Longitudinal Muscle Strips Research Articles

Brain‐derived neurotrophic factor augments the contraction of intestinal longitudinal muscle strips induced by Carbachol

BackgroundWe have demonstrated that intestinal longitudinal smooth muscle cells synthesize and secrete brain derived neurotrophic factor (BDNF) in response to neuropeptide transmitters. But the function of this BDNF in the gastrointestinal tract is undetermined.Aimto test the effect of BDNF on agonist‐induced contraction in intestinal longitudinal smooth muscle.Material and methodRabbit longitudinal muscle strips were prepared from the intestine. The contraction of the muscle strips was recorded in response to substance P 10–6M (SP 10–6) and Carbachol 10–5M (CCh 10–5). Muscle strips were preincubated with 10 nM exogenous BDNF and the changes in SP/CCh‐induced contraction were examined. A Trk antagonist and two Trk B specific agonists were used to investigate the role of the Trk B receptor in the effect of BDNF on contraction.ResultsBDNF significantly enhanced the contraction of longitudinal smooth muscle induced by CCh 10–5. However, contraction induced by SP 10–6 was not affected by pretreatment with BDNF. The pan Trk receptor inhibitor (K252a) inhibited the effect of BDNF on CCh‐induced contraction. Moreover, two Trk B agonists (LM 22A4 & 7, 8‐dihydroxyflavone) augmented the CCh‐induced contraction of the longitudinal muscle strips.ConclusionBDNF enhances the cholinergic‐induced longitudinal muscle contraction through the activation of its cognate Trk B receptor.

Relaxant effect of chloroquine in rat ileum: possible involvement of nitric oxide and BKCa

Bitter perception has a particularly important role in host defence. However, to date, direct effects of bitter compounds on small intestinal motility have not been shown. This study investigated the effects of bitter compounds on the spontaneous contraction of longitudinal smooth muscle strips of rat ileum. Isolated longitudinal smooth muscle strips of rat ileum were used for tension recording in vitro. Immunofluorescence staining was used to identify the localization of TAS2R10 receptors. The spontaneous contraction of rat ileum was decreased after chloroquine administration. Other bitter compounds, such as quinine, denatonium and saccharin, exhibited similar effects. Chloroquine-induced relaxation was not blocked by tetrodotoxin, but was partially reversed by the nitric oxide synthase inhibitor L-NAME or the large conductance Ca(2+) -activated K(+) (BKCa) channel antagonist iberiotoxin. By surgically removing the small intestinal mucosa or bathing in Ca(2+) -free Krebs solution, the chloroquine-induced relaxation was largely attenuated. The immunofluorescence staining showed that TAS2R10 receptors were expressed in rat ileum. The results indicate that bitter receptor agonists induce relaxation of longitudinal smooth muscle strips of rat ileum, which is mediated by nitric oxide and BKCa channels.

Gut Microbial Products Regulate Murine Gastrointestinal Motility via Toll-Like Receptor 4 Signaling

Altered gastrointestinal motility is associated with significant morbidity and health care costs. Toll-like receptors (TLR) regulate intestinal homeostasis. We examined the roles of TLR4 signaling in survival of enteric neurons and gastrointestinal motility. We assessed changes in intestinal motility by assessing stool frequency, bead expulsion, and isometric muscle recordings of colonic longitudinal muscle strips from mice that do not express TLR4 (Tlr4(Lps-d) or TLR4(-/-)) or Myd88 (Myd88(-/-)), in wild-type germ-free mice or wild-type mice depleted of the microbiota, and in mice with neural crest-specific deletion of Myd88 (Wnt1Cre(+/-)/Myd88(fl/fl)). We studied the effects of the TLR4 agonist lipopolysaccharide (LPS) on survival of cultured, immortalized fetal enteric neurons and enteric neuronal cells isolated from wild-type and Tlr4(Lps-d) mice at embryonic day 13.5. There was a significant delay in gastrointestinal motility and reduced numbers of nitrergic neurons in TLR4(Lps-d), TLR4(-/-), and Myd88(-/-) mice compared with wild-type mice. A similar phenotype was observed in germ-free mice, mice depleted of intestinal microbiota, and Wnt1Cre(+/-)/Myd88(fl/fl) mice. Incubation of enteric neuronal cells with LPS led to activation of the transcription factor nuclear factor (NF)-κB and increased cell survival. Interactions between enteric neurons and microbes increases neuron survival and gastrointestinal motility in mice. LPS activation of TLR4 and NF-κB appears to promote survival of enteric neurons. Factors that regulate TLR4 signaling in neurons might be developed to alter gastrointestinal motility.

Myogenic regional responsiveness to cholinergic and vipergic stimulation in human colon

Differences in the actions of enteric neurotransmitters on colonic circular and longitudinal muscle layers have not been clearly determined, nor the possible existence of intrinsic myogenic phenotypes that might contribute to regional differences in human colon motor activity. The aim of this study was to analyze the direct pharmaco-mechanical coupling of carbachol (CCh) and vasoactive intestinal polypeptide (VIP) on human colonic smooth muscle strips and cells. Circular and longitudinal muscle strips and cells were obtained from 15 human specimens of ascending and sigmoid colon. Both isometric tension on muscle strips and contraction and relaxation on cells were measured in response to increasing CCh and VIP concentrations. Circular muscle strips of ascending colon were more sensitive to the effect of CCh than that of sigmoid colon, EC(50) values being, respectively, 4.15μmolL(-1) and 8.47μmolL(-1) (P<0.05), although there were no differences in maximal responses. No regional differences were observed in longitudinal muscle strips or in smooth muscle cells. Maximal responses to CCh were higher on circular than longitudinal muscle strips and cells throughout the colon. A greater sensitivity to VIP was observed in ascending colon compared with sigmoid colon, both in circular (EC(50:) 0.041 and 0.15μmolL(-1) , respectively, P<0.01) and longitudinal (EC(50:) 0.043 and 0.09μmolL(-1) , respectively, P<0.05) strips, and similar differences were observed in longitudinal smooth muscle cells (EC(50:) 44.85 and 75.24nmolL(-1) , respectively, P<0.05). Regional myogenic differences in pharmaco-mechanical coupling between the enteric neurotransmitters and smooth muscle contribute to the complex regional motor patterns of human colon.

Origin of Motion in the Human Ureter: Mechanics, Energetics and Kinetics of the Myosin Molecular Motors

Ureteral peristalsis is the result of coordinated mechanical motor performance of longitudinal and circular smooth muscle layer of the ureter wall. The main aim of this study was to characterize in smooth muscle of proximal segments of human ureter, the mechanical properties at level of muscle tissue and at level of myosin molecular motors. Ureteral samples were collected from 15 patients, who underwent nephrectomy for renal cancer. Smooth muscle strips longitudinally and circularly oriented from proximal segments of human ureter were used for the in vitro experiments. Mechanical indices including the maximum unloaded shortening velocity (Vmax), and the maximum isometric tension (P0) normalized per cross-sectional area, were determined in vitro determined in electrically evoked contractions of longitudinal and circular smooth muscle strips. Myosin cross-bridge (CB) number per mm2 (Ψ) the elementary force per single CB (Ψ) and kinetic parameters were calculated in muscle strips, using Huxley's equations adapted to nonsarcomeric muscles. Longitudinal smooth muscle strips exhibited a significantly (p<0.05) faster Vmax (63%) and a higher P0 (40%), if compared to circular strips. Moreover, longitudinal muscle strips showed a significantly higher unitary force (Ψ) per CB. However, no significant differences were observed in CB number, the attachment (f1) and the detachment (g2) rate constants between longitudinal and circular muscle strips. The main result obtained in the present work documents that the mechanical, energetic and unitary forces per CB of longitudinal layer of proximal ureter are better compared to the circular one; these preliminary findings suggested, unlike intestinal smooth muscle, a major role of longitudinal smooth muscle layer in the ureter peristalsis.

Activity in varicosities within the myenteric plexus between and during the colonic migrating motor complex in the isolated murine large intestine.

Neuronal communication within the myenteric plexus occurs when action potentials along nerve fibers produce Ca(2+) transients in varicosities leading to exocytosis of vesicles and neurotransmitters release. We used Ca(2+) transients in varicosities to monitor action potential activity in myenteric nerve pathways both between and during the colonic migrating motor complex (CMMC) in the isolated murine colon. Strips of longitudinal muscle were removed to reveal the myenteric ganglia, which were then loaded with Fluo-4. Many varicosities, including synaptotagmin 1 labeled varicosities, exhibited ongoing Ca(2+) transients (duration of unitary Ca(2+) transient 3.9 s). Between CMMCs, varicosities fired at a frequency of 0.6 Hz, which correlated with spontaneous inhibitory junction potentials in the circular muscle, suggesting they were mainly in inhibitory nerve pathways. During a CMMC other previously quiescent varicosities fired at 1.3 Hz (max. 2.0 Hz) for the duration (24 s) of the CMMC, suggesting they were on excitatory nerve pathways. Activity in varicosities was correlated with Ca(2+) transient responses in a number of neurons. Some varicosities appeared to release an inhibitory neurotransmitter that reduced activity in nNOS-positive neurons. Varicosities along the same nerve fiber exhibited identical patterns of activity that allowed nerve fibers to be traced throughout the myenteric plexus and internodal strands. Activity in varicosities was reduced by hexamethonium (100 μmol L(-1) ), and blocked by ω-conotoxin GVIA (200 nM) and tetrodotoxin (1 μmol L(-1) ; TTX). Ca(2+) imaging of varicosities allows for a determination of activity in neural pathways within the enteric nervous system.

Ca2+ transients in myenteric glial cells during the colonic migrating motor complex in the isolated murine large intestine

Enteric glia cells (EGCs) form a dense network around myenteric neurons in a ganglia and are likely to have not only a supportive role but may also regulate or be regulated by neural activity. Our aims were to determine if EGCs are activated during the colonic migrating motor complex (CMMC) in the isolated murine colon. Strips of longitudinal muscle were removed and Ca(2+) imaging (Fluo-4) used to study activity in EGCs within myenteric ganglia during CMMCs, followed by post hoc S100 staining to reveal EGCs. The cell bodies of EGCs and their processes formed caps and halos, respectively, around some neighbouring myenteric neurons. Some EGCs (36%), which were largely quiescent between CMMCs, exhibited prolonged tetrodotoxin (TTX; 1 μm)-sensitive Ca(2+) transients that peaked ∼39 s following a mucosal stimulus that generated the CMMC, and often outlasted the CMMC (duration ∼23 s). Ca(2+) transients in EGCs often varied in duration within a ganglion; however, the duration of these transients was closely matched by activity in closely apposed nerve varicosities, suggesting EGCs were not only innervated but the effective innervation was localized. Furthermore, all EGCs, even those that were quiescent, responded with robust Ca(2+) transients to KCl, caffeine, nicotine, substance P and GR 64349 (an NK2 agonist), suggesting they were adequately loaded with indicator and that some EGCs may be inhibited by substances released by neighbouring neurons. Intracellular Ca(2+) waves were visualised propagating between closely apposed glia and from glial cell processes to the soma (velocity 12 μm s(-1)) where they produced an accumulative rise in Ca(2+), suggesting that the soma acts as an integrator of Ca(2+) activity. In conclusion, Ca(2+) transients in EGCs occur secondary to nerve activity; their activation is driven by intrinsic excitatory nerve pathways that generate the CMMC.

Contribution of phospholipase C and protein kinase C but not endothelin-converting enzyme to contractile responses of ethanol

Aim: To evaluate the possible roles of phospholipase C, protein kinase C, and endothelin-converting enzyme on contractions induced by ethanol (164 mM) in isolated gastric fundal strips of mice. Materials and methods: After the mice were killed, the stomach of each was removed and longitudinal muscle strips were prepared from the gastric fundus. The strips were mounted in organ baths and their responses were recorded isometrically. Ethanol (164 mM) was added to the organ baths and a steady-state contraction was obtained. After the first ethanol response was recorded, the preparations were incubated separately with lidocaine (1-100 µM), neomycin (10-500 µM), safingol (0.5-5 µM), and SM-19712 (1-50 µM) for 40 min. The second ethanol response was then examined in the presence of the drug used in the incubation period. Results: Lidocaine (1-100 µM), a local anesthetic agent, did not modulate the contractions induced by ethanol in isolated gastric fundal strips of mice. In contrast, neomycin (10-500 µM), a selective inhibitor of phospholipase C, and safingol (0.5-5 µM), a selective inhibitor of protein kinase C, decreased the ethanol-induced contractions. SM-19712 (1-50 µM), a selective inhibitor of endothelin-converting enzyme, failed to affect these contractions. Conclusion: The contractile effect of ethanol may be muscular rather than neuronal in the gastric fundal strips of mice. In addition, phospholipase C and protein kinase C pathways may have a role in contractions due to ethanol in the mouse gastric fundus. On the other hand, endothelin-converting enzyme may not have a regulatory role in the contractile responses of ethanol in the same tissue.

Mechanisms of Motility Change on Trinitrobenzenesulfonic Acid-Induced Colonic Inflammation in Mice

Ulcerative colitis is an inflammatory bowel disease (IBD) characterized by recurrent episodes of colonic inflammation and tissue degeneration in human or animal models. The contractile force generated by the smooth muscle is significantly attenuated, resulting in altered motility leading to diarrhea or constipation in IBD. The aim of this study is to clarify the altered contractility of circular and longitudinal smooth muscle layers in proximal colon of trinitrobenzen sulfonic acid (TNBS)-induced colitis mouse. Colitis was induced by direct injection of TNBS (120 mg/kg, 50% ethanol) in proximal colon of ICR mouse using a 30 G needle anesthetized with ketamin (50 mg/kg), whereas animals in the control group were injected of 50% ethanol alone. In TNBS-induced colitis, the wall of the proximal colon is diffusely thickened with loss of haustration, and showed mucosal and mucular edema with inflammatory infiltration. The colonic inflammation is significantly induced the reduction of colonic contractile activity including spontaneous contractile activity, depolarization-induced contractility, and muscarinic acetylcholine receptor-mediated contractile response in circular muscle layer compared to the longitudinal muscle layer. The inward rectification of currents, especially, important to Ca2+ and Na+ influx-induced depolarization and contraction, was markedly reduced in the TNBS-induced colitis compared to the control. The muscarinic acetylcholine-mediated contractile responses were significantly attenuated in the circular and longitudinal smooth muscle strips induced by the reduction of membrane expression of canonical transient receptor potential (TRPC) channel isoforms from the proximal colon of the TNBS-induced colitis mouse than the control.

Role of tachykinin and neurokinin receptors in the regulation of ovine omasal contractions

The present study investigated a role of tachykinins (TK) and neurokinin (NK) receptors (NK-R) in the non-cholinergic regulation of omasal contractions in sheep. Semiquantitative reverse transcription (RT)-PCR revealed that both preprotachykinin (PPT)-A and PPT-B mRNA were distributed in the omasal muscle layers and that NK-R type-1 (NK-1R) and type-2 (NK-2R) mRNA were largely expressed in the same tissues. Cumulative application of substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) at 0.03–10μM induced tonic contractions of omasal muscle strips, and the contractile amplitude increased in order of NKB<SP≪NKA in longitudinal and circular muscle strips. Although cumulative application of NK-1R antagonist, L-732,138, at 1–100μM did not significantly inhibit SP- and NKA-induced contractions in both muscle layers, NK-2R antagonist GR159897 at 30–100μM significantly inhibited NKA-induced contraction of longitudinal muscles and showed tendency to inhibit that in circular muscles. Electric field stimulation (EFS)-induced contractions of omasal muscle strips, which were atropine-resistant, were significantly inhibited by GR159897 at 30 and 100μM in both muscle strips, and L-732,138 at 30 and 100μM in longitudinal muscles, though the inhibition in the latter was very weak. The results of the present study suggest that, though all mRNA coding TKs and NK-R subtypes were expressed in omasal muscle layer, NK-2R in both muscle layers and, to much lesser extent, NK-1R in longitudinal muscles are involved in the regulation of omasal contraction, and that NKA is presumably a primary non-cholinergic excitatory neurotransmitter released from motor neurons in the ovine omasum.

Exogenous oxytocin reverses the decrease of colonic smooth muscle contraction in antenatal maternal hypoxia mice via ganglia

Oxytocin (OT) has been reported to have a potential protective effect on stress-induced functional gastrointestinal disorders. This study determined whether colonic contraction in adults was affected by antenatal maternal hypoxia, and whether OT is involved in antenatal maternal hypoxia induced colonic contraction disorder. Isometric spontaneous contractions were recorded in colonic longitudinal muscle strips in order to investigate colonic contractions and the effects of exogenous OT on the contraction in antenatal maternal hypoxia and control mice. Both high potassium and carbachol-induced contractions of proximal colon but not distal colon were reduced in antenatal maternal hypoxia mice. Exogenous OT decreased the contractions of proximal colonic smooth muscle strips in control mice, while it increased contractions in antenatal maternal hypoxia mice. OT increased the contractions of distal colonic smooth muscle strips in both antenatal maternal hypoxia and control mice. Hexamethonium blocked the OT-induced potentiation of proximal colon but not distal colon in antenatal maternal hypoxia mice. These results suggest that exogenous oxytocin reverses the decrease of proximal colonic smooth muscle contraction in antenatal maternal hypoxia mice via ganglia.

Effects of muscarinic receptor antagonists on acetylcholine‐induced contractions of jejunal smooth muscle in horses

This study investigated the effects of a muscarinic type 1 (M(1)), 2 (M(2)), and 3 (M(3)) antagonists (4-DAMP, pirenzepine, and methoctramine, respectively) on acetylcholine (Ach)-induced contractions of longitudinal jejunal muscle strips of horses. Strips were irrigated with Krebs-Henseleit solution gassed with 95% O(2) and 5% CO(2), and the developed tension in response to Ach was recorded before and after incubation with increasing concentrations of 4-DAMP (10(-8)-10(-6) M), pirenzepine (10(-6)-10(-4) M), and methoctramine (10(-5)-10(-3) M). When competitive antagonism was characterized, the affinity constant (pA(2)) was calculated by Schild plots. A parallel rightward shift in the concentration-response curves was observed after 4-DAMP and pirenzepine. Methoctramine presented a dual effect on the concentration-response curves: lower concentrations induced a parallel rightward shift without altering the maximum intensity of contraction (E(max)), while the highest concentration increased slope of the concentration-response curve and increased E(max). The pA(2) for 4-DAMP and pirenzepine was 9.18 and 7.13, respectively. Acetylcholine-induced contractions of longitudinal jejunal smooth muscle are mediated mainly via M(3) receptors. The complex role of M(2) receptors in jejunal smooth muscle contractions was evident because methoctramine potentiated the contractile response to higher doses of Ach.

K V7 channels regulate muscle tone and nonadrenergic noncholinergic relaxation of the rat gastric fundus

Voltage-dependent type 7 K + (K V7) channels play important physiological roles in neurons and muscle cells. The aims of the present study were to investigate the motor effects of K V7 channel modulators in the rat gastric fundus and the expression of K V7 channels in this tissue. Muscle tone and electrical field stimulation (EFS)-evoked relaxations of precontracted longitudinal muscle strips of the rat gastric fundus were investigated under nonadrenergic noncholinergic conditions by organ bath studies. Gene expression was studied by real-time PCR and tissue localization of channels was investigated by immunohistochemistry. The K V7 channel blocker XE-991 induced concentration-dependent contractions, with mean pD 2 and E max of 5.4 and 48% of the maximal U46619-induced contraction, respectively. The K V7 channel activators retigabine and flupirtine concentration-dependently relaxed U46619-precontracted strips, with pD 2s of 4.7 and 4.4 and E max of 93% and 91% of the maximal relaxation induced by papaverine, respectively. XE-991 concentration-dependently inhibited retigabine-induced relaxation with a pIC 50 of 6.2. XE-991 and DMP-543, another K V7 channel blocker, increased by 13–25% or reduced by 11–21% the relaxations evoked by low- or high-frequency EFS, respectively. XE-991 also reduced the relaxation induced by vasoactive intestinal polypeptide (VIP) by 33% of controls. Transcripts encoded by all K V7 genes were detected in the fundus, with 7.4 and 7.5 showing the highest expression levels. K V7.4 and 7.5 channels were visualized by confocal immunofluorescence in both circular and longitudinal muscle layers. In conclusion, in the rat proximal stomach, K V7 channels appear to contribute to the resting muscle tone and to VIP- and high-frequency EFS-induced relaxation. K V7 channel activators could be useful relaxant agents of the gastric smooth muscle.

Hydrogen Sulfide Modulates Contractile Function in Rat Jejunum

Effects of hydrogen sulfide (H(2)S), a third gasotransmitter of the gut, are not well understood. The aim of this study was to determine effects/mechanisms of H(2)S action on contractile function in rat jejunal muscle. Transmural strips of longitudinal muscle were evaluated. Response to sodium hydrosulfide (NaHS, H(2)S donor; 10(-5)-10(-3)M) was studied on spontaneous contractile activity and after precontraction (bethanechol, 3 × 10(-6)M). Atropine, propranolol, phentolamine, tetrodotoxin, capsaicin, L-N(G)-nitro arginine (L-NNA), and glibenclamide were used to determine mechanisms. L-cysteine (10(-4)-10(-2)M; substrate for H(2)S production) and aminooxyacetic acid and DL-propargylglycine (inhibitors of enzymes generating H(2)S endogenously) were used to study endogenous production. Aminooxyacetic acid, DL-propargylglycine, L-NNA, and vasoactive intestinal polypeptide (VIP) antagonist [D-p-Cl-Phe(6),Leu(17)]-VIP were used to study H(2)S release during electrical field stimulation (EFS) and interaction with VIP and nitric oxide. Immunohistofluorescence of jejunal whole mounts was performed for endogenous H(2)S-producing enzymes. Cystathionine-β-synthase and cystathionine-γ-lyase were expressed only in myenteric plexus. NaHS suppressed spontaneous and stimulated contractile activity (P < 0.01). Glibenclamide prevented some suppression by NaHS (P = 0.01) of stimulated contractile activity but did not prevent suppression of spontaneous contractile activity. Other drugs had no effect on spontaneous contractile activity but increased inhibitory effects of NaHS on spontaneous and stimulated contractile activity (P < 0.05). L-cysteine had no effects on contractile activity. Inhibitors altered basal and stimulated activity suggesting endogenous release ofH(2)S. H(2)S presumably suppresses contractile activity in jejunum by direct effects on smooth muscle. Mechanism(s) of inhibition remains unclear, because blocking known neurotransmitters enhanced H(2)S-induced suppression, while blocking adenosine triphosphate (ATP)-sensitive K(+)-channels did not block H(2)S-induced inhibition.

Changes in muscarinic ligand binding to intestinal muscle strips produced by pre-exposure to hypotonic conditions.

The extent of the binding of [3H]propylbenzilylcholine mustard (3H-PrBCM) to muscarinic receptors in longitudinal muscle strips from guinea-pig small intestine is increased by nearly 50% when the strips are preexposed to distilled water before measurement of 3H-PrBCM binding in Krebs-Henseleit solution. The apparent rate constant for 3H-PrBCM-receptor complex formation is more than double that of intact strips. The curves for the inhibition of 3H-PrBCM binding by methylatropinium bromide in normal and treated strips are superimposable, but, in contrast, distilled water pretreatment shifts the inhibition curve for carbachol to lower concentrations by a factor of 5-6. The inhibition curve for methylfurmethide is also shifted, by a factor of approximately 4, but the effect on the curve for hexyltrimethylammonium (C6TMA) is slight. The relative inhibition produced by benzhexol in the two preparations was variable. Comparison of the rate of equilibration of benzhexol with muscarinic receptors in intact and in distilled water pretreated muscle indicates that this inconsistency is unlikely to be due to incomplete equilibration.

The effects of various peptides on human isolated gut muscle.

The effects of eleven peptides of gastrointestinal origin have been studied on the contraction, relaxation and spontaneous activity of circular and longitudinal muscle strips from different regions of the human gastrointestinal tract. The effects varied with the peptides and sometimes with the region and muscle layer. There was either contraction, no effect, or relaxation and/or inhibition of an acetylcholine-induced contraction. Responses to some peptides are consistent with the possibility that they may contribute directly to the control of motility: galanin, neurotensin and substance P might be involved in contraction, and vasoactive intestinal peptide, peptide histidine isoleucine and peptide histidine methionine might be inhibitory transmitters.

The effects of eserine and neostigmine on the guinea-pig ileum and on ileal longitudinal muscle strips.

Abstract Eserine and neostigmine produced spasms of the guinea-pig isolated ileum that were concentration-related (4 ng-16 μg/ml). Hexamethonium (100 μg/ml) and tetrodotoxin (100 ng/ml) reduced the spasmogenic activity of both drugs. Neostigmine, but not eserine, overcame the hexamethonium antagonism. Pretreatment of the ileum with dyflos (1 μg/ml for 10 min) did not affect the action of either eserine or neostigmine, therefore the spasm was not due to inhibition of cholinesterase. The residual response to eserine or neostigmine after tetrodotoxin was abolished by hyoscine (4 ng/ml). Isolated longitudinal muscle strips were so prepared to be innervated or denervated. Both types of strip gave similar bradykinin maxima but the response of the denervated strip to eserine and neostigmine was reduced to 40% of the innervated strip and the remaining response was blocked by hyoscine (2 ng/ml). It is concluded that eserine and neostigmine have an indirect action on the smooth muscle of the ileum that is the result of acetylcholine release from cholinergic nerves. Inhibition of cholinesterase would not seem to be important for this action. A second component of the action of these two drugs appears to be a direct effect on the muscarinic receptors of the smooth muscle.

A preliminary investigation of the pharmacology of longitudinal muscle strips from human isolated jejunum.

Abstract The effects of drugs on longitudinal muscle strips of human jejunum were studied in vitro. The muscarinic site of action of acetylcholine was demonstrated. The sympathomimetic amines phenylephrine, noradrenaline and isoprenaline each produced only a relaxation by an action on adrenergic α- and β-receptors. The presence of both types of receptor was demonstrated by selective adrenergic blockade with pronethalol or Hydergine. The ganglion stimulating agent dimethylphenyl-piperazinium produced a contraction by an action on intramural cholinergic nervous tissue. When the contractile response was blocked by hyoscine, a relaxation occurred, due to the stimulation of an adrenergic mechanism which could be either the sympathetic nerves of the intrinsic nerve plexus or adrenergic stores in the bowel wall. The contraction produced by histamine was not inhibited by hyoscine or hexamethonium but was blocked by mepyramine, thus indicating a direct effect of the drug on the smooth muscle. 5-Hydroxytryptamine produced a contraction by a direct action on the muscle, since the response was not inhibited by hyoscine or hexamethonium but was blocked by methysergide (UML 491).

The spontaneous electrical and mechanical activity of the longitudinal smooth muscle of the rabbit duodenum and its modification by drugs and temperature changes.

Abstract The electrical and mechanical activity of strips of longitudinal smooth muscle from the rabbit duodenum was recorded using the sucrose gap method. The muscle exhibited rhythmic tension changes each of which was associated with a slow potential wave of electric depolarization surmounted by a burst of spike activity (a multispike complex). Cooling the tissue reduced the frequency of tension waves and multispike complexes. Catecholamines produced a reduction in the amplitude of tension waves. This was associated with hyperpolarization and decreased spike activity. Slow wave frequency and amplitude were unaffected. Acetylcholine, methacholine and histamine produced tension wave fusion associated with depolarization and increased spike activity.

The inhibitory effect of dopamine on cat gastric smooth muscle.

The inhibitory effect of dopamine has been studied in longitudinal and circular muscle strips of the cat gastric fundus. When tone was raised by transmural electrical stimulation and by administration of methacholine, dopamine concentration-dependently relaxed the strips but the inhibitory effect of dopamine was clearly more pronounced on electrically-induced tone. The effect of dopamine was not influenced by the presence of cocaine or hydrocortisone. The relaxant effect of dopamine, when tone was raised by methacholine, was not influenced by alpha- and dopamine receptor antagonists but it was significantly reduced by propranolol and ICI 118551 (erythro-DL-1-(7-methylindan-4-yloxy)-3- isopropylaminobutan-2-ol). The inhibitory effect of dopamine on the electrically-induced tone was significantly reduced by phentolamine; domperidone tended to reduce the effect of the lower concentrations of dopamine. In the presence of propranolol, phentolamine and rauwolscine concentration-dependently antagonized the inhibitory effect of dopamine on electrically-induced tone, while prazosin was without influence. These results indicate that the inhibitory effect of dopamine in the cat gastric fundus is mainly due to interaction with postjunctional beta 2-adrenoceptors on the smooth muscle cells and with prejunctional alpha 2-adrenoceptors on the intramural cholinergic neurons.