Davis PJ et al. - The nongenomic actions of thyroid hormone require a plasma membrane receptor or nuclear receptors located in cytoplasm. The plasma membrane receptor is located on integrin ?V?3 at the Arg-Gly-Asp recognition site important to the binding by the integrin of extracellular matrix proteins. l-Thyroxine (T4) is bound with greater affinity at this site than 3,5,3?-triiodo-l-thyronine (T3).