Russell Ross's study investigates the growth and differentiation of smooth muscle cells derived from the inner media and intima of immature guinea pig aortas in culture. The cells maintained their smooth muscle morphology throughout the 8-week culture period, growing in multiple overlapping layers. By 4 weeks, microfibrils (110 Å) and basement membrane-like material appeared between the cell layers. Amino acid analysis of the microfibrils showed a composition similar to that of elastic fiber microfibrils. These findings, combined with radioautographic evidence of extracellular protein synthesis, confirm that these cells are connective tissue synthetic cells. The study also highlights the formation of elastic fibers and basement membrane-like structures, which are crucial for connective tissue formation. The smooth muscle cells' ability to synthesize and secrete extracellular proteins suggests their role in connective tissue development, potentially linking them to fibroblasts, osteoblasts, and chondroblasts. The research provides insights into the mechanisms of atherogenesis and the synthesis of elastic fiber proteins in vitro.Russell Ross's study investigates the growth and differentiation of smooth muscle cells derived from the inner media and intima of immature guinea pig aortas in culture. The cells maintained their smooth muscle morphology throughout the 8-week culture period, growing in multiple overlapping layers. By 4 weeks, microfibrils (110 Å) and basement membrane-like material appeared between the cell layers. Amino acid analysis of the microfibrils showed a composition similar to that of elastic fiber microfibrils. These findings, combined with radioautographic evidence of extracellular protein synthesis, confirm that these cells are connective tissue synthetic cells. The study also highlights the formation of elastic fibers and basement membrane-like structures, which are crucial for connective tissue formation. The smooth muscle cells' ability to synthesize and secrete extracellular proteins suggests their role in connective tissue development, potentially linking them to fibroblasts, osteoblasts, and chondroblasts. The research provides insights into the mechanisms of atherogenesis and the synthesis of elastic fiber proteins in vitro.