Da. Lowe et al., ECCENTRIC CONTRACTION-INDUCED INJURY OF MOUSE SOLEUS MUSCLE - EFFECT OF VARYING [CA2+](O), Journal of applied physiology, 76(4), 1994, pp. 1445-1453
The objective of this study was to determine the effect of varying ext
racellular Ca2+ concentration (Ca2+(o)) on eccentric contraction-ind
uced muscle injury. Isolated mouse soleus muscles (n = 64) performed e
ither 20 eccentric or 20 isometric contractions over a 40-min period i
n a Krebs buffer containing 0.5, 1.25, or 5.0 mM Ca2+. Measurements of
contractile function and lactate dehydrogenase accumulation in the bu
ffer were then made every 15 min for 2 h. Prostaglandin E(2), leukotri
ene B-4, and tyrosine accumulation in the incubation medium and total
muscle Ca2+ were measured at the end of the experiment. Reductions i
n maximal isometric tetanic force for muscles immediately after perfor
mance of 20 eccentric and 20 isometric contractions were 21.1 +/- 1.4
and 1.2 +/- 0.7%, respectively. Total muscle Ca2+ was 28-37% higher
in muscles that performed eccentric contractions than in those that pe
rformed isometric contractions. However, estimates made with a confoca
l laser scanning microscope and fluo 3 do not indicate that there was
a difference in free cytosolic Ca2+ between fibers from injured and
control muscles. Also, leukotriene B-4, prostaglandin E(2), and tyrosi
ne accumulation in the buffer from muscles that performed eccentric co
ntractions was not elevated over that from muscles that performed isom
etric contractions. Furthermore, lactate dehydrogenase accumulation an
d reductions of contractile function over the 2-h incubation period we
re not enhanced by higher Ca2+(o) or influenced by the type of contr
action. These findings suggest that muscles that were injured by eccen
tric contractions were able to buffer the increased influx of extracel
lular Ca2+, maintain a normal free cytosolic Ca2+, and avoid activat
ion of Ca2+-sensitive degradative pathways.