Gap junctions is the right answer. The 2000 dalton molecule couldn't fit through them. The most well known function of the Gap junctions is in cardiac muscles where they promote transport of Ca2++ and contraction of the myocardium as one unit, otherwise contraction will be disorganized and ineffective. But gap junctions are present in most tissues of the body..
Tight junctions are the opposit, they prevent fluid and electrolytes to diffuse into tissues so that the only pathway for these substances to enter the tissue is through the cells, not inbetween them.