Action potential synchrony in embryonic precontractile chick heart: optical monitoring with potentiometric dyes.

1. Using an optical method for monitoring membrane potential, we recorded spontaneous action potentials simultaneously in several different areas of the 7-9 somite embryonic chick hearts. 2. Absorption signals resembling spontaneous action potentials were well synchronized among the different areas in the prebeating embryonic heart during the 7-9 somite stages of development, and the synchronization spread over the entire area of the heart. From these experimental results, it is evident that there is electrical coupling among embryonic chick heart cells even in the early stages of cardiogenesis. 3. When an embryonic heart was separated into right and left or anterior and posterior parts, the action potential synchrony between the two halves was completely blocked; however, the synchrony and the intrinsic rhythmicity in action potential recurrence remained in each part.