Growth properties and biochemical characterization of collagens synthesized by adult rat heart fibroblasts in culture.

Collagen is the most important component of the extracellular matrix of the myocardium; it supports the myocytes and maintains the architecture of the heart. Collagen also participates in the myocardial response to various forms of pressure overload. Increased tissue collagen content occurs as a result of spontaneous or experimental overload-induced myocardial hypertrophy. In order to determine the mechanisms responsible for the increased collagen deposition in experimental cardiac hypertrophy, we established monolayer cultures of fibroblasts isolated from normal adult rat myocardium and studied their growth and biosynthetic characteristics. These cells have a doubling time of about 20h and synthesize and secrete several collagenous and non-collagenous proteins. We found that type I collagen was the major collagenous product of these cells representing 80% of total newly synthesized collagen. Most of the newly synthesized collagen was secreted into the culture medium as intact and partially cleaved procollagens. About 20% of the total collagen synthesized was type III collagen which was also secreted into the medium as a procollagen. A small proportion of type V collagen (less than 5%) was also synthesized by these cultures. Fibronectin which was identified by its mobility in SDS gel electrophoresis was quantified by immunoprecipitation with specific antisera and was the most abundant non-collagenous protein synthesized by these cells. Northern blot hybridization analysis demonstrated that these cells expressed transcripts for alpha 1 chains of types I and III collagen and for fibronectin.