Figure 4. Correlation analysis of calcium parameters among cells isolated from CR_3–5 and CR₄ .

The first quartile (fast‐relaxing delineation) and third quartile (slow‐relaxing delineation) of RT₅₀ values are indicated by the vertical dashed lines. Neither Ca‐DT₅₀ (A), nor the peak fluorescence ratio (B) of the Fura‐2 Ca²⁺ indicator was correlated with RT₅₀. C, representative records showing independence of RT₅₀ from the shape of the intracellular calcium transient. These records were obtained in fast‐relaxing and slow‐relaxing cells within CR₄ of the same rat. The normalized Ca²⁺ transients of these two cells were almost identical, yet their relaxation behaviours were strikingly different. The inset shows bright‐field images of the cells from which these records were taken.