associated with gap junctions and proposing the vesicle contents may move across the junction plaques between two cells were rare, as most studies focused on the connexons rather than vesicles. A later study using a combination of microscopy techniques confirmed the early evidence of a probable function for gap junctions in intercellular vesicle transfer. Areas of vesicle transfer were associated with connexin free islands within gap junction plaques. Connexin 43 has been shown to be necessary for the transfer of whole mitochondria to neighboring cells though whether the mitochondria is transferred directly through the membrane or within a vesicle is not determined Electrical and chemical nerve synapses Because of the widespread occurrence of gap junctions in cell types other than nerve cells the term gap junction became more generally used than terms such as electrical synapse or nexus. Another dimension in the relationship between nerve cells and gap junctions was revealed by studying chemical synapse formation and gap junction presence. By tracing nerve development in leeches with gap junction expression suppressed it was shown that the bidirectional gap junction (electrical nerve synapse) needs to form between two cells before they can grow to form a unidirectional "chemical nerve synapse". The chemical nerve synapse is the synapse most often truncated to the more ambiguous term "nerve synapse". Composition Connexins The purification of the intercellular gap junction plaques enriched in the channel forming protein (connexin) showed a protein forming hexagonal arrays in x-ray diffraction. Now the systematic study and identification of the predominant gap junction protein became possible. Refined ultrastructural studies by TEM showed protein occurred in a complementary fashion in both cells participating in a gap junction plaque. The gap junction plaque is a relatively large area of membrane observed in TEM thin section and freeze fracture (FF) seen filled with trans-membrane proteins in both tissues and more gently treated gap junction preparations. With the apparent ability for one protein alone to enable intercellular communication seen in gap junctions the term gap junction tended to become synonymous with a group of assembled connexins though this was not shown in vivo. Biochemical analysis of gap junction rich isolates from various tissues demonstrated a family of connexins. Ultrastructure and biochemistry of isolated gap junctions already referenced had indicated the connexins preferentially group in gap junction plaques or domains and connexins were the best characterized constituent. It has been noted that the organisation of