Feedback via Ca²⁺-activated ion channels modulates endothelin 1 signaling in retinal arteriolar smooth muscle

PURPOSE: To investigate the role of feedback by Ca²?-sensitive plasma-membrane ion channels in endothelin 1 (Et1) signaling in vitro and in vivo. Methods. Et1 responses were imaged from Fluo-4-loaded smooth muscle in isolated segments of rat retinal arteriole using two-dimensional (2-D) confocal laser microscopy. Vasoconstrictor responses to intravitreal injections of Et1 were recorded in the absence and presence of appropriate ion channel blockers using fluorescein angiograms imaged using a confocal scanning laser ophthalmoscope. Results. Et1 (10 nM) increased both basal [Ca²?](i) and the amplitude and frequency of Ca²?-waves in retinal arterioles. The Ca²?-activated Cl?-channel blockers DIDS and 9-anthracene carboxylic acid (9AC) blocked Et1-induced increases in wave frequency, and 9AC also inhibited the increase in amplitude. Iberiotoxin, an inhibitor of large conductance (BK) Ca²?-activated K?-channels, increased wave amplitude in the presence of Et1 but had no effect on frequency. None of these drugs affected basal [Ca²?](i). The voltage-operated Ca²?-channel inhibitor nimodipine inhibited wave frequency and amplitude and also lowered basal [Ca²?](i) in the presence of Et1. Intravitreal injection of Et1 caused retinal arteriolar vasoconstriction. This was inhibited by DIDS but not by iberiotoxin or penitrem A, another BK-channel inhibitor. Conclusions. Et1 evokes increases in the frequency of arteriolar Ca²?-waves in vitro, resulting in vasoconstriction in vivo. These responses, initiated by release of stored Ca²?, also require positive feedback via Ca²?-activated Cl?-channels and L-type Ca²?-channels.

DETECTION OF CLENBUTEROL RESIDUES IN BOVINE LIVER, MUSCLE, RETINA AND URINE USING GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A gas chromatographic/mass spectrometric method is described for the detection of clenbuterol residues in liver, muscle, urine and retina. Tissue samples are first digested using protease and any clenbuterol present is extracted using a simple liquid/liquid extraction procedure. The dried extracts are then derivatized using methylboronic acid and the derivatives are subjected to gas chromatography/mass spectrometry on a magnetic sector instrument. The detection limit of the assay is 0.05 ng g-1 clenbuterol in liver, muscle or urine using a 10 g sample size, and 4 ng g-1 in retina using a 0.5 g sample size. The assay is made very specific by using selected ion monitoring of three ions at a resolution of 3500 and by ion ratio measurements. The precision and reproducibility of the assay are enhanced by the use of a deuterated internal standard, with a typical coefficient of variation of 3%.

THE ACTION OF SEROTONIN AND THE NEMATODE NEUROPEPTIDE KSAYMRFAMIDE ON THE PHARYNGEAL MUSCLE OF THE PARASITIC NEMATODE, ASCARIS-SUUM

The pharyngeal component of the enteric nervous system of the parasitic nematode, Ascaris suum exhibits immunoreactivity for serotonin (5-hydroxytryptamine or 5-HT) and for FMRFamide-like peptides. This paper describes the application of an in vitro pharmacological approach to investigate the functional role of 5-HT and FMRFamide-like peptides. The pharyngeal pumping behaviour of Ascaris suum was monitored using a modified pressure transducer system which measures pharyngeal pressure changes and therefore pumping. The pharynx did not contract spontaneously; however, 5-HT (10-1000 mu M) stimulated pumping at a frequency of 0 . 5 Hz. FMRFamide had no apparent effect on pharyngeal pumping. The native nematode FMRFamide-related peptide (FaRP), KSAYMRFamide inhibited the pumping elicited by 5-HT. The duration of inhibition was dose-dependent (0 . 1-1000 nM) with a threshold of 0 . 1 nM. In 4 preparations, the inhibition of the pharyngeal muscle was preceded by an initial excitation and increase in the amplitude of pharyngeal pressure changes. The pharynx is involved in various nematode processes, including feeding, regulation of hydrostatic pressure and excretion. The role of 5-HT and KSAYMRFamide in the pharyngeal function of nematodes is discussed.

Gross anatomy of the muscle systems of Fasciola hepatica as visualized by phalloidin-fluorescence and confocal microscopy

Neuropeptides, biogenic amines and acetylcholine are expressed abundantly within the nervous systems of parasitic flatworms, and are particularly evident in the innervation of the musculature. Such associations have implicated the nervous system in locomotion, host attachment and reproductive co-ordination. Information on the muscle systems of parasitic flatworms is generally sparse, in particular those muscles associated with the reproductive system, intestinal tract and attachment apparatus. Also, the use of sectioned material has left description of the 3-dimensional organization of the musculature largely unrecorded. Using fluorescein isothiocyanate (FITC)-labelled phalloidin as a site-specific probe for filamentous actin, applied to whole-mount preparations of adult Fasciola hepatica and examined by confocal scanning laser microscopy, the present work reports on the organization of the major muscle systems in this trematode parasite. A highly regular array of outer circular, intermediate longitudinal and inner diagonal fibres distinguishes the body wall musculature, which is also involved in the development of both ventral and oral suckers. Circular fibres dominate the duct walls of the male and female reproductive systems, whereas the muscles of the intestinal tract have a somewhat diffuse arrangement of fibres. An understanding of the structural complexity of the muscle systems of parasitic flatworms is considered as fundamental to the interpretation of results from physiological experiments.

Structure-activity relationships of FMRFamide-related peptides contracting Schistosoma mansoni muscle

This study reports the potent myoactivity of flatworm FMRFamide-related peptides (FaRPs) on isolated muscle fibers of the human blood fluke, Schistosoma mansoni. The turbellarian peptides YIRFamide (EC50 4 eta M), GYIRFamide (EC50 1 eta M). and RYIRFamide (EC50 7 eta M), all induced muscle contraction more potently than the cestode FaRP GNFFRFamide (EC50 500 eta M). Using a series of synthetic analogs of the flatworm peptides YIRFamide, GYIRFamide and RYIRFamide, the structure-activity relationships of the muscle FaRP receptor were examined. With a few exceptions, each residue in YIRFamide is important in the maintenance of its myoactivity. Alanine scans resulted in peptides that were inactive (Ala(1), Ala(2), Ala(3) and Ala(4) YIRFamide; Ala(4) and Ala(5) RYIRFamide) or had much reduced potencies (Ala(1), Ala(2) and Ala(3) RYIRFamide). Substitution of the N-terminal (Tyr(1)) residue of YIRFamide with the non-aromatic residues Thr or Arg produced analogs with greatly reduced potency. Replacement of the N-terminal Tyr with aromatic amino acids resulted in myoactive peptides (FIRFamide, EC50 100 eta M; WIRFamide, EC50 0.5 eta M). The activity of YIRFamide analogs which possessed a Leu(2), Phe(2) or Met(2) residue (EC50's 10, 1 and 3 eta M, respectively) instead of Ile(2) was not significantly altered, whereas, YVRFamide had a greatly reduced (EC50 200 eta M) activity. Replacement of the Phe(4) with a Tyr(4) (YIRYamide) also greatly lowered potency. Truncated analogs were either inactive (FRFamide, YRFamide, HRFamide, RFamide, Famide) or had very low potency (IRFamide and MRFamide), with the exception of nLRFamide (EC50 20 eta M). YIRF free acid was inactive. In summary, these data show the general structural requirements of this schistosome muscle FaRP receptor to be similar, but not identical, to those of previously characterized molluscan FaRP receptors. (C) 1997 Elsevier Science Inc.

Pharmacological effects of nematode FMRFamide-related peptides (FaRPs) on muscle contractility of the trematode, Fasciola hepatica

The physiological effects of synthetic replicates of the nematode FaRPs, AF1 (KNEFIRFamide), AF2 (KHEYLRFamide), PF1 (SDPNFLRFamide), PF2 (SADPNFLRFamide), AF8/PF3 (KSAYMRFamide) and PF4 (KPNFIRFamide) were examined on muscle preparations of the liver fluke, Fasciola hepatica. Changes in contractility following the addition of the test compound were recorded using a photo-optic transducer system. Unlike the varied effects these peptides have on nematode somatic musculature, all were found to induce excitatory responses in the muscle activity of F. hepatica. While qualitative effects of the nematode peptides were similar in that they induced increases in both the amplitude and frequency of F. hepatica muscle contractions, they varied considerably in the potency of their excitatory effects. The threshold activity for each peptide was as follows: 10 mu M, PF1 and PF2; 3 mu M, AF1 and PF3; 1 mu M, AF2; and 30 nM, PF4. The results demonstrate, for the first time, the cross-phyla activity of nematode neuropeptides on the neuromuscular activity of a trematode.

Physiological effects of platyhelminth RFamide peptides on muscle-strip preparations of Fasciola hepatica (Trematoda: Digenea)

The effects of each of the known platyhelminth neuropeptides were determined on muscle-strip preparations from the liver fluke, Fasciola hepatica. The activity of synthetic replicates of the C-terminal nonapeptide of neuropeptide F (NPF9, Moniezia expansa), and the FMRFamide-related peptides (FaRPs), GNFFRFamide, RYIRFamide, GYIRFamide and YIRFamide, were examined. Muscle-strip activity was recorded from 1 mm segments of muscle prepared from 28 to 32-day-old worms, using a photo-optic transducer system. None of the peptides (less than or equal to 10 mu M) altered baseline tension significantly; however, each of the peptides increased the amplitude and frequency of muscle contraction. The threshold for activity of each of the peptides examined was, respectively, 1 nM (RYIRFamide), 0.3 mu M (GYIRFamide and YIRFamide), and 10 mu M (GNFFRFamide and NPF9). All of the effects were reversible and repeatable, following wash-out. Muscle-strip integrity was tested following experimentation, using arecoline (10 mu M) and high-K+ bathing medium (90 mM K+).

ISOLATION AND PRELIMINARY BIOLOGICAL CHARACTERIZATION OF KPNFIRFAMIDE, A NOVEL FMRFAMIDE-RELATED PEPTIDE FROM THE FREE-LIVING NEMATODE, PANAGRELLUS-REDIVIVUS

A novel FMRFamide-related heptapeptide, Lys-Pro-Asn-Phe-Ile-Arg-Phe-NH2 (KPNFIRFamide), was isolated and characterized from acid ethanol extracts of the free-living nematode, Panagrellus redivivus. Whole-worm extracts contained greater than or equal to 9 pmol KPNFIRFamide/g wet weight. A synthetic replicate of this peptide induced a rapid relaxation of tone and inhibited spontaneous contractility in isolated innervated and denervated body-wall muscle strips of the parasitic nematode, Ascaris suum. KPNFIRFamide (0.1 nM) induced measurable relaxations in 50% of the muscle preparations examined. Concentrations greater than or equal to 0.3 nM induced relaxation in 100% of muscle preparations examined. The relaxation was short-lived at concentrations of peptide greater than or equal to 1 mu M and displayed a profile typical of receptor desensitization. These data suggest the occurrence of a closely related peptide in A. suum and add further evidence to the concept of primary structural conservation of FaRPs within the nematodes.

PLATYHELMINTH FMRFAMIDE-RELATED PEPTIDES (FARPS) CONTRACT SCHISTOSOMA-MANSONI (TREMATODA, DIGENEA) MUSCLE-FIBERS IN-VITRO

Molluscan FMRFamide and two recently discovered platyhelminth FMRFamide-related peptides (FaRPs), GNFFRFamide from the cestode Moniezia expansa and RYIRFamide from the terrestrial turbellarian Artioposthia triangulata, cause dose-dependent contractions of individual muscle fibres from Schistosoma mansoni in vitro. The most potent FaRP tested was the turbellarian peptide RYIRFamide, which produced a concentration-dependent effect between 10(-9) and 10(-7) M. FMRFamide and GNFFRFamide were less potent, inducing contractions between 10(-8)-10(-6) M and 10(-7)-10(-5) M respectively. The contractile effect of each of these peptides was blocked by the presence of 1 mu M FMR-D-Famide. FMRF free acid did not elicit contraction of the muscle fibres. The FaRP-induced contractions did not occur if the Ca2+ was omitted and 0.5 mu M EGTA. was added to the extracellular medium. The FaRP-induced contractions were not blocked by the Ca2+ channel blockers nicardipine, verapamil or diltiazem, although high Kf-induced contractions of these fibres were blocked by nicardipine. These data indicate the presence of FaRP receptors on schistosome muscle fibres and demonstrate their ability to mediate muscle contraction. The action of these endogenous flatworm peptides on schistosome muscle is the first demonstration of a direct excitatory effect of any putative neurotransmitter on the muscle of a flatworm, and establishes a role for FaRPs in neuromuscular transmission in trematodes. In addition, it provides the first evidence that the peptidergic nervous system is a rational target for chemotherapeutic attack in parasitic platyhelmiths.

Glucose-induced oxidative stress in vascular contractile cells - Comparison of aortic smooth muscle cells and retinal pericytes

Free radical-mediated damage to vascular cells may be involved in the pathogenesis of diabetic vasculopathy. The aim of this study was to compare the extent of glucose-induced oxidative stress in both vascular smooth muscle cells (VSMCs) and pericytes and the effect on antioxidant enzyme gene expression and activities. Porcine aortic VSMC and retinal pericytes were cultured in either 5 or 25 mmol/l glucose for 10 days. Intracellular malondialdehyde (MDA) was measured as a marker of peroxidative damage, and mRNA expression of CuZn-SOD, MnSOD, catalase, and glutathione peroxidase (GPX) were measured by Northern analysis. Glutathione (GSH) was also measured. There was a significant increase in MDA in VSMCs in 25 mmol/l glucose (1.34 +/- 0.11 vs. 1.88 +/- 0.24 nmol/mg protein, 5 vs. 25 mmol/l D-glucose, mean +/- SE, n = 15, P