Abstract
1. The effect of temperature on the mechanical properties and the action potential of isolated frog ventricle were studied.
2. On cooling to between 25°C and 8°C, the maximal tension and the contraction time increased while the maximal rate of rise of tension decreased, and the values of Q10 were 1/1.82, 1/2.32 and 1.26 respectively. The maximal rate of proportional rise of tension, i. e. the ratio of the maximal rate of rise of tension devided by the maximal tension, decreased on cooling, and Q10 of it was equal to the reciprocal Q10 of the contraction time.
3. The force-velocity curve was hyperbolic at 8°C, but rather linear at 23°C.
4. Not only the duration but also the intensity of the active state increased on cooling, and Q10 of them were about 1/2.6 and 1/1.5 respectively.
5. The work performed depended on the initial length of the muscle, the load and the temperature. Under the condition that the muscle was encounted by inertia force, however, more work than expected from above three factors was performed, accompanying the slowing of contraction.
6. Q10 of the duration of action potential was 1/1.52, this is quite different from Q10 of the contraction time or the duration of the active state.
7. The relation between the active state and calcium movement, and the energy mobilizing mechanism in cardiac muscle were discussed.
