Spontaneously beating aggregates of 7-day embryonic chick myocytes were treated with two highly purified preparations of Clostridium perfringens neuraminidase. Both enzyme preparations were contaminated with variable amounts of a protein that electrophoretically co-migrated with a known standard of phospholipase C. Therefore, C. perfringens phospholipase C was used as a control in both beat rate and cell surface studies. The presence of sialic acid residues on the available myocardial cell surfaces present at the aggregate's periphery was confirmed by observing polycationic ferritin staining at pH 3.4, removal of stain by neuraminidase, and by acid methylation procedures. Neuraminidase treatment (1.2 U/ml for 2 h at 37°C) of either viable or fixed aggregates produced a reduction in stain at the cell surface. Although lower concentrations or shorter treatment times with neuraminidase resulted in little morphological change from controls, differences in aggregate beat rate could be detected with only 0.03 U/ml. The maximum response to the enzyme usually occurred within 10 to 30 min. Thereafter, contraction became arrhythmic. Phospholipase C was also effective in slowing beat rate and removing polycationic ferritin from the cell surface. This study demonstrates that sialic acid residues are present at the surface of embryonic chick myocardial cells as early as 7 days of development and that these monosaccharides, as well as phospholipids, may play a role in the maintenance of rhythmic beating.
ASJC Scopus subject areas
- Molecular Biology
- Cardiology and Cardiovascular Medicine