|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Journal of Experimental Biology, Vol 204, Issue 5 875-885, Copyright © 2001 by Company of Biologists
JOURNAL ARTICLES |
MR Elphick and R Melarange
School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK. M.R.Elphick@qmw.ac.uk
Smooth muscle relaxation in vertebrates is regulated by a variety of neuronal signalling molecules, including neuropeptides and nitric oxide (NO). The physiology of muscle relaxation in echinoderms is of particular interest because these animals are evolutionarily more closely related to the vertebrates than to the majority of invertebrate phyla. However, whilst in vertebrates there is a clear structural and functional distinction between visceral smooth muscle and skeletal striated muscle, this does not apply to echinoderms, in which the majority of muscles, whether associated with the body wall skeleton and its appendages or with visceral organs, are made up of non-striated fibres. The mechanisms by which the nervous system controls muscle relaxation in echinoderms were, until recently, unknown. Using the cardiac stomach of the starfish Asterias rubens as a model, it has been established that the NO-cGMP signalling pathway mediates relaxation. NO also causes relaxation of sea urchin tube feet, and NO may therefore function as a 'universal' muscle relaxant in echinoderms. The first neuropeptides to be identified in echinoderms were two related peptides isolated from Asterias rubens known as SALMFamide-1 (S1) and SALMFamide-2 (S2). Both S1 and S2 cause relaxation of the starfish cardiac stomach, but with S2 being approximately ten times more potent than S1. SALMFamide neuropeptides have also been isolated from sea cucumbers, in which they cause relaxation of both gut and body wall muscle. Therefore, like NO, SALMFamides may also function as 'universal' muscle relaxants in echinoderms. The mechanisms by which SALMFamides cause relaxation of echinoderm muscle are not known, but several candidate signal transduction pathways are discussed here. The SALMFamides do not, however, appear to act by promoting release of NO, and muscle relaxation in echinoderms is therefore probably regulated by at least two neuronal signalling systems acting in parallel. Recently, other neuropeptides that influence muscle tone have been isolated from the sea cucumber Stichopus japonicus using body wall muscle as a bioassay, but at present SALMFamide peptides are the only ones that have been found to have a direct relaxing action on echinoderm muscle. One of the Stichopus japonicus peptides (holothurin 1), however, causes a reduction in the magnitude of electrically evoked muscle contraction in Stichopus japonicus and also causes 'softening' of the body wall dermis, a 'mutable connective tissue'. It seems most likely that this effect of holothurin 1 on body wall dermis is mediated by constituent muscle cells, and the concept of 'mutable connective tissue' in echinoderms may therefore need to be re-evaluated to incorporate the involvement of muscle, as proposed recently for the spine ligament in sea urchins.
This article has been cited by other articles:
|
|
 |
|
  M. R. Elphick and M. C. Thorndyke Molecular characterisation of SALMFamide neuropeptides in sea urchins J. Exp. Biol., November 15, 2005; 208(22): 4273 - 4282. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Takemae and T. Motokawa Mechanical Properties of the Isolated Catch Apparatus of the Sea Urchin Spine Joint: Muscle Fibers Do Not Contribute to Passive Stiffness Changes Biol. Bull., February 1, 2005; 208(1): 29 - 35. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. F. Gainey Jr and M. J. Greenberg Nitric oxide mediates seasonal muscle potentiation in clam gills J. Exp. Biol., October 1, 2003; 206(19): 3507 - 3520. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Melarange and M. R. Elphick Comparative analysis of nitric oxide and SALMFamide neuropeptides as general muscle relaxants in starfish J. Exp. Biol., March 1, 2003; 206(5): 893 - 899. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. C. Wilkie Is muscle involved in the mechanical adaptability of echinoderm mutable collagenous tissue? J. Exp. Biol., January 15, 2002; 205(2): 159 - 165. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Hill Role of Ca(2+) in excitation-contraction coupling in echinoderm muscle: comparison with role in other tissues J. Exp. Biol., January 3, 2001; 204(5): 897 - 908. [Abstract] [PDF]
|
|
