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Effect of temperature and calcium on the diastolic length-tension relationship of rat heart muscle.

Experiments were performed on strips from the right ventricle of the rat in order to investigate the influence of temperature and Ca++-removal on the length-tension relationship. Temperature change (22-38 degrees) had no effect on the resting, non-stimulated muscle. The isometric minima curves of the electrically stimulated preparations at 18 degrees and 38 degrees (diastolic length-tension relationship), however, were shifted to the right compared to those at 28 degrees. When temperature decreased (at fixed muscle length), the diastolic tension surmounted a maximum at the optimal temperature (28 degrees) and declined with further cooling. Moreover the electrolyte exchange characteristics (Ca, K, Na), which follow upon a variation in temperature, were studied. The calcium content of the stimulated preparations showed a similar dependence on temperature as the diastolic tension, indicating that calcium might play a role with respect to the influence of temperature on the diastolic length-tension relationship. Indeed an addition of EDTA to the bath solution caused a parallel shift of the isometric minima curve to the right. These results show that an active mechanism might contribute to the increase of diastolic tension in response to stretch.