Effects of anisosmotic stress on adult mammalian cardiac muscle
cell length, diameter, area and sarcomere length.
Tanaka, Ryuhei, Mary A. Barnes, George Cooper, Michael R. Zile.
Gazes Cardiac Research Institute, Cardiology Division of the
Department of Medicine, Medical University of South Carolina, and the
Ralph H. Johnson Department of Veterans Affairs Medical Center,
Charleston, South Carolina
APStracts 2:0457H, 1995.
The purpose of this study was to examine the effects of anisosmotic
stress on adult mammalian cardiac muscle cell (cardiocyte) size.
Anisosmotic stress was produced by altering superfusate osmolarity.
The resultant changes in cell size and sarcomere length (strain) were
measured. This method had not previously been examined in species
other than rodent and had not been examined when cardiocytes were
completely passive (i.e. when myofilament activation was limited).
One proposed determinant of the cellular response to anisosmotic
stress is a change in the relative passive stiffness. Accordingly,
cell size and sarcomere length were measured using a custom image
analysis system in enzymatically isolated cardiocytes from 10 normal
rats and 10 normal cats. Superfusate osmolarity measured by freezing
point depression was decreased from 300 +/- 6 to 130 +/- 5 mOsm by
adding distilled water and increased to 630 +/- 8 mOsm by adding
sucrose to Tyrodes solution. Cardiocyte size and sarcomere length
increased progressively when osmolarity was decreased from 630 +/- 8
to 300 +/- 6 to 130 +/- 5 mOsm. When osmolarity was decreased from
630_+/- 8 to 130 +/- 5 mOsm, there were no significant differences
between cat and rat cardiocytes with respect to percent change in
cardiocyte area (55 +/- 1% in cat vs 57 +/- 1% in rat) or diameter
(50 +/- 1% in cat vs 48 +/- 1 % in rat); however, there were
significant differences in cardiocyte length (2.8 +/- 0.3% in cat vs
6.1 +/- 0.3% in rat, p<0.05) and sarcomere length (3.3 +/- 0.3%
in cat vs 6.4 +/- 0.3 in rat, p<0.05). Thus, the osmolarity
gradient caused a significantly larger increase in length in rat
cells compared with cat cells suggesting a possible species dependent
difference in response to anisosmotic stress. To determine whether
these differences in length were related to diastolic interaction of
the contractile elements or differences in relative passive
stiffness, cardiocytes were subjected to the osmolarity gradient: 1)
during treatment with 7 mM 2,3-Butanedione Monoximine (BDM) which
inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM
ethylene glycol-tetraacetic acid (EGTA) a bivalent calcium chelator.
Treatment with EGTA or BDM abolished the differences between cat and
rat cardiocytes. Therefore, species dependent differences appeared to
be related to the degree of diastolic cross-bridge association and
not differences in relative passive stiffness. In conclusion, there
was a direct relation between superfusate osmolarity and the change
in each measurement of cell size and sarcomere length. The osmolarity
versus cell size relation appears to be useful in assessing the
cardiocyte response to anisosmotic stress and may in future studies
be useful in assessing changes in relative passive cardiocyte
stiffness produced by pathologic processes.
Received 4 January 1995; accepted in final form 21 September
1995.
APS Manuscript Number H3-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95