Optical imaging analysis of the functional organization of the receptor-intracellular signal transduction system in the early embryonic heart.

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Voltage-sensitive dye-related absorption signals have provided a new method for monitoring spontaneous electrical activity in the early embryonic heart. We have introduced multiple-site optical recording of transmembrane voltage activity, using a fast merocyanine-rhodanine voltage-sensitive dye (NK2761) and a multi-element (16 X 16) photodiode array, to monitor action potentials in the early embryonic chick hearts at the stages when the first muscle contractions appear. By the application of adrenaline, the rhythm of the cardiac pacemaker became faster although the effect of this drug was very weak in comparison with that in adult hearts. On the other hand, the application of caffeine accelerated the rhythm of the pacemaker, suggesting that the intracellular signal transduction system was partially functioning. However, the application of adrenaline slowed the conduction velocity of the excitatory wave from the pacemaker. These results suggest that, in the early embryonic heart, the intracellular signal transduction system is somewhat different from that of adult hearts.