Abstract: The present invention relates to a method for inducing myocardial cell proliferation. It is based, at least in part, on the discovery that adult human myocardial cells may be induced to proliferate in culture by exposure to a platelet freeze/thaw extract. The present invention provides for a method for inducing myocardial cell proliferation in vitro, as well as for myocardial cell cultures produced by this method. In a preferred embodiment, the invention provides for human myocardial cell cultures. The myocardial cell cultures of the invention may be used to study the physiology of cardiac muscle. In addition, they may be used to identify pharmaceutical agents that may be useful in the treatment of heart disease or, alternatively, agents that are cardiotoxic. Furthermore, the cultures of the invention may be used to provide myocardial cells that may be transplanted or implanted in a patient that suffers from a cardiac disorder.

Abstract: DNA cloning and expression vectors capable of replication in a microbial host comprising from upstream to downstream (a) at least one promoter; (b) a translation start codon; (c) a cloning segment which provides a means for inserting nucleic acid sequences and (d) a sequence coding for a detectable gene product, out of translational phase with the translation start codon but capable of being readjusted to the translational phase of said start codon by insertion into the cloning segment of nucleic acid sequences containing the proper number of nucleotides for readjustment, said gene product providing a means for detecting expression of inserted nucleic acid sequences.