Evidence for participation of nitric oxide in excitatory neurotransmission in rat vas deferens

The effects of Tityus bahiensis scorpion venom on the contractility of jejunum, vas deferens, and the aorta is differentially affected by tetrodotoxin

The pharmacological effects of the crude venom of the scorpion Tityus serrulatus or its isolated toxins have been widely studied. However, few studies are available on Tityus bahiensis venom. We recently discovered that T. serrulaus venom leads to the release of tetrodotoxin-resistant acetylcholine. Thus, our objective was to verify whether T. bahiensis venom could have a similar action in the jejunum. Furthermore, we evaluated the possibility that this action occur in other tissues innervated by the autonomic nervous system. Thus, organ bath studies were conducted to evaluate the contractile and relaxant effects of venom on the jejunum, vas deferens and aorta of rats in the presence or absence of tetrodotoxin. We observed that jejunum, vas deferens and aorta contracted when the T. bahiensis venom was applied. In the jejunum, the venom reveals a contractile component resistant to tetrodotoxin. It also was able to relax pre-contracted preparations of jejunum and aorta but not vas deferens. Only in the aorta, the relaxation was resistant to tetrodotoxin. The effects of scorpion venoms are attributed to its action on ionic channels leading to neuronal depolarization and neurotransmitter release. Our results indicated that a similar mechanism is present in the observed effects of the venom. However, another mechanism must be present in the venom-induced contraction in the jejunum and relaxation in the aorta. Possible involvement of tetrodotoxin-resistant sodium channels or non-neuronal release of neurotransmitters is discussed. We emphasize that the study of the Tityus scorpion's venom, especially T. bahiensis, is of great importance because it can unveil unknown pharmacological and physiological mechanisms of excitable cells.

Relationship between central behavioral effects and peripheral sympathetic neurotransmission functionality during acute cocaine withdrawal syndrome in adult rats

BACKGROUND

Acute cocaine withdrawal syndrome (ACWS) is characterized as a set of organic alterations triggered by abrupt discontinuation of chronic cocaine consumption, usually occurring at 24-40 hours after withdrawal. However, little is known about the relationship between central and peripheral sympathetic neurotransmission during ACWS.

OBJECTIVE AND METHODS

We investigated the mechanisms involved in central and peripheral sympathetic neurotransmission and how ACWS affects the sympathetic functionality. Cocaine was administered twice daily for 5 days in Wistar rats (at least 5 in each group): on the first and second day, 15 mg/kg/i.p.; third day, 20 mg/kg/i.p.; and finally in the last two days, 30 mg/kg/i.p. Subsequently, at 1, 24, 48 and 120 h after cocaine administration the following experiments were done: (i) at the central level, behavioral tests of open-field and elevated plus maze; and (ii) at the peripheral level, tests of catecholamine release, function of α2-adrenergic receptors (α2-ARs), imidazoline receptors (I(1,2)-Rs), L-type voltage-gated (Ca(v1.2)) Ca(2+) channels and α1-ARs.

RESULTS

During ACWS, rats showed hypolocomotion and exacerbation of anxiogenic-effects 24 h after cocaine withdrawal. Likewise, a decrease in the catecholamine release and activity of α2-ARs/I(1,2)-Rs at 24-48 h after cocaine withdrawal was observed. A decrease in Ca(v1.2) channels and α1-ARs function at 48 h after cocaine withdrawal was observed.

CONCLUSIONS

The relationship of central and peripheral sympathetic neurotransmission during ACWS possibly due to a failure in activation and/or inactivation of presynaptic α2-ARs/I(1,2)-Rs, may offer a potential target for attenuating ACWS.

Influence of acute treatment with sibutramine on the sympathetic neurotransmission of the young rat vas deferens

The effects of acute treatment with sibutramine on the peripheral sympathetic neurotransmission in vas deferens of young rats were still not evaluated. Therefore, we carried out this study in order to verify the effects of acute sibutramine treatment on the neuronal- and exogenous agonist-induced contractions of the young rat vas deferens. Young 45-day-old male Wistar rats were pretreated with sibutramine 6 mg/kg and after 4h the vas deferens was used for experiment. The acute treatment with sibutramine was able to increase the potency (pD2) of noradrenaline and phenylephrine. Moreover, the efficacy (Emax) of noradrenaline was increased while the efficacy of serotonin and nicotine were decreased. The maximum effect induced by a single concentration of tyramine was diminished in the vas deferens from treated group. Moreover, the leftward shift of the noradrenaline curves promoted by uptake blockers (cocaine and corticosterone) and β-adrenoceptor antagonist (propranolol) was reduced in the vas deferens of treated group. The initial phasic and secondary tonic components of the neuronal-evoked contractions of vas deferens from treated group at the frequencies of 2 Hz were decreased. Moreover, only the initial phasic component at 5 Hz was diminished by the acute treatment with sibutramine. In conclusion, we showed that the acute treatment with sibutramine in young rats was able to affect the peripheral sympathetic nervous system by inhibition of noradrenaline uptake and reduction of the neuronal content of this neurotransmitter, leading to an enhancement of vas deferens sensitivity to noradrenaline.

Vas deferens neuro-effector junction: from kymographic tracings to structural biology principles

The vas deferens is a simple bioassay widely used to study the physiology of sympathetic neurotransmission and the pharmacodynamics of adrenergic drugs. The role of ATP as a sympathetic co-transmitter has gained increasing attention and furthered our understanding of its role in sympathetic reflexes. In addition, new information has emerged on the mechanisms underlying the storage and release of ATP. Both noradrenaline and ATP concur to elicit the tissue smooth muscle contractions following sympathetic reflexes or electrical field stimulation of the sympathetic nerve terminals. ATP and adenosine (its metabolic byproduct) are powerful presynaptic regulators of co-transmitter actions. In addition, neuropeptide Y, the third member of the sympathetic triad, is an endogenous modulator. The peptide plus ATP and/or adenosine play a significant role as sympathetic modulators of transmitter's release. This review focuses on the physiological principles that govern sympathetic co-transmitter activity, with special interest in defining the motor role of ATP. In addition, we intended to review the recent structural biology findings related to the topology of the P2X1R based on the crystallized P2X4 receptor from Danio rerio, or the crystallized adenosine A2A receptor as a member of the G protein coupled family of receptors as prototype neuro modulators. This review also covers structural elements of ectonucleotidases, since some members are found in the vas deferens neuro-effector junction. The allosteric principles that apply to purinoceptors are also reviewed highlighting concepts derived from receptor theory at the light of the current available structural elements. Finally, we discuss clinical applications of these concepts.

Functional effects of alcohol withdrawal syndrome on peripheral sympathetic neurotransmission in vas deferens of adult rats

AIMS

Alcohol withdrawal syndrome (AWS) is characterized by a set of physiological modifications triggered by abrupt withdrawal and/or decreasing consumption of ethanol (EtOH), which may manifest 16-48 h after ceasing consumption. The relationship between the effects of AWS and central and peripheral sympathetic neurotransmission is unknown. This study investigates the possible mechanisms on the sympathetic system during periods of AWS.

MAIN METHODS

Male Wistar rats were treated with EtOH (6-10 g/kg/day/v.o. 5 days). Subsequently, 1h, 24h, 48 h and 120 h after administration of the last dose of EtOH, the animals were sacrificed, and their vas deferens (VD) were removed to perform the following evaluations: (a) concentration-effect curves of sympathetic agonist; (b) activity of α2-adrenoreceptor; (c) function of voltage-dependent calcium channels (Cav); and (d) release of endogenous catecholamines measured in real time coupled to HPLC.

KEY FINDINGS

The results showed that the maximum effects of contraction were increased by agonists tested in at 24h and 48 h EtOH withdrawal. The inhibitory affinity (pIC50) of guanfacine was decreased 24h EtOH withdrawal. The function of Cav was also decreased as pIC50 values dropped 24h and 48 h EtOH withdrawal. The release of catecholamines increased 48 h after EtOH withdrawal. It is suggested that AWS triggers hyperactivity in peripheral sympathetic neurotransmission.

SIGNIFICANCE

The mechanisms underlying hyperactivity are possibly explained by a failure of autoregulation from catecholamines released by α2-adrenoreceptors and/or an increase of Cav function, which may be potential targets to attenuate the symptoms of AWS at the peripheral level.

Vas deferens smooth muscle responses to the nitric oxide-independent soluble guanylate cyclase stimulator BAY 41-2272

The nitric oxide-cGMP signaling pathway modulates the ejaculatory functions. The nitric oxide (NO)-independent soluble guanylate cyclase haem-dependent stimulator BAY 41-2272 potently relaxes different types of smooth muscles. However, no study investigated its effects in vas deferens smooth muscle. Therefore, we designed experiments to evaluate the in vitro relaxing responses of vas deferens to BAY 41-2272. The effects of prolonged oral intake with BAY 41-2272 in vas deferens contractions of rats treated chronically with the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) were also investigated. BAY 41-2272 (0.001-100 μM) produced concentration-dependent relaxations in the prostatic and epididymal portions of vas deferens, an effect markedly reduced by the soluble guanylate cyclase inhibitor ODQ (100 μM). BAY 41-2272 significantly increased cGMP levels that were fully prevented by ODQ. In separate protocols, rats received L-NAME (20mg/rat/day) concomitantly with BAY 41-2272 (10mg/kg/day, 4 weeks), after which vas deferens contractions to electrical-field stimulation and noradrenaline were achieved. Electrical-field stimulation (1-32 Hz) evoked frequency-dependent contractions that were significantly enhanced in L-NAME-treated rats. Co-treatment with BAY 41-2272 fully reversed the increased contractile responses in L-NAME group. Noradrenaline (0.01-100 μM)-induced contractions were also greater in L-NAME-treated rats, and that was normalized by BAY 41-2272. In conclusion, BAY 41-2272 potently relaxes in vitro rat vas deferens smooth muscle and elevates the cGMP levels in an ODQ-sensitive manner. Moreover, prolonged oral intake with BAY 41-2272 restores the enhanced contractile vas deferens activity in rats treated with L-NAME. NO-independent soluble guanylate cyclase stimulators may be an alternative treatment for premature ejaculation.

Effects of novel tacripyrines ITH12117 and ITH12118 on rat vas deferens contractions, calcium transients and cholinesterase activity

We have recently synthesized a new series of hybrid compounds having the moieties of tacrine, a potent inhibitor of brain and peripheral acetylcholinesterase (AChE), and nimodipine, a blocker of L-type voltage-dependent calcium channels (VDCCs). These compounds were designed to target AChE and L calcium channels in the brain, as potential therapeutic agents in Alzheimer's disease. We performed the present study to determine the main peripheral side effects of two of these compounds, ITH12117 and ITH12118. We have here shown that in rat vas deferens these compounds inhibited AChE with a potency about 1000-fold lower than that of physostigmine or tacrine. Furthermore, the hybrid compounds enhanced contractions evoked by acetylcholine, with a potency about 100-fold lower than that of physostigmine or tacrine. Additionally, contractions induced by Ca2+ on depolarized vas deferens were blocked by nimodipine with greater efficacy, compared with ITH12117 and ITH12118. Compound ITH12118 (1 μM) caused a pronounced inhibition of the tonic (but not phasic) contraction elicited by electrical field stimulation. Furthermore, the same dose of nimodipine and ITH12118 blocked by 75% cytosolic Ca2+ elevations produced by acetylcholine, noradrenaline, or ATP. As a matter of comparison, we showed that rat brain cortex AChE was inhibited by ITH12118 with a potency 10 to 20-fold higher than that for vas deferens. This study shows that ITH12118 could be a paradigmatic multitarget compound having selective brain effects with smaller peripheral side effects. This may help to orient the search of new neuroprotective compounds with potential therapeutic application in Alzheimer's disease.

Functionomics: the analysis of a postgenomic concept on the basis of pregenomic pharmacological studies in smooth muscle

The term functionomics (Amin 2003, Neumann et al. 2004) refers to a postgenomic integrated Systems Biology (Attur et al. 2002) using a multidimensional approach for cells, tissues and organs. It considers current or future involvement among genomics, proteomics or metabolomics, including the main factors that cause biological responses and modulation under different conditions. Our objective in the present review is to summarize the contemporary understanding of functionomics of smooth muscle pharmacology, based on the results obtained on the pregenomic era during several years in our laboratory. The present approach is based on the knowledge of the dynamics of the receptor system, which comprises a cascade of phenomena, leading from the drug administration to the final biological response. We will describe several conditions in which the final effect is modified, based on perturbations induced on drug absorption, distribution, metabolism, interaction with receptors and mobilization of second messengers, as well as by interactions with a second receptor system. We will also discuss the gaps that need to be fulfilled in order to obtain a clear and better understanding of the receptor system in smooth muscle, and to narrow the bridge between ourknowledge of the function of biological systems, genomics, and other recently introduced areas.

Mechanisms of adaptive supersensitivity in vas deferens

Adaptive supersensitivity is a phenomenon characteristic of excitable tissues and discloses as a compensatory adjustment of tissue's response to unrelated stimulatory endogenous and exogenous substances after chronic interruption of excitatory neurotransmission. The mechanisms underlying such higher postjunctional sensitivity have been postulated for a variety of cell types. In smooth muscles, especially the vas deferens with its rich sympathetic innervation, the mechanisms responsible for supersensitivity are partly understood and appear to be different from one species to another. The present review provides a general understanding of adaptive supersensitivity and emphasizes early and recent information about the putative mechanisms involved in this phenomenon in rodent vas deferens.

Evidence for the participation of calcium in non-genomic relaxations induced by androgenic steroids in rat vas deferens

BACKGROUND AND PURPOSE

Androgens cause non-genomic relaxation in several smooth muscle preparations. However, such an effect has not been investigated in rat vas deferens yet. Our purpose was to study the effect of testosterone and derivatives in this tissue.

EXPERIMENTAL APPROACH

The influence of androgens was tested on contraction and translocation of intracellular Ca(2+) induced by KCl in rat vas deferens in vitro.

KEY RESULTS

The testosterone derivative 5alpha-dihydrotestosterone produced a rapid and reversible concentration-dependent relaxation of KCl-induced contractions. Other androgens were also effective, showing the following rank order of potency: androsterone >5beta-dihydrotestosterone >androstenedione >5alpha-dihydrotestosterone >testosterone. Calcium-induced contractions were also inhibited (about 45%) by 5alpha-dihydrotestosterone (30 microM). Moreover 5alpha-dihydrotestosterone blocked the increase of intracellular Ca(2+) induced by KCl, measured by the fluorescent dye fura-2. Relaxation to 5alpha-dihydrotestosterone was resistant to the K(+) channel antagonists glibenclamide, 4-aminopyridine and charybdotoxin. It was not affected by removal of epithelium or by L-NNA (300 microM), an inhibitor of nitric oxide biosynthesis, nor by selective inhibitors of soluble guanylate cyclase, ODQ or LY 83583, indicating that nitrergic or cGMP mediated mechanisms were not involved. The androgen-induced relaxation was also not blocked by the protein synthesis inhibitor cycloheximide (300 microM) or by the classical androgen receptor flutamide (up to 100 microM), corroborating that the effect is non-genomic.

CONCLUSIONS AND IMPLICATIONS

Testosterone derivatives caused relaxation of the rat vas deferens, that did not involve epithelial tissue, K(+) channels, or nitric oxide-dependent mechanisms, but was related to a partial blockade of Ca(2+) influx.

Nitric oxide modulates biphasic contractile response of guinea pig vas deferens to electrical field stimulation

Electrical field stimulation (EFS) produced a biphasic contractile response; viz. initial rapid phasic contraction and second slow tonic contraction, in isolated guinea pig vas deferens. Pretreatment with the substrate of nitric oxide (NO) synthase (NOS), 1 mM L-arginine (L-ARG), augmented both the initial rapid and the second slow contractile responses to EFS (5 Hz, 0.5 msec, 30 V, for 30 sec). The increase of stimulation frequency from 5 Hz to 10 Hz or 20 Hz tended to attenuate the augmented responses. On the contrary, pretreatment with an inhibitor of NOS, 0.1 mM NG-nitro-L-arginine (L-NNA) suppressed both the initial rapid and the second slow contractile responses to EFS. The suppressive effect on the initial rapid contraction was also attenuated by the increase of stimulation frequency from 5 Hz or 10 Hz to 20 Hz. Contractile response to exogenously administered 1 mM adenosine triphosphate (ATP) tended to be slightly increased and decreased by the treatment with 1 mM L-ARG and 0.1 mM L-NNA, respectively. Contractile response to exogenously administered 10 microM noradrenaline (NA) was almost unaffected by the treatment with 1 mM L-ARG, while the treatment with 0.1 mM L-NNA slightly depressed the response. Potentiated contractile response to 1 mM ATP in the presence of 10 microM NA was further potentiated by the treatment with 1 mM L-ARG, while the response was almost unaffected by the treatment with 0.1 mM L-NNA. These findings may indicate that NO acts mainly on presynaptic site and increases the release of chemical transmitter, ATP or prevents the inactivation of ATP. Also, NO may act, at least in part, on postsynaptic site and potentiates the contractile response to ATP in the presence of NA.

Sympathetic neurotransmission in the rat testicular capsule: functional characterization and identification of mRNA encoding alpha1-adrenoceptor subtypes

The rat testicular capsule is a thin tissue surrounding the testis, whose precise function is still unknown. We have studied the contractile effects of electrical field stimulation, noradrenaline, and the blockade by antagonists of adrenergic receptors, in order to characterize sympathetic neurotransmission, and adrenoceptor subtypes. In addition, reverse transcription polymerase chain reaction (RT-PCR) assays were made to check for the expression of the three known subtypes of alpha(1)-adrenoceptors. The effects of electrical field stimulation (2 to 20 Hz, 1 ms, 60 V) were almost totally abolished by depletion of neuronal noradrenaline storage with reserpine (10 mg/Kg), but not by the purinergic receptor antagonist suramin (10(-5) M), indicating that noradrenaline, but not ATP, was involved in contractions. The selective alpha(1)-adrenoceptor antagonist prazosin (10(-7) M) was more effective than the selective alpha(2)-adrenoceptor antagonist idazoxan (10(-7) M) to inhibit contractions induced by electrical field stimulation, pointing out a major involvement of alpha(1)-adrenoceptor. When noradrenaline was used instead of electrical field stimulation, it showed a high potency (pD(2)=7.9). Noradrenaline-induced contractions were competitively blocked by the selective alpha(1A)-adrenoceptor antagonists WB 4101 (pA(2)=8.88), phentolamine (pA(2)=8.39) and by the alpha(1B)-adrenoceptor antagonist spiperone (pA(2)=8.57), indicating the presence of functional alpha(1A)- and alpha(1B)-adrenoceptors. In addition, contractions were not blocked by the selective alpha(1D)-adrenoceptor antagonist BMY 7378 (up to 10(-6) M), while selective alpha(2)-adrenoceptor antagonists showed low pA(2) values (yohimbine, 7.25 and idazoxan, 7.49), suggesting a minor role, if any, for alpha(1D)- and alpha(2)-adrenoceptors. To check the proportionate role of alpha(1A)- and alpha(1B)-adrenoceptors, we blocked alpha(1B)-adrenoceptors with chloroethylclonidine (CEC, 30 microM, 45 min), that reduced the maximal effect of noradrenaline by about 60%. The remnant CEC-insensitive noradrenaline contraction was assumed to be unrelated to alpha(1B)-adrenoceptor, and was inhibited by 5-methyl-urapidil (pA(2)=8.94) and by the Ca(2+) channel blocker nifedipine (3 microM), confirming the involvement of alpha(1A)-adrenoceptors. The presence of mRNA encoding alpha(1A)- and alpha(1B)-adrenoceptor was also shown on RT-PCR assays. Unexpectedly, alpha(1D)-transcripts were also detected in these assays. Taken together, our results show that ATP co-transmission could not be detected, and that neurotransmission involves the interaction of noradrenaline with both alpha(1A)- and alpha(1B)-, but not with alpha(1D)- or alpha(2)-adrenoceptor. The fact that the functional alpha(1D)-adrenoceptor could not be detected in spite of the presence of the corresponding mRNA, remains to be investigated.

L-NAME pre-treatment partially inhibits the agmatine-evoked depression of the electrically induced twitch contraction of isolated rat vas deferens

The effect of the putative endogenous ligand for alpha(2)-adrenoceptors and imidazoline receptors agmatine was studied in sympathetic neurotransmission in the rat epididymal vas deferens. Tissues were obtained from N(varpi)-nitro-l-arginine methyl ester (l-NAME)-treated or normal animals and were contracted by electrical stimulation or by exogenous adenosine 5'-triphosphate (ATP). In the electrically stimulated epididymal end, agmatine produced an inhibitory effect on twitch contraction that was partially reversed in l-NAME-treated animals, whereas the inhibition produced by clonidine was not affected by l-NAME treatment. The nitric oxide (NO)-donor S-nitroso-N-acetyl-penicillamine (SNAP) also inhibited twitch contraction. Neither agmatine nor SNAP interfered with the responses induced by exogenous ATP in the epididymal end. Removal of the epithelium of the preparation did not modify the agmatine response. We conclude that a nitrergic pathway activated by agmatine plays a role in its inhibitory effect in rat vas deferens, but it remains to be investigated whether it results from a direct action on the enzyme NO-synthase or a receptor-mediated mechanism.

Neocuproine, a copper (I) chelator, potentiates purinergic component of vas deferens contractions elicited by electrical field stimulation

Effects of the specific copper (I) chelator, neocuproine, on the purinergic and adrenergic components of nerve-evoked contractions were investigated in the prostatic rat vas deferens. Electrical field stimulation (EFS; 4 Hz) induced bimodal contractions of vas deferens tissue in the presence of alpha1-adrenoceptor antagonist prazosin (to isolate the purinergic component) or purinoceptor antagonist suramin (to isolate the adrenergic component). Neocuproine significantly potentiated the purinergic component of the contractile responses to EFS. However, the same agent failed to elicit any significant effect on the adrenergic component of nerve-evoked contractions. The copper (II) chelator cuprizone could not affect the purinergic component of contractions. The potentiating effect of neocuproine which was reversible after washout of the drug, did not occur following the application of the pre-prepared neocuproine-copper (I) complex. A nitric oxide synthase inhibitor, L-nitroarginine; a cyclooxygenase inhibitor, indomethacin or an alpha2-adrenoceptor antagonist, yohimbine, failed to alter the responses to neocuproine on the purinergic component of the contraction to EFS. Neocuproine did not elicit any significant effect on preparations in which the purinergic receptors were desensitized with alpha,beta-methylene ATP. In conclusion, our results suggest that neocuproine potentiates the purinergic component of rat vas deferens contractions elicited by EFS, presumably by facilitating purinergic neurotransmission and that copper (I)-sensitive mechanisms can modulate purinergic transmission in this tissue.

Enhancement of purinergic neurotransmission by galantamine and other acetylcholinesterase inhibitors in the rat vas deferens

Galantamine, a mild acetylcholinesterase inhibitor and an allosteric ligand of nicotinic receptors, enhanced in a concentration-dependent manner the amplitude of purinergic twitch contractions of the electrically stimulated rat vas deferens (0.2 Hz, 1 ms, 60 V). Other acetylcholinesterase inhibitors also increased the twitches, showing a hierarchy of potencies of galantamine>physostigmine>tacrine>rivastigmine=donepezil. The potentiations seem to be unrelated to the ability to inhibit acetylcholinesterase, since the hierarchy of potencies to block the enzyme in vas deferens was tacrine>physostigmine>rivastigmine>donepezil>galantamine. Acetylcholine also increased the twitches; such effect was produced by a low range of concentrations of acetylcholine (10(-10)-10(-7) M). This facilitatory effect of acetylcholine on twitches was significantly potentiated by galantamine (10(-7)-10(-6) M), but not by rivastigmine or donepezil. A striking enhancement of twitches was also caused by charybdotoxin, a blocker of high-conductance Ca2+-activated K+ channels, and by 4-aminopyridine, a non-specific blocker of K+ channels; in addition, apamin, a blocker of small-conductance Ca2+-activated K+ channels, induced a lower potentiation. The antagonist mecamylamine (10(-7)-10(-6) M) reduced by 80% the potentiation by galantamine, indicating the involvement of nicotinic receptors. Therefore, it is suggested that, besides an inhibition of acetylcholinesterase, some additional mechanisms, such as blockade of Ca2+-dependent K+ channels, or activation of nicotinic receptors of nerve terminals, might be involved in twitch potentiation. These results are relevant in the context of the clinical use of galantamine to improve cognition and behaviour in patients with Alzheimer's disease.

Phenylephrine Induces Endogenous Noradrenaline Release in the Rat Vas deferens through Nitric Oxide Synthase Pathway

We have previously observed that in the rat vas deferens nitric oxide synthase pathway potentiated phenylephrine-induced contractility raising the possibility of a facilitatory role on neurotransmission by nitric oxide. To confirm this hypothesis we studied the effect of phenylephrine on the concentration response curves obtained in preparations from reserpine-treated rats in the absence and presence of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). The endogenous noradrenaline released by normal preparations (without reserpine) was measured in the perfusion fluid of preparations stimulated with phenylephrine, in the absence and presence of L-NMMA, L-NMMA + the nitric oxide donor 3-morpholinosydnonimine hydrochloride (SIN-1), the alpha1-adrenoceptor antagonist prazosin and the blocker of noradrenaline carrier desipramine. The phenylephrine-induced noradrenaline release in a calcium-free medium was also measured. L-NMMA decreased the Emax of phenylephrine concentration response curves obtained in preparations from normal (reserpine-untreated) but not from reserpine-treated rats. In the perfusion fluid of preparations incubated with phenylephrine, a concentration-dependent increase of noradrenaline was observed which was reversed by L-NMMA and restored when SIN-1 was added together with the nitric oxide synthase inhibitor. The concentration-dependent phenylephrine-induced noradrenaline increase was not modified by desipramine but was abolished by 10 microM prazosin. In calcium-free medium, phenylephrine failed to increase the noradrenaline concentration. These results suggest that in the rat vas deferens, nitric oxide pathway potentiates the phenylephrine-induced contractility through a mechanism which involves calcium-dependent release of endogenous noradrenaline and seems to depend, at least partially on the activation of alpha1-adrenoceptors.

Nitric oxide synthase/guanylate cyclase pathway modulates the rat vas deferens contractility induced by phenylephrine

The involvement of the nitric oxide synthase/soluble guanylate cyclase pathway on the modulation of phenylephrine-induced contractility in the rat vas deferens was investigated. Phenlylephrine-concentration response curves were obtained in absence and in presence of inhibitors, N(G)-Nitro-L-arginine (L-NOARG), NG-Nitro-L-arginine methyl esther (L-NAME) or N(G)-monomethyl-L-arginine (L-NMMA) or GC inhibitior, 1H-(1,2,4)-oxadiaziol-(4,3-a)quinoxalin-1-one (ODQ) or nitric oxide donor, 3-morpholinosydnonimine hydrochloride (SIN-1) alone or together with L-NMMA or ODQ. Both nitric oxide synthase and GC inhibitors reduced the Phe-Emax. SIN-1 alone did not change phenylephrine-induced responses and it could reverse the L-NMMA effect but not ODQ effect. The reduction of the phenylephrine-induced contractility obtained in consequence of the inhibition of the nitric oxide/GC pathway suggest that, in the rat vas deferens, despite its well identified relaxant properties, nitric oxide potentiates the contractility induced by adrenergic stimulation.

The effects of sodium nitroprusside on mediator release and the functional properties of postsynaptic membranes in the neuromuscular synapse

Experiments on neuromuscular preparations of frog skin- thoracic muscle and sartorius muscle, using extracellular recording and two-electrode clamping of the muscle fiber membrane potential, were used to study the effects of the nitric oxide donor sodium nitroprusside on endplate currents. At a concentration of 100 microM, sodium nitroprusside sharply decreased the amplitude and quantum composition of the endplate currents, and also decreased the miniature endplate current frequency. The amplitude-time characteristics of miniature endplate currents, the voltage-dependent amplitude, and the decay time constant of miniature endplate currents did not change as compared with controls. However, unlike the situation with other secretion inhibitors, the decrease in endplate current amplitude was not accompanied by increased facilitation in response to rhythmic stimulation or changes in postsynaptic potentiation in conditions of application of pairs of stimuli to muscles. The suppression of acetylcholine secretion was not seen with inactivated sodium nitroprusside solution. These results provide evidence that nitric oxide can be a powerful inhibitor of both spontaneous and evoked transmitter secretion in the neuromuscular synapse, and that this is accompanied by decreases in the efficiency of presynaptic forms of short-term plasticity, while the functional characteristics of the postsynaptic membrane remain unchanged.

Nitric oxide-induced cGMP accumulation in the mouse bladder is not related to smooth muscle relaxation

The functional role of nitric oxide (NO) and the guanylate cyclase/cGMP second messenger system was investigated in the mouse bladder. Electrical field stimulation and the NO-donor 3-morpholino-sydnonimin hydrochloride (SIN-1) did not induce relaxation of the carbachol-precontracted bladder. However, sodium nitroprusside (10(-3) M) was found to enhance the contractile response to electrical field stimulation by 24+/-6% (n=8; P<0.05) without affecting the contractile response to carbachol. The enhancement of bladder contractility evoked by sodium nitroprusside was inhibited by the guanylate cyclase inhibitor 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalime-1-one (ODQ; 10(-6) M). Incubation of bladder strips with SIN-1 and sodium nitroprusside caused an increase in cGMP accumulation as measured by radioimmunoassay. Immunohistochemical studies showed cGMP-immunoreactivity in nerve fibres and in stromal cells, but not in smooth muscle bundles after exposure to NO-donors. The results show that NO-donors have no inhibitory effect on smooth muscle tone in the mouse bladder, but that NO may have a functional role as an excitatory neuromodulator. The targets of endogenous NO in the bladder may be the demonstrated cGMP-positive structures, i.e., nerves and stromal cells.

Colocalisation of neuropeptides, nitric oxide synthase and immunomarkers for catecholamines in nerve fibres of the adult human vas deferens

Single and double-label immunofluorescence methods were used to determine the distribution and patterns of colocalisation of various neuropeptides and nitric oxide synthase (NOS) with the catecholamine synthesising enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DbetaH) in nerve fibres within specimens of adult human vas deferens obtained at vasectomy (age range 28 to 83 y). Cholinergic nerve fibres were immunolabelled with an antiserum to vesicular acetylcholine transporter (VAChT). Using the general nerve marker protein gene product 9.5 (PGP) the density of intramural nerve fibres was found to be similar irrespective of age. Many of these axons, especially in the outer 2 muscle layers were TH and DbetaH-immunoreactive (IR) and were thus confirmed as noradrenergic. Fewer such axons were seen in the inner longitudinal muscle layer. All the noradrenergic nerve fibres also displayed NPY-immunoreactivity with minor populations containing galanin (GAL) or somatostatin (SOM). Nerve fibres lacking TH and DbetaH-IR were immunoreactive for VAChT and were sparsely distributed throughout the 2 outer muscle layers but more numerous in the inner muscle layer. Nerves lacking TH and DbetaH were immunoreactive for NPY and some also contained NOS, VIP or CGRP. These results have been compared with those obtained previously from specimens of human neonatal and infant vas deferens where, in contrast to the present results, NOS and VIP were shown to be colocalised with TH in many of the intramuscular nerve fibres. It thus appears that NOS and VIP cease their coexistence with TH in intramuscular nerve fibres of the human vas deferens between the pre- and postpubertal states. In addition to the intramuscular nerve fibres a VAChT-IR subepithelial nerve plexus occurs in the vas deferens and may control the secretory activity of the lining epithelium. Most of these subepithelial nerve fibres were immunoreactive for NPY and many also contained VIP while minor populations were immunoreactive for NOS, GAL, SOM or SP although fibres containing CGRP were not observed. The neuropeptide content of the subepithelial nerve plexus was similar to that observed in the infant, except for an increased density of VIP-IR nerves, which may reflect greater activity of the lining epithelial cells in the adult vas deferens.

Physiological features of visceral smooth muscle cells, with special reference to receptors and ion channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

Nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in postganglionic parasympathetic nerves innervating the rat vas deferens

Cross-sections of the vas deferens taken from control adult male rats showed positive histochemical reactivity to acetylcholinesterase and immunoreactivity for antibodies to protein gene product 9.5, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, nitric oxide synthase and calcitonin gene-related peptide. Immunoreactivity to substance P was very sparse. Histochemical reactivity to acetylcholinesterase and immunoreactivity to vasoactive intestinal polypeptide and nitric oxide synthase was concentrated in the subepithelial lamina propria and inner smooth muscle layers. Complete surgical denervation resulting from transection of the nerve arising from the pelvic ganglion which supplies the vas deferens totally abolished the immunoreactivity to all of the antibodies tested as well as the histochemical reactivity to acetylcholinesterase. In sections of the prostatic end of the vas deferens taken from rats neonatally pretreated with capsaicin, immunoreactivity to calcitonin gene-related peptide and substance P was reduced by 75 and 83%, respectively. Immunoreactivity to neuropeptide Y, vasoactive intestinal polypeptide and nitric oxide synthase was similar in tissue sections taken from capsaicin-treated rats and those taken from control tissues. Pretreatment of rats with guanethidine or 6-hydroxydopamine decreased immunoreactivity to tyrosine hydroxylase and neuropeptide Y by 60-70%, but immunoreactivity to substance P, vasoactive intestinal polypeptide and nitric oxide synthase was unchanged, while immunoreactivity to calcitonin gene-related peptide and acetylcholinesterase staining was increased by guanethidine but not by 6-hydroxydopamine treatment. Triple labelling experiments showed nitric oxide synthase, vasoactive intestinal polypeptide and acetylcholinesterase all to be co-localized in some nerve fibres. These results indicate that the nitric oxide synthase contained in the nerve fibres innervating the rat vas deferens is unaffected by pretreatment of rats with capsaicin, 6-hydroxydopamine or guanethidine but is abolished by surgical denervation, of postganglionic parasympathetic, sympathetic and sensory nerves. Therefore it appears that nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in the postganglionic parasympathetic nerves which innervate the rat vas deferens.

Nitric oxide as neuromodulator of sympathetic transmission in rat vas deferens

1. Electrical field stimulation (EFS) of muscle strips in vitro elicited a tetrodotoxin (TTX)-sensitive biphasic contractile response consisting of a phasic component followed by a tonic one. 2. The amplitude of both components of the response was impaired by N omega-nitro-L-arginine and potentiated by sodium nitroprusside. Cystamine caused a reduction in amplitude of both phasic and tonic components of the response to EFS. Neither N omega-nitro-L-arginine, sodium nitroprusside, nor cystamine induced changes in the resting muscle tone, or in the contractile response to exogenous agonists ATP and noradrenaline (NA). 3. The nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, induced a reduction in amplitude of both components of the response to EFS. 4. These results reveal a facilitatory prejunctional modulatory role for nitric oxide in sympathetic neurotransmission in rat vas deferens. Endogenous nitric oxide released in the extracellular space is presumed to potentiate neurotransmission by acting at prejunctional level via cGMP.

Sodium nitroprusside enhances contractions of the guinea-pig isolated vas deferens

The effects of sodium nitroprusside on the electrical and mechanical properties of the smooth muscle of the guinea-pig vas deferens, and its responses to transmitter substances, have been investigated by use of the sucrose-gap technique. Isolated longitudinal segments of guinea-pig vas deferens contracted in response to electrical field stimulation (100 V, 0.04-0.1 ms, 1-5 Hz, 10 s train every 60 s) and application of ATP (1 mM) or noradrenaline (10 microM). Sodium nitroprusside (0.1 mM) did not affect resting tension but did enhance contractions evoked by electric-field stimulation but not by ATP or noradrenaline. The sodium nitroprusside-induced enhancement was unaffected by the nitric oxide synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) (0.1 mM). Conversely, electrically evoked contractions were unaffected by the nitric oxide precursor L-arginine (1 mM) or the nitric oxide donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) (0.1 mM). The amplitudes of electrically evoked excitatory junction potentials (EJPs) were not affected by application of sodium nitroprusside, although it caused a small depolarization of 0.7+/-0.3 mV. Similarly, the depolarization caused by exogenous application of ATP or noradrenaline was unaffected by the presence of sodium nitroprusside. L-NAME, L-arginine and SNAP did not affect EJP amplitude or baseline membrane potential. It is concluded that sodium nitroprusside enhances electrically evoked contractions of the guinea-pig vas deferens by reducing the threshold voltage for action potential firing in smooth-muscle cells.

Evidence against nitrergic neuromodulation in the rat vas deferens

Electrical field stimulation (60 V, 1 ms, single pulses or 20 s trains of 1-10 Hz) of the nerve terminals within the rat vas deferens produced biphasic contractions in preparations oriented to measure either longitudinal or circular muscle contractions. In confirmation of earlier reports, these contractions were blocked by tetrodotoxin (1 microM). The initial fast purinergic contraction was dominant in prostatic halves of the vas deferens while the second slower noradrenergic contraction was greater in epididymal halves. Although previous studies have shown nitric oxide synthase immuno-positive nerves in the vas deferens, electrical field stimulation-induced contractions were unaffected by L-arginine, sodium nitroprusside, N-nitro-L-arginine methyl ester (L-NAME) or superoxide dismutase in concentrations up to I mM. In concentrations above 1 mM, L-NAME reduced the size of the field stimulation-induced contractions but this effect could not be reversed by either L-arginine or sodium nitroprusside. Furthermore, L-arginine, sodium nitroprusside and L-NAME did not affect the contractions induced by exogenous application of noradrenaline (10 microM), ATP (1 mM) or BaCl2 (1-10 mM). We conclude that nitric oxide does not act as a neuromodulator in isolated preparations of rat vas deferens.

Mechanism of nitric oxide-induced contraction in the rat isolated small intestine

1. The contractile response to nitric oxide (NO) in ral ileal myenteric plexus-longitudinal muscle strips was pharmacologically analysed. 2. NO (10(-7) M) induced only contraction while 10(-6) M NO induced contraction followed by relaxation. Methylene blue (up to 10(-4) M) did not affect the NO-induced contractions but significantly reduced the relaxation evoked by 10(-6) M NO. Administration of 8-bromo-cyclic GMP (10(-6)-10(-4) M) only induced relaxation. 3. Sodium nitroprusside (SNP; 10(-7)-10(-5) M) induced concentration-dependent contractions per se; the contractile response to NO, administered within 10 min after SNP, was concentration-dependently reduced. The guanosine 3':5'-cyclic monophosphate (cyclic GMP) content of the tissues was not increased during contractions with 10(-8) M NO and 10(-6) M SNP; it was increased by a factor of 2 during contraction with 10(-7) M NO, and by a factor of 12 during relaxation with 3 x 10(-6) M NO. 4. The NO-induced contractions were not affected by ryanodine (3 x 10(-5) M) but were concentration-dependently reduced by nifedipine (10(-8)-10(-7) M) and apamin (3 x 10(-9)-3 x 10(-8) M). 5. These results suggest that cyclic GMP is not involved in the NO-induced contraction in the rat small intestine. The NO-induced contraction is related to extracellular Ca2+ influx through L-type Ca2+ channels, that might be activated in response to the closure of Ca(2+)-dependent K+ channels.

Functional properties of agmatine in rat vas deferens

Experiments were performed with rat vas deferens to verify whether agmatine, an endogenous ligand for adrenoceptors and imidazoline receptors, can influence sympathetic neurotransmission, with respect to contractions induced by transmural nerve stimulation, contractions induced by exogenous noradrenaline, and overflow of endogenous noradrenaline. It was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls, (b) shifted to the right the inhibitory concentration-response curves for clonidine on electrically induced twitches, indicating competitive antagonism at presynaptic alpha-adrenoceptors, with a pA2 value of 4.12 +/- 0.10, (c) shifted to the right the concentration-response curves for noradrenaline-induced contractions, indicating competitive antagonism at postsynaptic alpha-adrenoceptors as well, with a pA2 value of 4.03 +/- 0.10, and (d) caused a dose-dependent increase of KCI-induced overflow of noradrenaline, up to about 90% in relation to controls. It is concluded that agmatine has multiple effects on sympathetic neurotransmission in rat vas deferens.