AJP - Cell Physiology, Vol 259, Issue 1 C144-C149, Copyright © 1990 by American Physiological Society
Morphological and functional characterization of the endosarcomeric elastic filament
G. Salviati, R. Betto, S. Ceoldo and S. Pierobon-Bormioli
Consiglio Nazionale delle Ricerche Centro di Studio per la Biologia e la Fisiopatologia Muscolare, Universita di Padova, Italy.
The elastic filament was studied in chemically skinned fibers from rabbit
psoas muscle by electron microscopy and resting tension measurements.
Extraction of skinned fibers with 40 mM sodium pyrophosphate caused a
selective removal of about two-thirds of the thick filaments and formed a
gap between the remaining portion of the A band and the I band. Very thin
filaments were seen in the gap and were decorated by anti-titin antibody.
The resting tension of these fibers was comparable to that of unextracted
control fibers. When the M band was completely extracted by a solution
containing 0.6 M NaCl, the resting tension completely disappeared at
sarcomere lengths from 2.8 to approximately 3.4 microns. These results
suggest that the elastic force of short sarcomeres is endowed in the titin
filaments and that these filaments are anchored to some structures of the Z
and M lines. Other filaments were found in the gap between the two I bands
of NaCl-extracted sarcomeres. These filaments differed from titin filaments
by a larger diameter and the anchoring points. They may represent the
sarcomeric structures responsible for the resting tension of extracted
fibers stretched at sarcomere lengths longer than 3.4 microns.
