Match the descriptions to the correct type of signaling. Nitric oxide will diffuse from endothelial cells to neighboring smooth muscle cells, signaling muscle cell relaxation. Some cancer cells will produce a growth factor to which they respond, driving unregulated proliferation. Substance X synthesized in neurons travels through gap junctions, and triggers the transduction of an electrochemical signal. The growth hormone released from the pituitary affects many different types of cells throughout the body. .