Fig. 4. Cardiac sarcoplasmic reticulum vesicles from winter-hibernating ground squirrels exhibit faster Ca²⁺ uptake than those from autumn, non-hibernating individuals. The graph shows the normalized change in [Ca²⁺] in 1 ml of reaction medium after addition of 1 mg SR protein. The initial uptake rates for non-hibernating and hibernating groups were 137±13 and 235±17 nmol Ca²⁺min^-1mg^-1 SR protein, respectively (Tang et al., 1995).