Evidence points towards the requirement for 'gap junctions' in the mediation of EDHF responses. Gap junctions are specialised pores which allow small molecules and charge to pass between cells. They are found between endothelial cells and the underlying muscle of the blood vessel. A drug called Rotigaptide has been developed to cause gap junctions to open. It has been safely administered in healthy volunteers and is now in a Phase II drug trial. By opening gap junctions the investigators hypothesise that it could increase EDHF mediated activity and vasodilatation. It represents a useful tool with which to examine the role of gap junctions in EDHF activity in vivo.