In vitro differentiation of rabbit blastocyst cells

Six- and seven-day post-coitus (p.c.) rabbit embryos have been cultured in an attempt to establish a trophectodermal cell line. Results indicate that cells with epithelial characteristics (i.e. positive staining for cytokeratin) will survive in culture until Passage 3. At that time a fibroblastlike cell becomes predominant. In addition, we have found that the presence of the inner cell mass is required for trophectodermal cells from 6-d p.c. embryos to attach to the collagen substrate. Culture of 7-d p.c. embryo explants often results in the development of cells that spontaneously contract. These cells stain positively for myosin, which indicates that they may be precardiac cells. Maximum diastolic potential was -59 +/- 1.2 mV and the threshold potential was -53 +/- 2.3 mV. Spontaneously contracting cells did not respond to atropine, acetylcholine, epinephrine, isoproterenol, or propranolol. Action potential seems to be a result of an inward calcium current, because the beating rate is decreased in a dose-related manner with the calcium channel blocker verapamil, whereas the voltage-sensitive sodium channel blocker tetrodotoxin was without effect.