Irradiance dependence of the conduction block of an in vitro cardiomyocyte wire.

BACKGROUND: To obtain therapeutic condition precisely by in vitro experiment, we studied the irradiance dependence of the electrical conduction blockage caused by a photodynamic reaction using a high extracellular concentration of talaporfin sodium on a novel in vitro cardiomyocyte electrical conduction wire.

METHODS: The cardiomyocyte wires were constructed on patterned cultivation cover glass, which had cultivation areas 60μm in width, and a maximum length of 10mm. The talaporfin sodium concentration was set to 20μg/mL. The photodynamic reaction with a high extracellular photosensitizer concentration was performed with a short time interval (approximately 15min) between photosensitizer exposure and irradiation. A 663-nm laser was applied to the cardiomyocyte wire, and the irradiance was varied between 3 and 120mW/cm2 . The cardiomyocyte electrical conduction was evaluated using the cross-correlation function of intracellular Ca2+ probe fluorescence brightness from an upper and lower section outside the laser irradiation area of a wire every 10s, which lasted up to 600s.

RESULTS: The onset of electrical conduction blockage was defined by an 85% decrease in the cross-correlation function, compared with its initial value. The time for the electrical conduction blockage decreased from 600 to 300s as the irradiance was increased. Also, the probability of electrical conduction blockage was found to increase with increasing irradiance.

CONCLUSIONS: We found a strong dependence on the irradiance for the time and probability of electrical conduction blockage.