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Fig. 7. ß-adrenergic stimulation induces positive inotropy by recruitment of central RyRs. (A) A cell image showing the locations of the subsarcolemmal site (red circle) and the central non-regenerative region (green circle) that were analysed. (B,C) The response of the cell before and following a 3-minute incubation with isoproterenol (0.1 µM). The red and green traces depict the change in Ca²⁺ concentration at the subsarcolemmal and central region, respectively. The blue traces depict the ratio of the Ca²⁺ response at the subsarcolemmal site relative to that inside the cell. The upward deflection represents a subsarcolemmal response with a lesser central Ca²⁺ signal. Note that in the isoproterenol stimulated cell (C), the ratio of subsarcolemmal/central Ca²⁺ response increases quickly, as in the control situation. However, the ratio more rapidly declines and undershoots, owing to the development of the central Ca²⁺ response. The contraction of the cell is shown by the black traces. The spatial properties of the Ca²⁺ signal are illustrated by the pseudo-linescan images in Bb and Cb. The dashed yellow lines and arrowheads indicate the points at which the cell was depolarised. The dashed black line on the cell image in A shows the portion of the cell that was sampled in generating the pseudo-linescan plots. The data shown are from a representative cell typical of eight other cells analysed (from three hearts).

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