Hypothermic effects on action potential and force production of hedgehog and guinea pig papillary muscles

Action potentials and isometric force were recorded in papillary muscles from guinea pigs and summer hedgehogs at different temperatures between 37 and 0 degrees C. The action potential of the hedgehog was of a lower amplitude (mean 83 +/- 6 mV) than that of the guinea pig (mean 110 +/- 5 mV). The action potential duration at 50% repolarization was 22 +/- 2 msec in the hedgehog as compared to 105 +/- 11 msec in the guinea pig. Moreover, there was no distinct plateau phase of the hedgehog action potential. Lowering temperature prolonged the action potential duration in the two preparations by about the same percentage. However, the guinea pig preparation became progressively less excitable below 20 degrees C. Lowered temperature produced a positive inotropic effect in the guinea pig, whereas this effect was very slight in the hedgehog heart. Postextrasystolic potentiation was seen in the guinea pig but not in the hedgehog preparation. It is suggested that this difference between the preparations may be due to a greater relative amount of activator calcium in the hedgehog heart. The difference in cold tolerance between the preparations may reflect a difference in chemical composition of the sarcolemma.