Journal of Muscle Research & Cell Motility

, Volume 7, Issue 6, pp 568–578

An unusual Z-system in the obliquely striated muscles of crinoids: three-dimensional structure and computer simulations

  • M. Daniela Candia Carnevali
  • Abele Saita
  • Alessandra Fedrigo
Article

DOI: 10.1007/BF01753572

Cite this article as:
Candia Carnevali, M.D., Saita, A. & Fedrigo, A. J Muscle Res Cell Motil (1986) 7: 568. doi:10.1007/BF01753572

Summary

The peculiar functional structure of the Z-line in the obliquely striated muscles of some feather stars is described. It is known that cross-striated muscles are characterized by linear and continuous Z-bands, and obliquely striated muscles by disconnected, obliquely aligned Z-elements. Owing to this discontinuous organization, the sarcomere can perform wide active lengthenings, shortenings, and even ‘super-elongations’ in the helical fibres. In contrast, the obliquely striated fibres of crinoids show markedly continuous and homogeneous oblique Z-lines; such a structure is not compatible with ‘super-performances’ like sliding and shearing of the sarcomere elements, but instead could allow functions comparable to those characteristic of a cross-striated muscle (quick, short movements, mechanically amplifiable by bone levers). This odd situation, only interpretable in terms of evolutionary constraint, could be considered opposite and symmetrical to that of cross-striated ‘super-contracting’ muscles, where the Z-line is exceptionally fragmented to allow the sarcomere to super-contract.

The possible architecture of a significant parameter such as the Z-line, which determines muscle fibre potential capacities, is analysed in detail: (1) through qualitative-quantitative evaluation of electron micrographs, supported by statistical analysis of the data; and (2) bycomputer simulations. The data obtained suggest that the most realistic conformation of the whole Z-complex in these muscles consists of a multiple system of continuous, ribbon-like helical planes running in parallel along the fibre from end to end and regularly cutting it with a constant thickness. The proposed model seems morphologically compatible with the experimentally verified situations and functionally compatible with the mechanical requirements for a normal contraction and for a balanced distribution of the involved strengths.

Copyright information

© Chapman and Hall Ltd 1986

Authors and Affiliations

  • M. Daniela Candia Carnevali
    • 1
  • Abele Saita
    • 2
  • Alessandra Fedrigo
    • 1
  1. 1.Dipartimento di BiologiaUniversità di MilanoMilanoItaly
  2. 2.Dipartimento di Fisiologia e Biochimica generaliUniversità di MilanoMilanoItaly