Optical signals from early embryonic chick heart stained with potential sensitive dyes: evidence for electrical activity.

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Abstract
Using an optical method for monitoring membrane potential, spontaneous electrical activity in the very early embryonic chick heart at the 7-9 somite stages was measured. Spontaneous absorption signals from the 7-8 somite embryonic chick hearts stained with a potential sensitive merocyanine-oxazolone dye were demonstrated. The signals were observed also when a merocyanine-rhodanine dye was used. These signals were identified as spontaneous electical activity in the embryonic heart cells. The action spectrum in absorption of the merocyanine-oxazolone dye was triphasic in early embryonic chick heart with an increase in transmittance from 750 to 700, a decrease from 700 to 600 and an increase from 600 to 525 nm. The magnitude of the signal was about 10-3 of the resting intensity at 675 nm, with the merocyanine-oxazolone dye. The spontaneous absorption signals had a signal-to-noise ratio of about 10, respectively. The absorption signals were markedly depressed by a higher external K+ concentration; they were not affected by tetrodotoxin (TTX). Apparently spontaneous electrical activity is generated at the 7-9 somite developmental stages, i.e., before the initiation of the heartbeat.