Parasympathetic denervation supersensitivity in the rat iris sphincter muscle: an in vitro study

Loss of nitrergic neurotransmission to mouse corpus cavernosum in the absence of neurturin is accompanied by increased response to acetylcholine

The neurotrophic factor, neurturin (NTN), plays an important role in parasympathetic neural development. In the penis, parasympathetic nitrergic/cholinergic nerves mediate the erectile response. However, despite reduced parasympathetic penile innervation in mice lacking the NTN receptor, glial cell line-derived neurotrophic factor family receptor alpha (GFRalpha)2, they are capable of erection and reproduction. Our aim was to assess neural regulation of erectile tissues from mice lacking NTN. Responses of cavernosal smooth muscle were studied in vitro, monitoring agonist- and nerve-evoked changes in tension. Frequency-dependent nerve-evoked relaxations in the presence of guanethidine were markedly reduced in the mutant mice compared to wild types (19 vs 72% of phenylephrine pre-contraction). Atropine reduced the amplitude in wild-type mice to 61%, but abolished relaxations in knockout mice. In wild-type and knockout animals, nitric oxide synthase inhibition abolished neurogenic relaxations. In NTN knockout animals, EC(50) values for nitric oxide-dependent relaxations to acetylcholine and muscarine were increased approximately 0.5 log units. In contrast, contractions to electrical stimulation or phenylephrine, and relaxations to bradykinin or the nitric oxide donor, sodium nitroprusside, were unaltered. Immunohistochemistry confirmed that nerves immunoreactive for nitric oxide synthase, vesicular acetylcholine transporter and vasoactive intestinal polypeptide were substantially reduced in cavernosum of NTN knockout mice. Parallel immunohistochemical and pharmacological studies in GFRalpha2 knockout animals showed the same changes from their wild types as the NTN knockout animals. The data demonstrate that NTN is essential for normal development of penile erection-inducing nerves and that its absence leads to increased responsiveness to muscarinic agonists, possibly as a compensatory mechanism.

Action of biologically active peptides on monkey iris sphincter and dilator muscles

Biologically active peptides modulate pupillary responsiveness in many non-primate mammals. We examined the action of seven different peptides on iris sphincter and dilator muscles of rhesus monkey. Iris sphincter and dilator muscle preparations from rhesus monkeys were mounted in an organ bath, and tension changes were recorded by an isometric transducer. Electrical field stimulation (100Hz, 0.3 msec, 10V) was applied through a pair of platinum plate electrodes. Monkey iris sphincter and dilator muscles produced simple cholinergic and adrenergic excitatory responses respectively to electrical field stimulation. Strong field stimulation did not elicit slow Substance P (SP) mediated contractions like those in rabbit iris sphincter. Exogenously applied pituitary adenylate cyclase-activating peptide (PACAP) enhanced in a concentration-dependent manner (0.3 nM-0.1 microm) the sphincter response to field stimulation, while neuropeptide Y (NPY) and somatostatin (SRIF) attenuated it. These three peptides did not affect sphincter contractions induced by acetylcholine, and therefore were acting at presynaptically. SP, calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin (GAL) had no effect (at 0.1 microm) on iris sphincter. None of seven exogenously applied peptides had an effect on monkey iris dilator muscle. The innervation of primate irises may be relatively simple compared to non-primates because each of the peptides in this study can modulate miosis or mydriasis in non-primate mammals. Future studies will be expected on the functional significance of species differences in iridial innervation.

Molecular analysis of non-specific supersensitivity induced by AF64A in rat iris smooth muscle

Characteristics of supersensitivity induced by the pretreatment with AF64A, an inhibitor of choline uptake at parasympathetic nerve endings, were examined in rat iris sphincter. In preparations isolated and skinned by beta-escin after the micro injection of AF64A to eyes in vivo, the amplitude of maximum contraction in pCa 4.5 solution was increased by 180% of the control from the contralateral eyes. The Ca2+ sensitivity of the contractile system was slightly but significantly increased by AF64A injection; the half maximum contraction was obtained at pCa 5.87 and 6.05 in the control and AF64A-injected eyes, respectively. The increase in maximum contraction in AF64A injected ones was neither affected by the addition of calmodulin, GTPgammaS nor H-7. The increase in Ca2+ sensitivity by AF64A injection was not affected by calmodulin, enhanced by GTPgammaS and abolished by H-7. AF64A injection increased the total protein content only by 30% of the control. The contents of contractile proteins per iris were quantified using Western blotting with monoclonal antibodies. The contents of actin and calponin were increased by AF64A, whereas those of myosin, calmodulin and caldesmon were not affected. The results indicate that AF64A-induced enhancement of the maximum contraction is not mainly due to the increase in the contents of major contractile proteins and that the increase in Ca2+ sensitivity could be due to the mechanism in which changes in protein kinase C and/or GTP binding protein activity are involved.

Ca2+ signaling by cholinergic and alpha1-adrenergic agonists is up-regulated in lacrimal and submandibular glands in a murine model of Sjögren's syndrome

Innervation of the lacrimal gland of MRL/Mp-Fas-lpr/lpr (MRL/lpr), a murine model for Sjögren's syndrome, is unaltered with the onset or progression of the lymphocytic infiltration. To determine whether lacrimal and submandibular gland cells are able to respond to external stimuli, acini were prepared from MRL/lpr (diseased) and MRL/Mp-+/+ (MRL/+, control) mice at 4, 8, and 12 weeks of age and loaded with the fluorescent dye fura-2 to monitor changes in the intracellular Ca2+ concentration ([Ca2+]i) in response to cholinergic and alpha1-adrenergic stimulation, two major stimuli of lacrimal gland protein secretion. Cholinergic-induced [Ca2+]i increase was up-regulated 3- and 4-fold in lacrimal gland acini isolated from 8- and 12-week-old MRL/lpr mice, respectively, compared to 4-week-old animals, but was not up-regulated in age-matched MRL/+ control mice. Similarly, alpha1-adrenergic-induced [Ca2+]i increase was up-regulated 7- and 12-fold in acini isolated from 8- and 12-week-old MRL/lpr mice, respectively, compared to 4-week-old animals, but was not up-regulated in MRL/+ mice. Cholinergic-induced [Ca2+]i increase in submandibular gland acini of MRL/lpr and MRL/+ mice was the same at all ages. In contrast, alpha1-adrenergic-induced [Ca2+]i increase was up-regulated 3-fold in acini from 12-week-old MRL/lpr mice, compared to 4-week-old mice, but was not up-regulated in age-matched MRL/+ mice. We conclude that the Ca2+ signaling portion of cholinergic and alpha1-adrenergic pathway in the lacrimal gland and the Ca2+ signaling portion of alpha1-adrenergic pathway in the submandibular gland is up-regulated with the onset and progression of the lymphocytic infiltration in the MRL/lpr murine model of Sjögren's syndrome.

Effects of surgical sympathetic denervation on G-protein levels, alpha and beta-adrenergic receptors, cAMP production and adenylate cyclase activity in the smooth muscles of rabbit iris

The relative densities of a number of G protein subunits were quantified in membranes prepared from iris sphincter and dilator muscles of rabbits that have undergone sympathetic denervation and from contralateral innervated controls by immunoblotting with specific polyclonal antibodies against Gs alpha, Gi alpha and Gq alpha protein subunits. In addition, alpha and beta-adrenergic receptor densities, basal and isoproterenol (ISO)-stimulated cAMP production, and basal and ISO+GTP gamma S-stimulated adenylate cyclase (AC) activities were measured in the same tissues. Densitometric analysis of the immunoblot data revealed a 32% reduction in the level of Gi alpha in the denervated sphincter, a 26% increase in the level of Gi alpha in the denervated dilator, and no changes due to denervation were found in the levels of Gs alpha and Gq alpha. Sympathetic denervation had no effect on the densities of alpha- and beta-adrenergic receptors in these tissues, however, it did induce a significant decrease in the KD values of alpha-adrenergic receptors in both dilator and sphincter, and in beta-adrenergic receptors in the sphincter. The basal- and ISO-stimulated cAMP production in the sphincter was 4-fold as high as that of the dilator, and at 0.05 microM ISO the denervation supersensitivity for cAMP production in the sphincter increased by 118% as compared to 36% in the dilator. Sympathetic denervation increased by 19-47% the basal- and ISO-stimulated activity of AC in these tissues, however, it had no effect on the phospholipase C activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of muscarinic receptors mediating relaxation and contraction in the rat iris dilator muscle

1. The characteristics of muscarinic receptors mediating relaxation and/or contraction in the rat iris dilator muscle were examined. 2. Relaxation was induced in a dilator muscle by application of acetylcholine (ACh) at low doses (3 microM or less) and contraction was induced by high doses. Methacholine and carbachol also showed biphasic effects similar to those of ACh; in contrast, bethanechol, arecoline, pilocarpine and McN-A-343 induced mainly relaxation but no substantial contraction. 3. After parasympathetic denervation by ciliary ganglionectomy, the relaxant response to muscarinic agonists disappeared upon nerve stimulation. Application of McN-A-343 and pilocarpine induced only small contractions in denervated dilator muscles, indicating that these are partial agonists for contraction. 4. pA2 values of pirenzepine, methoctramine, AF-DX 116, himbacine, and 4-DAMP for antagonism to pilocarpine-induced relaxation in normal dilator muscles and those for antagonism to ACh-induced contraction in denervated dilator muscles were determined. The pA2 values for antagonism to relaxation of all these antagonists were most similar to those for M3-type muscarinic receptors. 5. Although pA2 values for contraction of these antagonists, except for methoctramine, were very close to those for relaxation, contraction was not significantly antagonized by methoctramine. Contraction might be mediated by M3-like receptors which have a very low affinity for methoctramine. 6. In conclusion, ACh-induced biphasic responses in rat iris dilator muscles were clearly distinguished from each other by specific muscarinic agonists and parasympathetic denervation, whereas muscarinic receptors could not be subclassified according to the pA2 values of 5 specific antagonists only.

Pertussis toxin-sensitive muscarinic relaxation in the rat iris dilator muscle

1. The effects of pertussis toxin (PTX) on contraction and/or relaxation induced by agonists or transmural nerve stimulation (TNS) were examined in the rat iris dilator and sphincter muscles. 2. TNS in the presence of phentolamine induced an atropine-sensitive biphasic response: initial contraction followed by relaxation in dilator muscles. Exogenously applied acetylcholine (ACh) elicited a large relaxation at low doses (3 microM or less) and a concentration at high doses. 3. Only the ACh-induced relaxation was affected by injection of PTX (10 ng) into the anterior eye chamber. Relaxation was decreased 12 h after injection and had completely disappeared after 24 h. Relaxation recovered in part 3 weeks and almost completely 8 weeks after PTX treatment. A gradual decrease in muscarinic relaxation in a dilator muscle was also observed in vitro after addition of PTX to the bathing solution. 4. The pA2 values of muscarinic blockers, pirenzepine, AF-DX 116, 4-DAMP, and himbacine for competitive antagonism to ACh-induced contraction were 7.14, 6.53, 9.03, and 6.80, respectively, in PTX-pretreated dilator muscles. These values are comparable to those obtained in parasympathectomized dilator muscles and may indicate involvement of M3 or M3-like receptors in muscle contraction. 5. Pretreatment with PTX did not significantly affect contraction induced by noradrenaline or 5-hydroxytryptamine or the relaxation induced by isoprenaline in dilator muscles. 6. In conclusion, among several agonist-induced responses in the rat iris dilator and sphincter muscles, only muscarinic relaxation in dilator muscle occurs via activation of PTX-sensitive GTP binding proteins.

Parasympathetic denervation abolishes acetylcholine-induced relaxation in the rat iris dilator

An anomalous change in response to exogenously applied acetylcholine (ACh) was found in the rat iris dilator muscle after surgical parasympathetic denervation. The relaxation induced by nerve stimulation in the normal dilator muscles disappeared after the denervation. ACh elicited relaxation and contraction at low (less than 3 X 10(-6) M) and higher doses, respectively, in the normal muscles. The relaxing response to ACh was almost abolished after the denervation, while the maximum contractile response to ACh was not affected significantly.

Mechanism of action of nicotine in isolated iris sphincter preparations of rabbit

1. Nicotine produced a transient contraction of rabbit isolated iris sphincter muscle, a parasympathetic ganglion-free tissue. The response to nicotine was antagonized by hexamethonium, but was insensitive to tetrodotoxin (TTX). While single treatments with atropine, capsaicin or [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-substance P (rpwwL-SP) partially blocked the response, combined treatment abolished it. 2. Chronic treatment of animals with nicotine added to the drinking water (about 12 mg kg-1 per day) had no effect on the responsiveness to nicotine or the pharmacological properties of nicotine-induced contraction. 3. These results suggest that acetylcholine and tachykinin(s) released via sodium channel-independent mechanisms from nerve terminals of parasympathetic and primary sensory nerves, respectively, are involved in the nicotine-induced contractile response.