Mapping action potentials and calcium transients simultaneously from the intact heart

Intracellular calcium handling plays an important role in cardiac electroph ysiology. Using two fluorescent indicators, we developed an optical mapping system that is capable of measuring calcium transients and action potentia ls at 256 recording sites simultaneously from the intact guinea pig heart. On the basis of in vitro measurements of dye excitation and emission spectr a, excitation and emission filters at 515 +/- 5 and >695 nm, respectively, were used to measure action potentials with di-4-ANEPPS, and excitation and emission filters at 365 +/- 25 and 485 +/- 5 nm, respectively, were used t o measure calcium transients with indo 1. The percent error due to spectral overlap was small when action potentials were measured (1.7 +/- 1.0%, n = 3) and negligible when calcium transients were measured (0%, n = 3). Record ings of calcium transients, action potentials, and isochrone maps of depola rization time and the time of calcium transient onset indicated negligible error due to fluorescence emission overlap. These data demonstrate that the error due to spectral overlap of indo 1 and di-4-ANEPPS is sufficiently sm all, such that optical mapping techniques can be used to measure calcium tr ansients and action potentials simultaneously in the intact heart.