Use of 5-Bromodeoxyuridine and irradiation for the estimation of the myoblast and myocyte content of primary rat heart cell cultures

A method for killing dividing cells was adapted for the elimination of dividing heart muscle cells (myoblasts) in cultures. We have used this method to demonstrate their presence and to estimate their number as well as the number of nondividing heart muscle cells (myocytes) in the neo-natal rat heart. Cells were cultivated in BUdR (5-bromodeoxyuridine) 10-4 M for 3 days and then irradiated with long uv light. The selective elimination of dividing cells led to a loss of myosin Ca2+-activated ATPase in the cultures. The percent of ATPase left after irradiation was 32% of the control in cultures derived from 1-day postnatal rats and 48% in cultures from 4-day postnatal rats. This reflects an in vivo shift of myoblasts to myocytes in the muscle cell population as the rat ages