Cold acclimation of guinea pig depressed contraction of cardiac papillary muscle.
Guinea pigs were exposed to 5 degrees C for 3 wk, and the contractions of myocardial papillary muscle were compared with preparations dissected from control animals kept at approximately 25 degrees 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.
Takagi
S
S
Departments of Physiology and Cardiovascular Medicine, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Kihara
Y
Y
Toyoda
F
F
Morita
T
T
Sasayama
S
S
Mitsuiye
T
T
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D003080:Cold Temperature; D004594:Electrophysiology; D006168:Guinea Pigs; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D013997:Time Factors
D012433:Ryanodine; D011188:Potassium