Vol. 276, Issue 4, R923-R928, April 1999
Cold acclimation of guinea pig depressed contraction of
cardiac papillary muscle
Shuichi
Takagi1,
Yasuki
Kihara1,
Futoshi
Toyoda2,
Tetsuo
Morita3,
Shigetake
Sasayama1, and
Tamotsu
Mitsuiye1
1 Departments of Physiology and
Cardiovascular Medicine, Faculty of Medicine, and
2 Department of Animal Husbandry
Resources, Faculty of Agriculture, Kyoto University, Sakyo-ku,
Kyoto 606-8501; and 3 Department
of Animal Science, Faculty of Agriculture, Miyazaki University,
Miyazaki 899-2192, Japan
Guinea pigs were exposed to 5°C for 3 wk, and the contractions of myocardial papillary muscle were compared
with preparations dissected from control animals kept at ~25°C.
Developed tension of the papillary muscle per cross-sectional area was
significantly (t-test,
P < 0.05) decreased after cold
exposure (19,200 ± 8,160 vs. 3,020 ± 2,890 dyne/cm2; 1 Hz). Time to peak
tension was significantly faster in cold-exposed guinea pigs (126.4 ± 11.1 ms; 1 Hz) than in controls (162.7 ± 8.7 ms). The
magnitude of the developed tension after application of ryanodine (2 mM) to muscles from cold-exposed animals was decreased to 37.5 ± 8.3% of control at 1 Hz, whereas in muscles from control animals,
tension was decreased to 82.4 ± 7.7%. The ryanodine-sensitive component of contraction was not significantly changed in control guinea pigs at frequencies >0.5 Hz, whereas in muscles from
cold-acclimated guinea pigs, there was a "positive staircase."
These results suggested that reversal of the
Na+/Ca2+
exchanger is predominantly involved in the positive staircase in
control guinea pigs, whereas rate-dependent increases in the Ca2+ store in the sarcoplasmic
reticulum may be involved in the staircase after cold acclimation.
ryanodine; sarcoplasmic reticulum; sodium/calcium ion exchange
