The overall focus of the work is the regulation of cardiac myocyte growth. The whole-organ correlate of this process, myocardial hypertrophy, is a significant problem in clinical cardiology. A cell culture model was developed, and has been used during past funding to explore basic mechanisms of myocyte growth stimulated by catecholamines through an alpha1-adrenergic receptor (AR). Whether the alpha1-AR-mediated growth observed in culture is actually relevant in vivo remains a very important question. Although work from this lab and others now indicates that cardiac myocytes can respond to multiple different growth factors, at least in culture models, considerable evidence has continued to accumulate that catecholamines, and an alpha1-AR in particular, might have an important regulatory role in vivo. This evidence provides a strong rationale for further study, but further study requires that the growth-related alpha1-AR be cloned. With a cDNA encoding the receptor, its presence in various forms of hypertrophy in different species and ages can be studied. Genetic experiments can be designed to test the cause-effect relationship of the receptor to hypertrophy in vivo. Novel and selective drugs can possibly be developed. Although several (three) alpha1-ARs have been cloned to date, the alpha1- AR related to growth in these cells has not been cloned. The alpha1-ARs are members of the superfamily of G protein-coupled receptors with 7 transmembrane domains. As with other receptors in this superfamily, dopamine and odorant, for example, there may be many alpha1-ARs, possibly with restricted tissue distribution and function. Therefore,the hypothesis of this work is that growth in neonatal rat cardiac myocytes is mediated by an alpha1-AR subtype, and the single aim is to obtain a cDNA encoding it. To obtain a cDNA, the polymerase chain reaction (PCR) will be used, with primer design based on homology among members of a gene family. The following criteria are proposed for concluding that a cDNA is that for the growth-related alpha1-AR. l) The corresponding mRNA is present in the cardiac myocytes. 2) The cDNA expressed in COS cells determines binding and CEC insensitivity consistent with that found for I-mediated myocyte growth. 3) The cDNA expressed in cardiac myocytes conveys enhanced sensitivity of growth and/or gene expression mediated by an alpha-1 agonist.
Showing the most recent 10 out of 60 publications
