The staircase phenomenon and the strength-interval relationship of contractions in cultured cells of chicken embryonic ventricles.
The staircase phenomenon and the relationship between contraction strength and stimulation interval were investigated in single or aggregated cells cultured from 5-, 12-, and 19-d-old chicken embryonic ventricles. Within 24 h after start of cultivation was begun, the cells were separated and spontaneously inactive. However, they contracted when electrical stimulation was applied. The modes of a staircase phenomenon and a strength-interval relationship varied, depending on a few conditions such as the ages of the embryos, the presence of spontaneous activities and the composition of the bathing solution. The 19-d-old cells, which formed an aggregate and exhibited spontaneous activities, showed a negative staircase phenomenon and the negative strength-interval relationship when they were bathed in a culture medium containing bovine serum. The 12-d-old cells demonstrated a less distinct staircase and a flat strength-interval relationship. Both 19- and 12-d-old cells showed a positive relationship, if they were cultured for less than 48 h and were spontaneously inactive, or if they were bathed in Tyrode solution during the experiments. The 5-d-old cells showed the positive staircase whether they were spontaneously active or not. The developmental change in the interval-dependency of contraction can be explained by the functions of the sarcoplasmic reticulum (SR), although Ca2+ current and the Na(+)-Ca2+ exchange mechanism should be involved. The function of the SR develops progressively during the embryonic stage and plays an important role in regulation of the contraction-relaxation cycle at the late stage before hatching.
Toyota
H
H
Department of Physiology, Kawasaki Medical School, Kurashiki, Japan.
Matsumura
M
M
D000818:Animals; D002455:Cell Division; D002642:Chick Embryo; D006321:Heart / Q000196:embryology*; D006352:Heart Ventricles; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology