Cyclic strain induces proliferation of cultured embryonic heart cells

Embryonic heart cells undergo cyclic strain as the developing heart circula tes blood to the embryo. Cyclic strain may have an important regulatory rol e in formation of the adult structure. This study examines the feasibility of a computerized cell-stretching device for applying strain to embryonic c ardiocytes to allow measurement of the cellular response. A primary cocultu re of myocytes and a secondary culture of nonmyocytes from stage-31 (7 d) e mbryonic chick hearts were grown on collagen-coated membranes that were sub sequently strained at 3 Hz to 20% maximal radial strain. After 24 h, total cell number increased by 37 +/- 6% in myocyte cocultures and by 26 +/- 6% i n nonmyocyte cultures over unstrained controls. Lactate dehydrogenase and a poptosis assays showed no significant differences in cell viabilities betwe en strained and unstrained cells. After 2 h strain, bromodeoxyuridine incor poration was 38 +/- 1.2% versus 19 +/- 0.2% (P < 0.01) in strained versus u nstrained myocyte cocultures, and 35 +/- 2.1% versus 16 +/- 0.2% (P = 0.01) in nonmyocyte cultures. MF20 antibody labeling and periodic acid-Schiff (P AS) staining estimated the number of myocytes in strained wells as 50-67% l arger than in control wells. Tyrosine phosphorylation may play a role in th e cellular response to strain, as Western blot analysis showed an increase in tyrosine phosphorylation of two proteins with approximate molecular weig hts of 63 and 150 kDa within 2 min of strain. The results of this study ind icate that embryonic chick cardiocytes can be cultured in an active mechani cal environment without significant detachment and damage and that increase d proliferation may be a primary response to strain.