Figure 7. Simultaneous recordings of APs and intracellular Ca²⁺ transients.

APs and Ca_i transients were mapped simultaneously from Langendorff perfused hearts that were stained with both PGH I and Rhod-2 by focusing images of the heart on 2 16×16 elements photodiode arrays (Choi et al., 2002; Choi & Salama, 2000).

A: Simultaneous AP and Ca_i recordings from a guinea pig heart. The superposition of APs and Ca_i transients recorded from 2 diodes, one on the ‘voltage’ array the other diode from the ‘calcium’ array where both diodes are aligned to view the same 0.9 × 0.9 mm² region of epicardium.

B: Simultaneous AP and Ca_i recordings from a rabbit heart

APs and Ca_i transients as in (A), except that the recordings were made from a pre-pubertal female rabbit heart at slow (a) and fast (b) sweep speed. The addition of E4031 (0.5 μM), a known blocker of I_Kr (the fast component of the delayed rectifying K⁺ current) caused a marked prolongation of the AP duration which was readily measured with PGH I (traces c). Longer excitation wavelength (690 instead of 540 nm) caused the inversion of ΔF and an inverted AP (c).

C. Simultaneous AP and Ca_i recordings for an FVB mouse heart

Langendorff perfused mouse hearts were stained with a PGH I stock solution (2 mM in Tyrode’s solution at pH 6.0) and Rhod-2/AM. The superposition of AP and Ca_i traces from 2 diodes viewing the same region of myocardium (250 × 250 μm²) show that for mouse ventricular muscle the Ca_i transients are considerably longer than the AP.