The A7r5 fibroblast cell line was initiated from smooth muscle tissue excised from the thoracic aorta of a rat embryo (DB1X strain). Similar to other smooth muscle cells, A7r5 cells produce muscle-type isoenzymes, including myokinase and creatine phosphokinase. Activity of the isoenzymes increases when cultures of A7r5 cells reach a stationary phase. The fibroblasts also produce myosin, the protein that provides muscle with its characteristic elastic and contractile properties. Typical applications of the A7r5 line include biophysical and biochemical studies.

Vascular smooth muscle, such as the tissue from which the A7r5 cell line was developed, is a type of non-striated muscle specifically found in the walls of blood vessels. The aorta and other arteries contain significantly more smooth muscle tissue than do veins and have correspondingly thicker walls. Nerve stimulation is not required to stimulate smooth muscle cells, which usually contract involuntarily. In the body, the contraction of vascular smooth muscle facilitates the movement of blood through the circulatory system.

The cytoskeletal filamentous actin network was targeted in a culture of A7r5 rat thoracic aorta cells with phalloidin conjugated to Alexa Fluor 350. Phalloidin is a member of the phallotoxin group of bicyclic peptides isolated from the deadly Amanita phalloides mushroom. The cell culture was also labeled for mitochondria with MitoTracker Red CMXRos and counterstained for the nucleus with SYTOX Green. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.