Functional pacemaking area in the early embryonic chick heart assessed by simultaneous multiple-site optical recording of spontaneous action potentials.
Pacemaking areas in the early embryonic chick hearts were quantitatively assessed using simultaneous multiple-site optical recordings of spontaneous action potentials. The measuring system with a 10- X 10- or a 12 X 12-element photodiode array had a spatial resolution of 15-30 microns. Spontaneous action potential-related optical signals were recorded simultaneously from multiple contiguous regions in the area in which the pacemaker site was located in seven- to nine-somite embryonic hearts stained with a voltage-sensitive merocyanine-rhodanine dye (NK 2761). In the seven- to early eight-somite embryonic hearts, the location of the pacemaking area is not uniquely determined, and as development proceeds to the nine-somite stage, the pacemaking area becomes confined to the left pre-atrial tissue. Analysis of the simultaneous multiple-site optical recordings showed that the pacemaking area was basically circular in shape in the later eight- to nine-somite embryonic hearts. An elliptical shape also was observed at the seven- to early eight-somite stages of development. The size of the pacemaking area was estimated to be approximately 1,200-3,000 micron2. We suggest that the pacemaking area is composed of approximately 60-150 cells, and that the pacemaking area remains at a relatively constant size throughout the seven- to nine-somite stages. It is thus proposed that a population of pacemaking cells, rather than a single cell, serves as a rhythm generator in the embryonic chick heart.
Kamino
K
K
Department of Physiology, Tokyo Medical and Dental University School of Medicine, Japan.
Komuro
H
H
Sakai
T
T
Hirota
A
A
D000200:Action Potentials; D000818:Animals; D002642:Chick Embryo; D006329:Heart Conduction System / Q000196:embryology* / Q000502:physiology