All of the following are involved in the transmission of regulatory signals through the ECF, except

When transmitted through gap junctions there is no involvement of ECF. Gap junctions are a specialized intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells. Hence there is a direct transpo without the involvement of ECF Ref guyton and hall textbook of medical physiology 12/e p45-46