The physiology and pharmacology of neuromuscular transmission in the nematode parasite,Ascaris suum
| Autor: | S. J. Robertson, A. H. Duittoz, A. J. Pennington, Richard J. Martin, John R. Kusel |
|---|---|
| Přispěvatelé: | Department of Preclinical Veterinary Sciences, University of Edinburgh-Royal (Dick) School of Veterinary Studies, University of Glasgow |
| Rok vydání: | 1991 |
| Předmět: |
Male
MESH: Ascaris MESH: Muscle Contraction [SDV]Life Sciences [q-bio] Neuromuscular transmission MESH: gamma-Aminobutyric Acid Synaptic Transmission MESH: GABA Antagonists GABA Antagonists MESH: Structure-Activity Relationship 0302 clinical medicine Receptors Cholinergic MESH: Animals MESH: Parasympatholytics MESH: Receptors GABA-A gamma-Aminobutyric Acid Anthelmintics Motor Neurons 0303 health sciences MESH: Electrophysiology GABAA receptor Ascaris Hyperpolarization (biology) Electrophysiology MESH: Anthelmintics Infectious Diseases medicine.anatomical_structure Parasympathomimetics Excitatory postsynaptic potential Female [SDV.NEU]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC] Ion Channel Gating Locomotion MESH: Motor Neurons Acetylcholine Muscle Contraction medicine.drug medicine.medical_specialty Neuromuscular Junction MESH: Locomotion MESH: Parasympathomimetics Biology Neuromuscular junction Structure-Activity Relationship 03 medical and health sciences Internal medicine MESH: Synaptic Transmission medicine Animals 030304 developmental biology MESH: Receptors Cholinergic [SDV.BA.MVSA]Life Sciences [q-bio]/Animal biology/Veterinary medicine and animal Health MESH: Acetylcholine Parasympatholytics [SDV.BDLR]Life Sciences [q-bio]/Reproductive Biology MESH: Ion Channel Gating GABA receptor antagonist Bicuculline Receptors GABA-A MESH: Male Endocrinology Biophysics Animal Science and Zoology Parasitology MESH: Neuromuscular Junction MESH: Female 030217 neurology & neurosurgery |
| Zdroj: | Parasitology Parasitology, Cambridge University Press (CUP), 1991, 102 (S1), pp.S41-S58. ⟨10.1017/s0031182000073285⟩ |
| ISSN: | 1469-8161 0031-1820 |
| DOI: | 10.1017/s0031182000073285 |
| Popis: | The organization ofAscarismotoneurones and nervous system is summarized. There is an anterior nerve ring and associated ganglia, main dorsal and ventral nerve cords which run longitudinally, and a small set of posterior ganglia. Cell bodies of motoneurones are found in the ventral nerve cord and occur in 5 repeating ‘segments’; each contains 11 motoneurones. Seven morphological types of excitatory or inhibitory motoneurone are recognized.EachAscarissomatic muscle cell is composed of the contractile spindle; the bag region, containing the nucleus; the arm; and the syncytial region, the location of neuromuscular junctions. The resting membrane potential of muscle is approximately — 30 mV and shows regular depolarizing, Ca-dependent ‘spike potentials’ superimposed on smaller Na+- and Ca2+-dependent ‘slow waves’ and even slower ‘modulation waves’. The membrane shows high Cl-permeability. Adjacent cells are electrically coupled so that electrical activity in the cells is synchronized. Acetylcholine (ACh) and γ-aminobutyric acid (GABA) affect the electrical activity. Bath-applied ACh increases membrane cation conductance, depolarizes the cells, alters the frequency and amplitude of spike potentials and produces contraction. Bath-applied GABA increases Cl-conductance, decreases spike activity and causes hyperpolarization and muscle relaxation.The extra-synaptic ACh receptors on the bag region ofAscarismuscle can be regarded as a separate subtype of nicotinic receptor. ACh and anthelmintic agonists (pyrantel, morantel, levamisole) produce a dose-dependent increase in cation conductance and membrane depolarization which is blocked by tubocurarine, mecamylamine but not by hexamethonium. The potency, of GABA agonists, with the exception of sulphonic acid derivatives, correlates with the vertebrate GABAareceptor. The potency of antagonists does not. Thus, bicuculline, securinine, pitrazepine, SR95531 and RU5135 are potent vertebrate GABAaantagonists but have little effect on GABA receptors. The potency order of the arylaminopyridazine GABA antagonists: SR95103, SR95132, SR42666, SR95133, SR95531, SR42627 and SR42640 at theAscarisGABA receptors contrasts with that at vertebrate GABAareceptors. It has been suggested that the receptor is referred to as a GABAnreceptor.Patch-clamp studies show that ACh activates a non-selective cation channel which has a main conductance of 40–50pS and apparent mean open time of 1·3 ms; a smaller channel of 20–30 pS with a similar open-time is also activated. Pyrantel and levamisole also produce openings with similar conductances and open-times. GABA activates a Cl-channel with a main state conductance of 22 pS and an apparent mean open duration of 32 ms; conductance states of 10 and 15 pS are also seen. Piperazine similarly activates this channel but the mean open-time is shorter (14 ms). Ivermectin in high doses, is an antagonist which reduces the GABA channel conductance and Popen; it does, however, open ‘small’ Cl-channels when applied to the outside surface of membrane. These channels have a conductance of 9–15 pS and very long open times (> 100 mS). 5-HT does not have a direct effect on membrane potential or conductance but acts on cAMP levels and glycogen metabolism. Dopamine, octopamine and AF1 may act as neurotransmitters or neuromodulators. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|