Low-frequency Electrical Field Stimulation Research Articles

Nerve-induced responses of mouse vaginal smooth muscle.

Neural and agonist-induced contractions of proximal (i.e. upper half adjacent to the cervix) and distal mouse vaginal smooth muscle strips were investigated. We hypothesised that nerve-mediated vaginal contractions arise through activity of cholinergic nerves. Nerve activation by bursts of electrical field stimulation (EFS) caused a primary transient contraction often accompanied by a secondary transient contraction, both larger in proximal than distal tissues (i.e. primary: 7-fold larger; secondary: 3-fold larger). Our hypothesis was supported as we found that cholinergic nerves mediated the primary transient contraction in both proximal and distal vaginal strips, as EFS responses were enhanced by neostigmine an anticholinesterase, massively inhibited by the competitive muscarinic receptor antagonist atropine and not affected by the non-selective α-adrenergic receptor antagonist phentolamine. Primary transient contractions were halved in amplitude by the L-type Ca2+ channel blocker nifedipine and markedly inhibited by the sarco-endoplasmic reticulum calcium ATPase (SERCA) inhibitor cyclopiazonic acid (CPA). Resultant secondary transient contractions were abolished by nifedipine. Notably, the selective α1-adrenergic receptor agonist phenylephrine caused tonic contracture in distal but not proximal strips. Low-frequency EFS often initiated recurrent transient contractions similar to those elicited by CCh. Immunohistochemical studies demonstrated innervation of the smooth muscle. Findings of enhanced proximal cholinergic nerve-induced transient contractions, evidence that maintained nerve stimulation could cause recurrent contractions and the finding of distal phenylephrine-mediated tonic contraction have implications on insemination.

MLCK and PKC Involvements via Gi and Rho A Protein in Contraction by the Electrical Field Stimulation in Feline Esophageal Smooth Muscle

We have shown that myosin light chain kinase (MLCK) was required for the off-contraction in response to the electrical field stimulation (EFS) of feline esophageal smooth muscle. In this study, we investigated whether protein kinase C (PKC) may require the on-contraction in response to EFS using feline esophageal smooth muscle. The contractions were recorded using an isometric force transducer. On-contraction occurred in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME), suggesting that nitric oxide acts as an inhibitory mediator in smooth muscle. The excitatory composition of both contractions was cholinergic dependent which was blocked by tetrodotoxin or atropine. The on-contraction was abolished in Ca(2+)-free buffer but reappeared in normal Ca(2+)-containing buffer indicating that the contraction was Ca(2+) dependent. 4-aminopyridine (4-AP), voltage-dependent K(+) channel blocker, significantly enhanced on-contraction. Aluminum fluoride (a G-protein activator) increased on-contraction. Pertussis toxin (a G(i) inactivator) and C3 exoenzyme (a rhoA inactivator) significantly decreased on-contraction suggesting that Gi or rhoA protein may be related with Ca(2+) and K(+) channel. ML-9, a MLCK inhibitor, significantly inhibited on-contraction, and chelerythrine (PKC inhibitor) affected on the contraction. These results suggest that endogenous cholinergic contractions activated directly by low-frequency EFS may be mediated by Ca(2+), and G proteins, such as Gi and rhoA, which resulted in the activation of MLCK, and PKC to produce the contraction in feline distal esophageal smooth muscle.

Characterization of the Off Response to Electrical Field Stimulation in Gallbladder Smooth Muscle

Background. Low-frequency electrical stimulation of intramural nerves of gut smooth muscle produces an “off response,” that is, a contraction that occurs after electrical field stimulation (EFS) of the intramural nerves is stopped. The off response coincides with a depolarization of the muscle following an EFS-induced hyperpolarization of that muscle. The aims of our study were to determine if the off response is present in gallbladder smooth muscle and to determine the mechanisms involved in this nerve-mediated response.Materials and methods. Gallbladder strips from opossums were placed in Krebs solution and passed through bipolar ring electrodes for EFS of intramural nerves, and isometric force measurements were recorded. Dose–response curves were determined with NG-nitro-l-arginine (l-NNA) a competitive inhibitor of nitric oxide (NO) synthase; 1H-[1,2,4]oxadiazolol[4,3a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase; and oxyhemoglobin, a scavenger of nitric oxide.Results. A contraction termed the off response occurred shortly after EFS ended. The off response was abolished with tetrodotoxin and atropine. The amplitude of the off response increased with increasing voltage. The amplitude of the off response decreased by 41% with l-NNA 1.5 mM. Preincubation of the tissue with l-arginine (1 mM) prevented the inhibition of amplitude seen with l-NNA. The amplitude of the off response decreased by 43% with oxyhemoglobin (40 μM) and by 56% with ODQ (250 μM).Conclusion. We conclude that the off response is present in gallbladder smooth muscle after low-frequency EFS. NO may be a mediator of this off response and of nonadrenergic noncholinergic responses in gallbladder smooth muscle.

Cholinergic modulation of non-adrenergic, non-cholinergic relaxation in isolated, small coronary arteries from lambs.

The presence of cholinergic innervation of small coronary arteries in the lamb was investigated by measuring choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities and by performing in vitro experiments in a microvascular myograph to establish whether or not there is a cholinergic component in the response to electrical field stimulation (EFS). ChAT-specific activity was present in proximal coronary segments, but was significantly higher in small coronary arteries. AChE-positive ganglia and fibres were distributed within the adventitia and outer third of the media in proximal coronary segments, and dense perivascular nerve plexuses were observed in small coronary arteries. Acetylcholine induced contractions in all preparations examined and relaxations in 20% of the segments contracted with the thromboxane analogue U46619. EFS did not induce neurogenic contractions in lamb small coronary arteries. In the presence of the alpha-adrenoceptor antagonist, phentolamine, EFS caused frequency-dependent reproducible relaxations that were enhanced by the blocker of cholinergic transmission, botulinum neurotoxin. An inhibitor of AChE, physostigmine, had no significant effect on the relaxations caused by EFS, while both the muscarinic receptor antagonist, atropine, and the muscarinic M2-receptor antagonist, AFDX 116, enhanced these responses. Blockade of sympathetic neurotransmission with guanethidine or incubation with the P2-receptor antagonist, suramin, abolished the relaxations induced by EFS, whereas propranolol was without effect. Low-frequency EFS caused less relaxation in preparations activated by acetylcholine than in those contracted with U46619, while sensitivity and maximal relaxation induced by adenosine 5'-triphosphate (ATP) were not different in U46619- and acetylcholine-contracted arteries. The presence of the enzymes necessary for both biosynthesis and degradation of acetylcholine and the finding that blockers of cholinergic neurotransmission enhance EFS-induced relaxations suggest that small coronary arteries are cholinergically innervated.

Somatostatin excites canine ileum ex vivo: role for nitric oxide?

Isolated perfused segments of canine ileum have no spontaneous motor activity and release large quantities of vasoactive intestinal polypeptide (VIP) continuously. Somatostatin perfusion was shown to decrease VIP release, accompanied by increased contractions and amplification of responses to low-frequency electrical field stimulation. After perfusion of higher somatostatin concentrations, the VIP output did not recover but quiescence returned. The actions of somatostatin on motor activity were not modified by hexamethonium, slightly reduced by atropine, and markedly reduced by tetrodotoxin. Inhibition of VIP output was not the major determinant of motor activity in the ileum because 1) a second infusion of somatostatin had similar motor effects despite markedly reduced VIP output, 2) abolition of tonic VIP output did not prevent induction of motor activity by somatostatin, and 3) artificial restoration of VIP levels did not prevent or antagonize somatostatin-induced ileal contractions. In contrast, the increment in motor responses induced by somatostatin was not apparent after N omega-nitro-L-arginine methyl ester, an inhibitor of nitric oxide (NO) synthase, but recovered after reversal by L-arginine. We conclude that the mode of somatostatin activation of intestinal motor activity involves reduced NO output, enhanced excitatory mediator action or release, a direct action on smooth muscle, and possibly inhibition of VIP output. Of these, reduced NO output plays the most important role.

Effects of cobalt or nickel on the sympathetically mediated contractile responses in rat-isolated vas deferens.

Subchronic (30 days) exposure of rats to Co(NO3)2 or NiSO4 (20 mg.kg-1) in drinking water caused suppression of the isolated vas deferens contractile responses to exogenous adenosine 5'-triphosphate (ATP), noradrenaline, and l-phenylephrine, shifting the concentration-response curves to the relevant agonist to the right. Both metals facilitated the alpha 1-adrenoceptor antagonistic effects of prazosin, which resulted in increased pA2 values for the drug (9.68 +/- 0.13 in controls vs. 10.15 +/- 0.12 in Co(2+)-treated preparations and 12.60 +/- 0.67 in Ni(2+)-treated preparations). The inhibitory effect of clonidine on the contractions in response to low-frequency electrical field stimulation (EFS) in metal-treated preparations was decreased with pD2 values: 10.52 +/- 0.04 in controls, 9.56 +/- 0.13 in Co(2+)-treated preparations and 9.92 +/- 0.16 in Ni(2+)-treated preparations. The monophasic contractile responses to low-frequency EFS (0.1 Hz, 1 ms, 80 V) as well as the first phase of the biphasic contractions after high-frequency long-lasting EFS (300 pulses, 0.1 ms, 40 V, at 4, 8 or 20 Hz) were significantly increased in both groups of heavy metal-treated preparations. Therefore, subchronic exposure to Co2+ or Ni2+ leads to changes in pre- and postjunctional mechanisms underlying the sympathetically mediated contractile activity of isolated rat vas deferens.

Muscarinic receptor subtypes in equine tracheal smooth muscle.

Selective muscarinic receptor antagonists were used to identify muscarinic receptor subtypes in equine trachealis strips. The M1 receptor antagonist pirenzepine (10(-7) mol/L to 3 x 10(-5) mol/L) and the M3 receptor antagonist 4-diphenylacetoxy-N-methylpiperidine (4-DAMP, 10(-9) mol/L to 3 x 10(-7) mol/L3) dose dependently inhibited the contractile responses to electrical field stimulation (EFS) and exogenous acetylcholine (ACh). Schild plots yielded a pA2 value for pirenzepine vs ACh of 6.75 +/- 0.09, which is consistent with the affinity for M2 or M3 receptors, and a pA2 value for 4-DAMP vs ACh of 8.47 +/- 0.09, which is in agreement with the affinity for M3 receptors. The M2 receptor antagonist gallamine (10(-5) mol/L and 10(-4) mol/L) did not affect the response of trachealis to exogenous ACh and low-frequency EFS (0.1-2 Hz) but decreased the responses to high-frequency EFS (4-16 Hz). These results suggest that the muscarinic receptors mediating contractions induced by ACh in equine tracheal smooth muscle are of the M3 subtype. The lack of an increase in the response to EFS following gallamine suggests that functional prejunctional inhibitory M2 receptors are not present on the cholinergic nerves innervating equine tracheal smooth muscle.

In‐vitro contractile response of the rabbit corpus cavernosa to field stimulation and autonomic agonists and antagonists: A qualitative study

AbstractField stimulation of rabbit corporus cavernosum tissue strips can result in relaxation, contraction, or a biphasic response depending on the frequency and the power utilized. In this study we characterized the autonomic components of this response by exposing corporal tissue strips to a variety of autonomic agonists and antagonists including phentolamine, isoproterenol, methoxamine, propranolol, bethanechol, atropine, and ATP. Low frequency electrical field stimulation produced a bi‐phasic response characterized by an initial relaxation followed by a contraction. High frequencies (≥ 32 Hz) produced contraction only. All responses were abolished by tetrodotoxin, indicating that both the contractile and relaxant responses to field stimulation are mediated by complex neural mechanisms. The initial relaxation response involves a combination of mediators which include musca‐rinic cholinergic stimulation, purinergic, beta‐adrenergic, and non‐adrenergic, non‐cholinergic (NANC) stimulation. The non‐cholinergic contribution to corporal smooth muscle relaxation appeared to be approximately equal in significance to the cholinergically mediated relaxation. Beta adrenergic stimulation mediated a direct relaxation of the corporal smooth muscle. The contractile portion of the bi‐phasic response was mediated by alpha‐adrenergic stimulation. Additionally we have noted a rebound contraction following termination of field stimulation at all frequencies that is not affected by adrenergic or cholinergic blockade and may reflect the field‐stimulated release of an endogenous smooth muscle contractile factor.

Selective depletion of the acetylcholine and vasoactive intestinal polypeptide of the guinea-pig myenteric plexus by differential mobilization of distinct transmitter pools.

The effect of electrical field stimulation on the release of acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) from superfused strips of myenteric plexus-longitudinal muscle (MPLM) of guinea-pig ileum and on the transmitter content of the tissue was investigated at different frequencies and in the presence and absence of choline hemicholinium-3 and colchicine. Low frequency electrical field stimulation released ACh by more than 4 times the basal release; the simultaneously detected VIP secretion was increased only slightly above the resting level. During high frequency stimulation (50 Hz) the release of VIP was greatly increased (to 5 times the resting release) whereas the release of ACh increased to only 150% of the basal output. When choline was present, the ACh content of the tissue itself was not altered by electrical stimulation indicating a rate of synthesis sufficient to maintain release. It was reduced in a frequency-dependent manner in the absence of exogenous choline or in the presence of 10 microM hemicholinium-3 (an inhibitor of choline uptake) by up to 54% of the original content. A similar but even larger reduction took place in the amount of ACh released. Neither the secretion of VIP nor the tissue VIP content was altered by these treatments. Long-lasting (greater than 60 min) high-frequency (50 Hz) stimulation resulted in the depletion of the VIP pool (by 25%) while the ACh content remained unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)