Synchronization of pulsation rates in isolated cardiac myocytes

Abstract

Cells dissociated from seven-day embryonic chick hearts were cultured at low density in low-potassium medium for 4–24 h. Pairs of spontaneously beating myocytes, attached 2–5 μm apart to the bottom of the culture dish were observed until they first established physical contact with each other, and then until they synchronized their separate beats to a common rhythm. The cells were immediately fixed, stained and embedded on the plate, and prepared for electron microscopy. The interval between initial contact and synchrony was determined in 15 cell pairs to range from 4–38 min (mean = 16.5 min). Of 25 cell pairs that attained synchronous rhythms, only eight entrained at a rate equal to the faster member of the pair. Eleven pairs synchronized at a rhythm equal to or slower than that of the slower member; six had intermediate rates. Electron micrographs of the region of contact revealed small sites of close membrane apposition.