization of SK channels in the gastrointestinal tract. RT-PCR analysis shows expression of SK3 and SK4 mRNA, but not SK1 or SK2 mRNA, in the rat intestine. SK3 immunoreactivity was detected in the myenteric plexus and muscular layers of the stomach, ileum, and colon. SK3-immunoreactive cells were stained with antibody for c-kit, a marker for the interstitial cells of Cajal (ICC), but not with that for glial fibrillary acidic protein in the ileum and stomach. Immunoelectron microscopic analysis indicates that SK3 channels are localized on processes of ICC that are located close to the myenteric plexus between the longitudinal and circular muscle layers and within the muscular layers. Because ICC have been identified as pacemaker cells and are known to play a major role in generating the regular motility of the gastrointestinal tract, these results suggest that SK3 channels, which are expressed specifically in ICC, play an important role in generating a rhythmic pacemaker current in the gastrointestinal tract.

Stereologic description of the changing expression of constitutive nitric oxide synthase and heme oxygenase in the enteric plexuses of the pig small intestine during development

The similarities between heme oxygenase-2 (HO-2) and nitric oxide synthase (nNOS) and the transient expression of nNOS during development led us to investigate whether both systems are similarly affected by changes that occur during development and by regional differences along the small intestine. By combining NADPH diaphorase histochemistry and HO-2 immunohistochemistry on whole-mount preparations and by using stereologic methods, a qualitative and quantitative description of HO-2 and nNOS expression was obtained. Examinations were carried out on the small intestine of fetal, 1-2-day and 5-6-week-old pigs. In all age groups, three enteric plexuses were distinguished. The presence of HO-2-immunoreactive (HO-2-IR) and NADPH diaphorase-positive neurons corresponded to earlier morphological and physiological reports. Nevertheless, the total number of nitrergic neurons remained constant or decreased in the enteric plexuses, whereas the total number of HO-2-IR neurons displayed an overall increase. Changing concentrations of glucocorticoids, target-derived signals, presynaptic input, and an effect of HO-2 activity on nNOS synthesis are likely to play roles in the observed developmental changes. The numerical density of HO-2-IR neurons remained relatively constant along the intestinal tract; in contrast, the nitrergic neurons were most numerous in the inner submucous and myenteric plexus in the duodenum and ileum, respectively. It is believed that the duodenal nitrergic neurons in the inner submucous plexus could be involved in the regulation of duodenal secretion processes, whereas the region-dependent density in the myenteric plexus possibly forms the morphological basis for a regionally different participation of NO in the relaxation of the small intestine.

Increase in participation of vasoactive intestinal peptide in relaxation of the distal colon of Wistar rats with age

Changes in participation of vasoactive intestinal peptide (VIP) in nonadrenergic noncholinergic (NANC) relaxation of longitudinal muscle of the distal colon with age were studied in 2- to 50-week-old Wistar rats in vitro. The extent of the VIP-mediated component of the relaxation induced by electrical field stimulation (EFS) was determined by the effect of VIP(10 - 28), a VIP receptor antagonist. In 2-week-old rats, the extent of the VIP-mediated component of the relaxation was scarce, about 10%, whereas the component gradually increase with age and reached the maximum extent 66% at 50-week-old. Since our previous results suggest that VIP induces NANC relaxation via activation of charybdotoxin (ChTx, a blocker of large conductance Ca(2+)-activated K(+) channel)-sensitive K(+) channels with concomitant slow hyperpolarization in the muscle cells, we next studied whether ChTx-sensitive component and slow hyperpolarization changes with age. Extent of ChTx-sensitive component of the relaxation increased with age, showing a very similar pattern to VIP-mediated one. EFS induced monophasic inhibitory junction potentials (i.j.ps) in longitudinal muscle cells of the distal colon of 2- and 4-week-old. EFS also induced biphasic i.j.ps in many longitudinal muscle cells of 8- and 50-week-old: rapid and subsequent slow hyperpolarization. A VIP receptor antagonist selectively inhibited the slow hyperpolarization. Exogenously added VIP induced no appreciable change in the membrane potential of longitudinal muscle cells of 2-week-old, whereas it induced slight slow hyperpolarization of the cell membrane in 4-week-old and magnitude of the hyperpolarization increased with age. On the other hand, relaxant response of the longitudinal muscle to exogenously added VIP was high in younger rats. The present results suggest that the role of VIP in mediating NANC relaxation of longitudinal muscle of the Wistar rat distal colon is very little at neonatal stage, but it increases with age.

Nitrergic and purinergic regulation of the rat pylorus

The role of nitric oxide (NO) and ATP in the regulation of nonadrenergic, noncholinergic (NANC) inhibitory transmission in the pylorus remains unclear. In the presence of atropine and guanethidine, electric field stimulation induced NANC relaxations in a frequency-dependent manner (1-20 Hz) in the rat pylorus. NANC relaxations were significantly inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M). P(2X) purinoceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 3 x 10(-5) M) and P(2Y) purinoceptor antagonist reactive blue 2 (2 x 10(-5) M) had no effect on NANC relaxations. However, the combined administration of L-NAME and PPADS, but not reactive blue 2, evoked greater inhibitory effects on NANC relaxation than that evoked by L-NAME alone. alpha-Chymotrypsin and vasoactive intestinal polypeptide antagonist did not affect NANC relaxations. ATP (10(-5)-10(-3) M) and P(2X) purinoceptor agonist alpha, beta-methyleneadenosine 5'-triphosphate (10(-7)-10(-5) M), but not P(2Y) purinoceptor agonist 2-methylthioadenosine 5'-triphosphate (10(-7)-10(-5) M), induced muscle relaxations in a dose-dependent manner, and relaxations were significantly reduced by PPADS and unaffected by TTX. These studies suggest that NO and ATP act in concert to mediate NANC relaxation of the rat pylorus. ATP-induced relaxation appears to be mediated by P(2X) purinoceptors located on smooth muscle cells.

Mediators of nonadrenergic, noncholinergic relaxation in Sprague Dawley rat intestine: comparison with the mediators of other strains

Participation of nitric oxide, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) in nonadrenergic, noncholinergic (NANC) relaxation of longitudinal muscle of various intestinal regions in Sprague Dawley rats (8-week-old) was studied in vitro. Nitric oxide was suggested to participate in NANC relaxation of every intestinal region studied. But the participation was partial and its extent varied among the regions: significant in the proximal colon and rectum, and moderate in the jejunum, ileum and distal colon. Participation of PACAP in NANC relaxation was suggested only in the distal colon, while that of VIP was not detected in any of regions. Results obtained in the present study indicate that extent of participation of nitric oxide in NANC relaxation in Sprague Dawley rat intestine is more significant than those of other strains, Wistar and Wistar-ST.

Functional antagonism between nitric oxide and ATP in the motor responses of guinea-pig ileum

1. The interaction of nitric oxide and ATP in the non-adrenergic, non-cholinergic (NANC) motor responses and the presence of NADPH-diaphorase and quinacrine-positive myenteric neurones were studied on guinea-pig ileum using mechanographic, histochemical and quinacrine-fluorescence techniques. In the presence of phentolamine, propranolol and atropine, the non-precontracted longitudinally oriented organ bath preparations responded to sodium nitroprusside (1-100 microM) or ATP (5-50 microM) with tetrodotoxin (0.1 microM)-resistant relaxation or contraction, respectively. The effects of ATP were suramin (50 microM)- and apamin (5 microM)-sensitive. 2. The NANC motor responses elicited by electrical stimulation (0.8 ms, 1-20 Hz, 20 s) consisted of tetrodotoxin-sensitive relaxation phase followed by a phase of twitch-like and tonic contractions. 3. NG-nitro-L-arginine (L-NNA, 0.1-0.5 mM) inhibited or abolished the relaxation phase. L-arginine (0.5 mM), but not D-arginine (0.5 mM), restored the relaxation phase in L-NNA-pretreated preparations. The relaxation phase increased after ATP-induced desensitization of purinoceptors and in the presence of suramin (50 mciroM) but was abolished by apamin (5 microM). 4. The phase of contractions was enhanced by L-NNA (0.1-0.5 mM) and restored by L-arginine (0.5 mM). The twitch-like and tonic contractions were decreased during ATP-induced purinoceptor desensitization and in the presence of suramin (50 microLM). Apamin (5 microM) inhibited the tonic contractions. 5. The desensitization of purinoceptors by ATP did not change the L-NNA-induced inhibition of the relaxation phase but decreased the L-NNA-increased phase of contractions. L-NNA reduced the relaxation phase and increased the phase of contractions during purinoceptor desensitization. 6. We conclude that in the longitudinal muscle layer of the guinea-pig ileum, nitric oxide mediates the relaxation phase while ATP contributes via smooth muscle P2 purinoceptors to the phase of contractions suggesting a postjunctional functional antagonism between nitric oxide and ATP. The presence of NADPH-diaphorase- and quinacrine-positive neuronal cells and processes running to the muscle cells confirms a physiological role of nitric oxide and ATP in the ileal neurotransmission.

1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) inhibits cyclic GMP-PKG pathway-independent nonadrenergic, noncholinergic relaxation in longitudinal muscle of the rectum of Wistar-ST rats

Participation of the nitric oxide-cyclic GMP pathway in nonadrenergic, noncholinergic (NANC) relaxation induced by electrical field stimulation of longitudinal muscle of the rectum of Wistar-ST rats was studied by using a selective inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). ODQ concentration dependently inhibited the relaxation and at 10 microM, maximally inhibited it by 83%. However, results obtained with N(G)-nitro-L-arginine, L-arginine and exogenously added nitric oxide excluded the participation of nitric oxide in the relaxation. An inhibitor of cyclic GMP-dependent protein kinase (PKG) partially (39%) inhibited the relaxation. ODQ also significantly inhibited the relaxation, which persisted after the PKG inhibitor-treatment, by 85%. The results strongly suggest that ODQ inhibits the NANC relaxation in a cyclic GMP-PKG pathway-independent manner.

Differences in mediator of nonadrenergic, noncholinergic relaxation of the distal colon between Wistar-ST and Sprague-Dawley strains of rats

Participation of nitric oxide and vasoactive intestinal peptide (VIP) in electrical field stimulation-induced nonadrenergic, noncholinergic (NANC) relaxation of longitudinal muscle and in balloon distension-induced descending NANC relaxation of circular muscle were studied in the distal colon of Wistar-ST and Sprague-Dawley rats. The extent of the nitric oxide-mediated component was approximately 50% in longitudinal and circular muscle of Sprague-Dawley rats, whereas this component was absent in both muscles of Wistar-ST rats. The extent of the VIP-mediated component was approximately 40% in longitudinal muscle of Wistar-ST rats and circular muscle of Sprague-Dawley rats, whereas this component was absent in circular muscle of Wistar-ST rats and longitudinal muscle of Sprague-Dawley rats. In circular muscle of Sprague-Dawley rats, in which participation of both nitric oxide and VIP in the relaxation was suggested, inhibition of descending relaxation by N(G)-nitro-L-arginine (L-NOARG) together with VIP-(10-28) was similar to that by either of the antagonists, and exogenous VIP-induced relaxation was not affected by L-NOARG, but exogenous nitric oxide-induced relaxation was partly inhibited by VIP-(10-28). These results suggest a linkage of the pathways mediated by nitric oxide and VIP. In the immunohistochemical studies, nitric oxide synthase or VIP immunoreactive neurons were seen in the ganglia, primary internodal strands of the myenteric plexus and in the circular muscle layer. However, the overall appearance of immunoreactive cell bodies in the myenteric plexus and the numbers of immunoreactive fibers in the circular muscle layer appeared to be similar in Wistar-ST and Sprague-Dawley rats. These results suggest that mediators of NANC relaxation in the distal colon are different in different strains of rats, i.e., Wistar-ST and Sprague-Dawley, although no such difference was seen in immunohistochemical studies.

Involvement of cyclic AMP - PKA pathway in VIP-induced, charybdotoxin-sensitive relaxation of longitudinal muscle of the distal colon of Wistar-ST rats

The intracellular mechanism of vasoactive intestinal peptide (VIP)-induced, charybdotoxin (ChTx)-sensitive relaxation of longitudinal muscle of the distal colon of Wistar-ST rats was studied. A single pulse or 100 pulses at 10 Hz of electrical field stimulation (EFS) induced rapid transient relaxation or that with a subsequent contraction of the longitudinal muscle in the presence of atropine and guanethidine, respectively. Rp-8 bromo cAMPS, an inhibitor of cyclic AMP dependent protein kinase (PKA), at 30 microM inhibited the relaxations induced by EFS with a single or 100 pulses maximally by about 80 or 60%, respectively. It also inhibited VIP (300 nM)-induced relaxation by 82%. VIP (100 nM - 1 microM) increased the cyclic AMP content of longitudinal muscle myenteric plexus preparations obtained from the distal colon. ChTx at 100 nM almost completely inhibited 8 bromo cyclic AMP-induced relaxation of the distal segments. EFS with two or three pulses at 10 Hz induced inhibitory junction potentials consisting of two phases, rapid and subsequent slow hyperpolarization in the membrane potential of longitudinal smooth muscle cells. Rp-cAMPS, another inhibitor of PKA, inhibited the delayed slow hyperpolarization. It also inhibited the exogenously added VIP-induced hyperpolarization of the cell membrane. Thus, the present study suggests that activation of PKA via activation of VIP receptors is associated with activation of ChTx-sensitive K(+) channels in relaxation of longitudinal muscle of the distal colon of Wistar-ST rats. British Journal of Pharmacology (2000) 129, 140 - 146

Decrease in participation of nitric oxide in nonadrenergic, noncholinergic relaxation of rat intestine with age

Participation of nitric oxide in the electrical field stimulation-induced nonadrenergic, noncholinergic (NANC) relaxation in various intestinal regions was studied in 2- to 50-week-old Wistar rats. In the jejunum of 2-week-old rats, the extent of the nitric oxide-mediated component of the relaxation of longitudinal muscle was approximately 60-70%, whereas the component was 40-50% in 4-week-old rats and was absent in 8- and 50-week-old rats. Thus, nitric oxide seems to be the most important mediator at young ages but its significance is lost with age. The same tendency as that in the jejunum was also shown in longitudinal muscle of the ileum, proximal and distal colon, and rectum. The tendency was also shown in the circular muscle of the rectum. Sensitivity of the longitudinal muscle of the jejunum and proximal colon to exogenously added nitric oxide was high in younger rats. Immunoreactive structures for nitric oxide synthase were observed in the circular muscle layer of the rectum. The population of the structures was denser in 4-week-old than that in 50-week-old. The results suggest that NANC relaxation in every region of the intestine at 2-week-old is almost solely mediated by nitric oxide, and its significance as an inhibitory mediator gradually or rapidly decreases with age.

Nonadrenergic, noncholinergic relaxation mediated by nitric oxide with concomitant change in Ca2+ level in rectal circular muscle of rats

The mediators of nonadrenergic, noncholinergic (NANC) relaxation of the circular muscle of rat rectum were examined in vitro. In the circular muscle of rat rectum, NG-nitro-L-arginine (L-NOARG) at 10 microM did not affect electrical field stimulation-induced relaxation but at 100 microM it inhibited electrical field stimulation-induced relaxation by about 75% and 1-mM L-arginine reversed the inhibition. Exogenous nitric oxide (NO) (1-10 microM) concentration dependently relaxed the circular muscle. Electrical field stimulation increased the cyclic GMP content of the circular muscle to about twice its resting level. L-NOARG, even at 10 microM, completely inhibited the electrical field stimulation-induced elevation of cyclic GMP content. However, L-arginine at 1 mM did not reverse the inhibition in cyclic GMP content. Inhibitory junction potentials (i.j.ps) induced by electrical field stimulation in the circular muscle cells were not affected by L-NOARG, 100 microM. Apamin ( < or = microM) did not affect the electrical field stimulation-induced relaxation, but almost completely inhibited electrical field stimulation-induced i.j.ps. NO (0.3-10 microM) induced relaxation of the circular muscle with a concomitant decrease in intracellular Ca2+ level ([Ca2+]i). Abundant immunoreactivity of NO synthase was found in the circular muscle layer, in addition to myenteric and submucosal plexus. The results suggest that NO induces NANC relaxation with a concomitant change in [Ca2+]i in the circular muscle of rat rectum. However, the involvement of changes in cyclic GMP level and in membrane potentials in the mechanism was not shown in the present experimental conditions.