Amplitude Of Twitch Contractions Research Articles

Mechanisms of dysfunction in patient-derived cardiomyocytes with the hypertrophic cardiomyopathy-myosin binding protein-C e258K mutation

Mutations in cardiac myosin binding protein-C (cMyBP-C) are the most common cause of hypertrophic cardiomyopathy (HCM). We recently described the highly penetrant MYBPC3-c.772G>A (p.E258K) mutation with founder effect in Tuscany, Italy. Isolated myofibrils from patient myectomies indicated accelerated cross-bridge kinetics and higher energy cost of tension. Concurrently, prolonged action potentials and calcium transient duration preserves twitch contraction amplitude and duration in intact cells and trabeculae (Pioner et al., Biophys J, 2020;118:35a).

ATP-dependent potassium channels contribute to motor regulation of esophageal striated muscle in rats

The aim of the present study was to clarify roles of ATP-dependent potassium channels (KATP channels) in motility of the striated muscle portion in the esophagus. An isolated segment of the rat esophagus was placed in an organ bath and mechanical responses were recorded using a force transducer. Electrical stimulation of the vagus nerve evoked contractile response of striated muscle in the esophageal segment. Application of glibenclamide, an antagonist of KATP channels, increased amplitude of vagally mediated twitch contractions of the rat esophagus. On the other hand, minoxidil, an agonist of KATP channels, decreased amplitude of twitch contractions. RT-PCR revealed the expression of subunits of KATP channels in esophageal tissue. In addition, immunopositivity for subunits of KATP channels was observed in the striated muscle cells of the esophageal muscle layer. These findings indicate that KATP channels contribute to motor regulation of striated muscle in the rat esophagus.

Knockdown of col22a1 gene in zebrafish induces a muscular dystrophy by disruption of the myotendinous junction

The myotendinous junction (MTJ) is the major site of force transfer in skeletal muscle, and defects in its structure correlate with a subset of muscular dystrophies. Col22a1 encodes the MTJ component collagen XXII, the function of which remains unknown. Here, we have cloned and characterized the zebrafish col22a1 gene and conducted morpholino-based loss-of-function studies in developing embryos. We showed that col22a1 transcripts localize at muscle ends when the MTJ forms and that COLXXII protein integrates the junctional extracellular matrix. Knockdown of COLXXII expression resulted in muscular dystrophy-like phenotype, including swimming impairment, curvature of embryo trunk/tail, strong reduction of twitch-contraction amplitude and contraction-induced muscle fiber detachment, and provoked significant activation of the survival factor Akt. Electron microscopy and immunofluorescence studies revealed that absence of COLXXII caused a strong reduction of MTJ folds and defects in myoseptal structure. These defects resulted in reduced contractile force and susceptibility of junctional extracellular matrix to rupture when subjected to repeated mechanical stress. Co-injection of sub-phenotypic doses of morpholinos against col22a1 and genes of the major muscle linkage systems showed a synergistic gene interaction between col22a1 and itga7 (α7β1 integrin) that was not observed with dag1 (dystroglycan). Finally, pertinent to a conserved role in humans, the dystrophic phenotype was rescued by microinjection of recombinant human COLXXII. Our findings indicate that COLXXII contributes to the stabilization of myotendinous junctions and strengthens skeletal muscle attachments during contractile activity.

Pharmacological effects of Eugenia punicifolia (Myrtaceae) in cholinergic nicotinic neurotransmission

The effects of the aqueous crude extract (5%) of Eugenia punicifolia on cholinergic nicotinic neurotransmission were investigated. Actions of aqueous crude extract over the inhibitory effect of the cholinergic nicotinic antagonists gallamine or pancuronium, on contractions induced by electrical stimulation of phrenic nerve of rat diaphragm, were studied. Tissues were mounted as for isotonic contractions and stimulation was delivered at submaximal voltage. Addition of Eugenia punicifolia did not alter the amplitude of twitch contraction. Gallamine (IC 50: 28.8 ± 0.51 μM) or pancuronium (IC 50: 3.16 ± 0.11 μM) completely inhibited twitch contractions. After the maximum effect of the antagonists was achieved, addition of the aqueous crude extract (0.5–1.0 mL) totally recovered the responses to electrical stimulation. Neostigmine, a reversible acethylcholinesterase inhibitor, partially recovered responses (49.70 ± 6.90% at 1 μM). In another series of experiments, previous incubation of the extract (0.5 mL) shifted to the right inhibitory concentration–response curves for the antagonists gallamine (IC 50 before E. punicifolia: 35.8 ± 1.61 μM; IC 50, after E. punicifolia: 2.24 ± 0.04 mM) and pancuronium (IC 50, before E. punicifolia: 3.55 ± 0.13 μM; IC 50, after E. punicifolia: 0.39 ± 0.01 mM). Our results show that the aqueous extract of E. punicifolia recovered the action of competitive nicotinic antagonists at the neuromuscular junction. A receptor-mediated mechanism or the possibilities of interactions of the extract with the enzyme acethylcholinesterase, however, remain to be investigated.

Increased Sarcoplasmic Reticulum Calcium Leak but Unaltered Contractility by Acute CaMKII Overexpression in Isolated Rabbit Cardiac Myocytes

The predominant cardiac Ca2+/calmodulin-dependent protein kinase (CaMK) is CaMKIIdelta. Here we acutely overexpress CaMKIIdeltaC using adenovirus-mediated gene transfer in adult rabbit ventricular myocytes. This circumvents confounding adaptive effects in CaMKIIdeltaC transgenic mice. CaMKIIdeltaC protein expression and activation state (autophosphorylation) were increased 5- to 6-fold. Basal twitch contraction amplitude and kinetics (1 Hz) were not changed in CaMKIIdeltaC versus LacZ expressing myocytes. However, the contraction-frequency relationship was more negative, frequency-dependent acceleration of relaxation was enhanced (tau(0.5Hz)/tau(3Hz)=2.14+/-0.10 versus 1.87+/-0.10), and peak Ca2+ current (ICa) was increased by 31% (-7.1+/-0.5 versus -5.4+/-0.5 pA/pF, P<0.05). Ca2+ transient amplitude was not significantly reduced (-27%, P=0.22), despite dramatically reduced sarcoplasmic reticulum (SR) Ca2+ content (41%; P<0.05). Thus fractional SR Ca2+ release was increased by 60% (P<0.05). Diastolic SR Ca2+ leak assessed by Ca2+ spark frequency (normalized to SR Ca2+ load) was increased by 88% in CaMKIIdeltaC versus LacZ myocytes (P<0.05; in an multiplicity-of-infection-dependent manner), an effect blocked by CaMKII inhibitors KN-93 and autocamtide-2-related inhibitory peptide. This enhanced SR Ca2+ leak may explain reduced SR Ca2+ content, despite measured levels of SR Ca2+-ATPase and Na+/Ca2+ exchange expression and function being unaltered. Ryanodine receptor (RyR) phosphorylation in CaMKIIdeltaC myocytes was increased at both Ser2809 and Ser2815, but FKBP12.6 coimmunoprecipitation with RyR was unaltered. This shows for the first time that acute CaMKIIdeltaC overexpression alters RyR function, leading to enhanced SR Ca2+ leak and reduced SR Ca2+ content but without reducing twitch contraction and Ca2+ transients. We conclude that this is attributable to concomitant enhancement of fractional SR Ca2+ release in CaMKIIdeltaC myocytes (ie, CaMKII-dependent enhancement of RyR Ca2+ sensitivity during diastole and systole) and increased ICa.

Participation of endogenous nitric oxide in the effect of hypoxia in vitro on neuro-effector transmission in guinea-pig ileum

The implication of endogenous nitric oxide in the effect of hypoxia on the neurotransmission in the enteric nervous system of guinea-pig ileum was studied in vitro. Three methodological approaches have been used: (i) Stretch-induced phases of peristaltic reflex in ileal segments; (ii) twitch contractions of longitudinal segments, evoked by electrical field stimulation; and (iii) release of [ 3H]acetylcholine from longitudinal muscle-myenteric plexus preparations, measured by liquid spectrophotometry. The effect of nitric oxide synthase inhibitor N ω-nitro-L-arginine (L-NNA, 100 μM) was studied under normoxic conditions. L-NNA did not change significantly the ascending contraction phase of peristaltic reflex and the amplitude of twitch contractions. However, the same concentration of L-NNA increased the stimulation-evoked acetylcholine release. The descending relaxation phase decreased in the presence of L-NNA. In another set of experiments, hypoxia was mimicked by replacement of oxygen from the perfusion medium with nitrogen for a period of 30 min. Hypoxia significantly decreased the ascending contraction phase, the twitch contractions, and the release of acetylcholine from the myenteric plexus. Under hypoxic conditions, pretreatment with L-NNA did not change either the contractile responses, nor the release of acetylcholine. Our results suggest that under conditions of oxygen deprivation, endogenous nitric oxide seems to be inefficient in modulating the cholinergic neurotransmission in guinea-pig ileum.

Nitric oxide inhibits smooth muscle responses evoked by cholinergic nerve stimulation in the guinea pig gastric fundus.

In circular smooth muscle tissues of the guinea pig gastric fundus, transmural nerve stimulation (TNS) evoked an atropine-sensitive cholinergic excitatory junction potential (e.j.p.) and, after inhibiting the e.j.p. with atropine, an apamin-sensitive nonadrenergic noncholinergic (NANC) inhibitory junction potential (i.j.p.). The amplitude of e.j.p.s was similar when the frequency of TNS was low (<0.5 Hz), but it decreased successively (depression phenomenon) when the frequency was high (>1 Hz). The depression phenomenon was attenuated after inhibiting the production of nitric oxide (NO) with N(omega)-nitro-L-arginine (NOLA), but was not altered by inhibiting the i.j.p. with apamin. The e.j.p.s were increased in amplitude by the inhibition of cholinesterase activity, but they were decreased by NO produced from SNP with no alteration of their depression phenomenon. Isometric twitch contractions were depressed during high-frequency TNS. NOLA caused an increase in the amplitude of twitch contractions and the attenuation of their depression that changed the transient contraction produced by high-frequency TNS (1 Hz) to a tetanic one. SNP reduced the amplitude of twitch contractions, with no alteration of the depression phenomena. Contractions produced by low concentrations of acetylcholine, but not by high concentrations, were attenuated by SNP, with no alteration of the membrane depolarization. The results suggest that NO produced during TNS has inhibitory actions on cholinergic transmission; the depression of e.j.p.s is mainly prejunctional events, and the depression of mechanical responses is mainly postjunctional events.

Inhibitory Actions of Indomethacin on Electrical and Mechanical Responses Produced by Nerve Stimulation in Circular Smooth Muscle of the Guinea-Pig Gastric Fundus

The effects of indomethacin on electrical and mechanical responses produced by transmural nerve stimulation (TNS) were investigated in isolated circular smooth muscle of the guinea-pig gastric fundus. TNS evoked a cholinergic excitatory junction potential (e.j.p.). The e.j.p.s were inhibited by 1-10 microM indomethacin, in a concentration-dependent manner, with no marked alteration of the resting membrane potential. Exogenously applied acetylcholine caused a depolarization of the membrane that was not altered by indomethacin. TNS evoked a cholinergic twitch contraction at low frequencies (0.1 Hz). A train of TNS's at high frequency (1 Hz) produced a transient contraction with a subsequent sustained relaxation. Indomethacin reduced the resting tension and inhibited these TNS-induced contractions. Application of Nomega-nitro-L-arginine (NOLA), an inhibitor of nitric oxide (NO) synthesis, increased the amplitude of twitch contractions, and altered transient contractions to tetanic contractions during TNS at a frequency of 1 Hz, also with an increased amplitude. In the presence of NOLA, indomethacin (5 microM) again reduced the resting tension and inhibited TNS-induced contractions. This inhibition was greater for twitch contractions than for tetanic contractions. Nifedipine reduced the TNS-induced contractions, while addition of indomethacin further reduced the amplitude of contractions. Contractions produced by low concentrations of acetylcholine (0.1 microM) were inhibited by indomethacin, while those produced by 1 microM were not. These results indicate that the inhibitory actions of indomethacin on TNS-induced contractions do not involve enhanced production of NO or selective inhibition of voltage-gated Ca-channels. Prejunctional autoregulatory mechanisms may also not be altered by indomethacin. As indomethacin inhibits the enzyme cyclooxygenase, it is speculated that endogenously produced prostaglandins exert excitatory actions on gastric smooth muscle, and act mainly postjunctionally to facilitate spontaneous and neurogenic electrical and mechanical activity.

Effects of cyclopiazonic acid on contraction and intracellular Ca2+ in oesophageal striated muscle of normotensive and spontaneously hypertensive rats.

1. The effects of cyclopiazonic acid (CPA), a selective inhibitor of sarcoplasmic reticulum (SR) Ca2+-ATPase, on twitch contraction and on the resting state of tension and intracellular Ca2+ level ([Ca2+]i) of the oesophageal striated muscle of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar Kyoto rats (WKY) were compared. 2. CPA (10 micronM) augmented the twitch contraction of oesophageal striated muscle preparations from both SHRSP and WKY, reducing the rate of relaxation (-dT/dt), and thus resulting in the prolongation of the time to 80% relaxation. The effect was significantly smaller in the SHRSP preparations. 3. In the resting state, CPA caused a sustained elevation of [Ca2+]i. The elevation was greater in the WKY preparations. Tension development accompanied by the elevation was observed in WKY preparations, but not in SHRSP preparations. 4. The sustained elevation of [Ca2+]i induced by CPA was eliminated by the removal of extracellular Ca2+. Both the elevated [Ca2+]i and tension in the preparations from WKY were reduced by flufenamic acid (100 micronM), mefenamic acid (100 micronM), lanthanum (La3+, 100 micronM), gadolinium (Gd3+, 100 micronM) and SK&F 96365 (100 micronM) but not by verapamil (10 micronM). 5. Thapsigargin (3 micronM), another SR Ca2+-ATPase inhibitor, produced similar effects on basal tension to those of CPA, although it reduced the amplitude of twitch contraction. 6. These results suggest that in the rat oesophageal striated muscle, (1) CPA extends the sequestrating time of Ca2+ into the SR, (2) CPA induces a Ca2+ influx mediated through verapamil-insensitive pathways, possibly nonselective cation channels, and (3) the mechanism of [Ca2+](i) modulation due to CPA-sensitive SR Ca2+-ATPase is deteriorated in the oesophageal striated muscle from SHRSP as compared with WKY preparations.

Tight coupling between the rate of rise of Ca 2+ transient and peak twitch contraction in guinea-pig papillary muscle

We evaluated the relationship between cytoplasmic Ca 2+ concentration ([Ca 2+] i) and force in guinea-pig papillary muscles loaded with a fluorescent Ca 2+ indicator, fura-PE3. In the absence of ryanodine, [Ca 2+] i transient and force were altered by changing extracellular Ca 2+ concentration and stimulation frequency, and also by adding methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5-carboxylate (Bay K 8644) or ouabain. Under these conditions, the peak force correlated linearly with the maximal rate of rise of [Ca 2+] i ( γ=0.948) more than the peak [Ca 2+] i transient ( γ=0.737). Ryanodine inhibited the increase in the maximal rate of rise of [Ca 2+] i resulting in abolishment of the correlation between force and the maximal rate of rise of [Ca 2+] i. These results suggest that the maximal rate of rise of [Ca 2+] i reflects Ca 2+ release from the sarcoplasmic reticulum, and this fraction of [Ca 2+] i is crucial for determining the amplitude of twitch contractions when the sarcoplasmic reticulum is intact in guinea-pig papillary muscle.

Involvement of nitric oxide in extrinsic nervous control of ileal contractile activity

The experiments were carried out on guinea pig mesenteric nerve-ileal preparations (ileal segments with mesenteric nerves originating from the superior mesenteric ganglion) isolated at various distances from the ileocecal junction (ICJ). Contractile activity was recorded in the presence of hexamethonium (50 μM). On the background of electrical field stimulation (EFS; 0.1 Hz, 0.5 ms, supramaximal current intensity)-induced twitch contractions, the mesenteric nerve stimulation (MNS; frequency of 2–30 Hz, 0.5 ms, supramaximal current intensity, 20-s trains) exerted two types of effects, depending on the distance from ICJ at which the preparations were isolated and on the pulse frequency. In preparations isolated from the ileum at a distance of 20 cm from ICJ, MNS at all the frequencies studied inhibited the EFS-induced twitch contractions, reaching the maximum at 30 Hz. In preparations isolated from the terminal ileum at a distance of 10 cm from ICJ, MNS at 20 Hz and 30 Hz decreased the twitch contraction amplitude, whereas MNS at 2–10 Hz produced an increase in the tone on which twitch contractions with reduced amplitude were superimposed. The finding that guanethidine (5 μM) eliminated the MNS twitch inhibition provides evidence for the adrenergic origin of the latter. The nitric oxide synthase inhibitor N ω-nitro-L-arginine (100 μM) was efficient in reducing the MNS twitch inhibition but only at low-frequency (5 Hz) MNS (p < 0.05). Our results suggest the participation of nitric oxide in the nervous control exerted by the superior mesenteric ganglion over the ileal contractile activity.

Effects of mercuric chloride and methyl mercury on cholinergic neuromuscular transmission in the guinea-pig ileum.

The effects of mercuric chloride (HgCl2) and methyl mercury (MeHg) were examined on basal mechanical activity and electrically-induced neurogenic cholinergic contractions (twitch contractions) in longitudinal muscle-myenteric plexus strips from guinea-pig distal ileum. Both compounds at 0.33 microM slightly enhanced the amplitude of twitch contractions in approximately 50% preparations. This effect was probably due to facilitation of acetylcholine (ACh) release since 0.1 and 1 microM mercurials increased electrically-evoked tritium outflow from [3H]choline preloaded muscle layer with attached myenteric plexus. Conversely, higher mercury concentrations inhibited twitch contractions (HgCl2 IC50 = 21.3 +/- 6.4 microM; MeHg IC50 = 45.1 +/- 5.5 microM), as well as contractions to exogenous ACh (0.1 microM) in resting preparations, and concomitantly increased the basal tone. The former effects possibly reflected an antimuscarinic activity of mercury, while the latter was related to alterations of calcium homeostasis in the effector cells. Indeed, the effect of HgCl2 on basal tone was antagonized by the Ca2+ entry blocker nifedipine (3, 10, 30 nM), indicating Hg-induced facilitation of Ca2+ influx through voltage-dependent channels. On the whole, our results suggest that cholinergic neuromuscular transmission and Ca(2+)-dependent mechanisms underlying smooth muscle contractility are targets for mercury toxicity in the intestine.

Doxorubicin alters Ca 2+ transients but fails to change Ca 2+ sensitivity of contractile proteins

Doxorubicin produced a transient increase and a subsequent decrease in the amplitude of twitch contraction in myocytes isolated from guinea-pig heart and loaded with fura-2. These changes were associated with an increase and a subsequent decrease, respectively, in the amplitude of Ca 2+ transients (peak minus diastolic Ca 2+ concentrations). Doxorubicin increased the diastolic Ca 2+ concentration with a concomitant shortening of the diastolic myocyte length. The time to peak Ca 2+ transients and the time to peak twitch contraction increased in parallel. Doxorubicin failed to affect the Ca 2+ concentration-contraction curve in skinned fibers obtained from atrial muscle. We conclude that biphasic inotropic effects of doxorubicin result from biphasic changes in Ca 2+ transients, and that doxorubicin fails to alter Ca 2+ sensitivity of contractile proteins. These findings are consistent with the hypothesis that doxorubicin enhances Ca 2+ release and impairs Ca 2+ uptake by the sarcoplasmic reticulum.

Effect of histamine and substance P on the rabbit and human iris sphincter muscle

In an attempt to clarify the functional action of histamine and substance P on atropine-resistant miosis, we isolated rabbit and human iris sphincter muscles and investigated their mechanical properties using the isometric tension recording method. Substance P dose-dependently contracted the rabbit iris sphincter, but had no effect on the human iris sphincter. In the rabbit iris sphincter, histamine reduced the amplitude of twitch contraction evoked by field stimulation but had no effect on carbachol-induced contraction. Thioperamide, but not mepyramine or cimetidine, partially antagonized the histamine-induced reduction in the amplitude of twitch contractions. In the human iris sphincter, on the other hand, histamine dose-dependently provoked contraction and the amplitude of histamine-induced contraction was affected neither by atropine nor by indomethacin. These results provide evidence that histamine has strong contractile effect on the human iris sphincter muscle; the rabbit iris sphincter muscle, however, apparently lacks functional histamine receptors. In rabbits, exogenously applied histamine only activates H3 receptors located on the cholinergic nerve terminal, hence the excitatory neuro-effector transmission is suppressed. Thus, histamine may have an important roles in atropine-resistant miosis in humans, but not in rabbits.

Effects of epithelial cell supernatant on membrane potential and contraction of dog airway smooth muscles.

We investigated the effects of cultured epithelial cells and supernatants on resting membrane potential and excitatory neuroeffector transmission in smooth muscle cells of dog trachea and bronchioles. The mean resting membrane potential of the mucosa-free tracheal smooth muscle cells was -59.5 +/- 1.5 mV (+/- SD). Application of cultured epithelial cells (> 2.5 x 10(5) cells/ml) hyperpolarized the membrane, resulting in a potential of -64.5 +/- 1.7 mV. The supernatant of the cultured epithelial cells also increased the resting membrane potential of the mucosa-free tracheal smooth muscle cells by 4 to 9 mV. These hyperpolarizing actions were not modified by indomethacin (10(-5) M), l-NG-nitroarginine (10(-5) M), or oxyhemoglobin (10(-5) M), but were inhibited by glibenclamide (10(-6) M). The supernatants of the cultured epithelial cells completely or partially suppressed the contractile response of epithelium-denuded bronchioles to electrical field stimulations and suppressed the amplitude of excitatory junction potentials of the trachealis evoked by electrical field stimulations. Indomethacin prevented the inhibitory effect of supernatants on the amplitude of twitch contractions and excitatory junction potentials and markedly suppressed supernatant-associated inhibition of the excitatory neuroeffector transmission. Furthermore, indomethacin with AA861, a lipoxygenase inhibitor, completely suppressed this effect. Our findings suggest that cultured airway epithelial cells spontaneously release at least two factors. One factor selectively modulates the resting membrane potential, and the other inhibits the excitatory neuroeffector transmission.

Importance of sympathetic innervation in the positive inotropic effects of bradykinin and ramiprilat.

Isolated rat left atria or right ventricular strips were electrically stimulated at a constant frequency. The amplitude of twitch contractions, thus elicited, rose as a function of stimulation intensity because of increases in the evoked release of sympathetic catecholamines. Bradykinin had no effect on contractile force in preparations paced at a minimal intensity (threshold). By contrast, bradykinin (1 nmol/L to 1 mumol/L) markedly increased twitch contractile force when the preparations were paced at a high intensity (two to three times threshold). The EC50 for the positive inotropic action of bradykinin averaged 42 nmol/L. Ramiprilat (1 mumol/L), an angiotensin I-converting enzyme/kinase II inhibitor, shifted the EC50 for bradykinin to approximately 2 nmol/L. Ramiprilat (1 mumol/L) per se also produced a modest positive inotropic effect. The effects of bradykinin and/or ramiprilate were inhibited by HOE 140 (300 nmol/L), a bradykinin B2-receptor antagonist. Propranolol (1 mumol/L), a beta-adrenoceptor blocker, abolished the effects of bradykinin. After the destruction of sympathetic nerve endings by use of 6-hydroxydopamine, bradykinin no longer exerted a positive inotropic action. Cocaine (10 micrograms/mL), an inhibitor of catecholamine reuptake, potentiated the effect of bradykinin. Bradykinin did not affect the positive inotropic response to tyramine (10 mumol/L), whereas cocaine blocked it. Furthermore, bradykinin did not modify the dose-response curves for added norepinephrine. omega-Conotoxin (100 nmol/L) inhibited the positive inotropic effect of intensified stimulation and bradykinin potentiation. Bradykinin is suggested to facilitate the evoked release of sympathetic catecholamines and thereby cause a positive inotropic effect.

Effects of Procaterol, a Beta-2-Adrenoceptor Stimulant, on Neuroeffector Transmission in Human Bronchial Tissue

It has been reported that low concentrations of noradrenaline or isoprenaline reduce the resting tension of the smooth muscle cells and suppress acetylcholine release from the vagal nerve terminals through activation of beta 2-adrenoceptors. Procaterol, beta 2-adrenoceptor stimulant, has a high potency and selectivity for airway smooth muscle tissues. However, there is little documentation on the prejunctional actions of this chemical in airway smooth muscle, especially in man. In the present study, the effects of procaterol on excitatory neuroeffector transmission in the human bronchus were investigated. Procaterol (10(-10) to 10(-7) M) dose dependently reduced the amplitude of the contractions evoked by electrical field stimulation in the presence of indomethacin (10(-5) M), FPL-55712 (10(-6) M), and guanethidine (10(-6) M). By contrast, procaterol (10(-10) to 10(-9) M) had no effect on the postjunctional response of smooth muscle cells to exogenously applied acetylcholine. Pretreatment with ICI-118551 (10(-7) M), a beta 2-adrenoceptor-blocking agent, reduced the inhibitory action of procaterol on the amplitude of twitch contractions evoked by field stimulations in the human bronchus. These results indicate that procaterol at low concentrations has a prejunctional action, inhibiting the excitatory neuroeffector transmission and presumably suppressing transmitter release from the vagal nerve terminals through beta 2-adrenoceptors in the human bronchial tissue. The prejunctional action of procaterol explains partly its potent bronchodilator effects in clinical use.

Pre-junctional inhibitory action of prostaglandin E 2 on excitatory neuro-effector transmission in the human bronchus

The effects of prostaglandin E 2 (PGE 2) and indomethacin on excitatory neuro-effector transmission in the human bronchus were investigated by tension recording and microelectrode methods. PGE 2 (10 −10–10 −9M) suppressed the amplitude of twitch contractions and excitatory junction potentials (e.j.ps) evoked by field stimulation at a steady level of basal tension obtained by the combined application of indomethacin (10 −5M) and FPL55712 (10 −6M). In doses over 10 −8M, PGE 2 reduced the muscle tone and dose-dependently suppressed the amplitude of twitch contractions. Indomethacin (10 −5 or 5 × 10 −5M) reduced the muscle tone and enhanced the amplitude of twitch contractions and e.j.ps evoked by field stimulation in the presence of FPL55712. PGE 2 (10 −9M) had no effect on the post-junctional response of smooth muscle cells to exogenously applied acetylcholine (ACh) (4 × 10 −7M). However, indomethacin (10 −5M) significantly enhanced the ACh-induced contraction of the human bronchus. These results indicate that PGE 2 in low concentrations has a pre-junctional action to inhibit excitatory neuro-effector transmission in addition to a post-junctional action, presumably by suppressing transmitter release from the vagus nerve terminals in the human bronchial tissues.

Neurophysiology of fastest voluntary muscle contraction in hereditary neuropathy

In patients with hereditary motor and sensory neuropathy types I (demyelinative) and II (neuronal) and in normal subjects, isometric force and electromyographic activity of the first dorsal interosseous muscle were recorded during fastest voluntary contractions and during twitches evoked by nerve stimulation. The maximum voluntary force of the first dorsal interosseous muscle was also measured. In patients, fastest voluntary contraction time (i.e., time from onset of contraction to peak force) was prolonged and inversely proportional to maximum voluntary force. Maximum rate of rise of tension (i.e., slope of rise in force) was reduced and directly proportional to maximum voluntary force. In patients with hereditary motor and sensory neuropathy type I, contraction time was longer and the maximum rate of rise of tension was lower than in those with hereditary motor and sensory neuropathy type II. In patients and normal subjects, voluntary contraction time was closely correlated with the duration of electromyographic bursts. In patients, the twitch contraction time was prolonged and inversely proportional to maximum voluntary force. Twitch contraction amplitude was diminished and directly proportional to maximum voluntary force. Neither twitch contraction time nor amplitude were dependent on the type of hereditary motor and sensory neuropathy. Twitch contraction time evoked by proximal nerve stimulation was minimally longer than that evoked by distal stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

An examination of the putative σ‐receptor in the mouse isolated vas deferens

1. The effects of several ligands which interact with the sigma-binding site were studied on the electrically-evoked (0.1 Hz) neurogenic twitch contractions of the mouse isolated vas deferens. 2. (+)-3-(3-Hydroxyphenyl)-N-(1-propyl)piperidine [+)-3-PPP) (10(-8) - 10(-5) M), inhibited the neurogenic twitch contractions. This inhibitory action was unaffected by naloxone (10(-6)M), idazoxan (10(-6)M), cocaine (10(-6)M) or tyramine (10(-4)-3 x 10(-4)M), but was abolished by the dopamine D2-antagonist, sulpiride (10(-6)M). Therefore, in order to study the potentiating actions of sigma ligands, sulpiride (10(-6)M) was used to prevent any inhibitory actions mediated via dopamine D2-receptors. 3. In the presence of sulpiride (10(-6)M), haloperidol (10(-6)-10(-5)M), (+)-3-PPP (10(-6)-3 x 10(-4) M) and (+)-N-allyl-N-normetazocine [+)-SKF 10,047) (10(-5)-10(-4)M) each reversibly potentiated the neurogenic twitch contractions in a concentration-dependent manner. The rank order of potency was haloperidol greater than (+)-3-PPP greater than (+)-SKF 10,047. 4. The stereoisomers of 3-PPP displayed stereoselectivity with (+)-3-PPP being more potent than (-)-3-PPP. 5. At a concentration that did not potentiate the twitch contractions, (3 x 10(-7)M), haloperidol did not antagonize the potentiating action of (+)-3-PPP (3 x 10(-5)M). 6. 1,3-Di-O-tolyguanidine (DTG) (10(-8)-10(-5)M) had no effect on the amplitude of twitch contractions and did not affect the potentiating action of (+)-3-PPP (10(-5)-3 x 10(-5)M). 7. It is concluded that a-ligands potentiate neurogenic twitch contractions of the mouse isolated vas deferens via a site that is different from the central sigma-binding site.