Cold adaptation suppresses the contractility of both atrial and ventricular muscle of the crucian carp heart

Abstract

Adaptation to low temperature in crucian carp Carasius carassius increases twitch duration both in atrial and ventricular muscle and the response is largely explained by a temperatureinduced reduction in myofibrillar ATPase activity. The prolonged twitch increases the refractoriness of both atrial and ventricular muscle, i.e. the optimal force development is achieved at longer diastolic intervals after acclimation to cold. The contractions of atrial and ventricular muscle are insensitive to 10 μ ryanodine, an inhibitor of SR release Ca2+ channel but sensitive to 20 μ verapamil, a blocker of L‐type Ca2+ channels. This suggests that E‐C‐coupling in the crucian carp heart is exclusively based on extracellular Ca2+ sources. The present findings indicate that cold‐acclimation slows the contraction kinetics of the crucian carp heart and thereby preconditions the cardiac muscle for a low energy supply during winter anoxic conditions.