Abstract
1. 1. The seasonal variations of force-frequency response of the atrium and papillary muscle were studied at 36, 25 13°C in hibernating and nonhibernating Richardson's group squirrel. 2. 2. At 36°C, a negative staircase (decreasing contraction force with increasing stimulation frequency) was obtained from nonhibernating ground squirrels sampled in December-February; however, a positive staircase was observed when the same preparations were tested at 25 and 13°C, suggesting differential temperature sensitivity in processes governing intracellular calcium regulation, i.e. sequestration, binding and uptake. 3. 3. Preparations sampled between February-April from both hibernating and nonhibernating squirrels and those from nonhibernating squirrels sampled in June, all showed positive staircase responses between 36 and 13°C. 4. 4. It is concluded that seasonal variations in force-frequency relation exist in the Richardson's ground squirrel but these variations are independent from the circannual changes in the state of hibernation.
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