Ultrastructural evidence for sinusoid spaces and coupling between pituicytes in the rat

Summary The pericapillary palisade of the rat neurohypophysis was examined by means of thin-section and freeze-etch electron-microscopy. Special attention was given to pituicyte processes intermingled with neurosecretory terminals. These processes are identified by the presence of lipid droplets and ribosomes.Extracellular spaces are conspicuously enlarged in circumscribed regions between fingerlike protrusions of pituicyte processes. Neurosecretory axons seem to have free access to these enlarged spaces. Zonulae occludentes often combined with small gap junctions are found at the border of these sinusoid spaces. Gap junctions and occasionally intermediate junctions are seen between pituicyte processes. The topographic relationship and the functional significance of these structural features remain to be further elucidated.Supported by Grants of the Dr. Eric Slack-Gyr Foundation, Zürich, the Swiss National Foundation for Scientific Research Nrs. 3.823.72, 3.774.72, 3.712.72 and 3.045.73, the EMDO-Foundation and the Hartmann-Müller-Foundation for Medical Research at the University of Zürich. A short account has been presented at the meeting of the Union of Swiss Societies for Experimental Biology, April 1975 (Experientia 1975, in press).     

Fine structure of the gap junction in the tunicate heart

Summary The plasma membranes of the tunicate heart exhibit an abundance of macular gap junctions distributed widely over the membrane surface. A study of these junctions by the freeze-etch technique was undertaken in an effort to elucidate the fine structure of this important membrane modification in a primitive heart. In cross or near-cross fractured junctions the junctional particles in contiguous membranes appear to be paired in register and to meet in the midline. In favorable face views, the junctional particles are seen to be disposed in hexagonal array. The individual particles display a distinct rosette-like substructure consistent with a six-membered ring of globular protein molecules clustered around a central channel. Similar junctional-type particles can be found in nonjunctional areas of membrane suggesting that the transport mechanism which they may represent is not restricted to the gap junction.Career Investigator of the American Heart AssociationWe wish to thank Dr. J.B. Jillett for use of the facilities of the Portobello Marine Biological Station; Mr. W.S. Bertaud, Physics and Engineering Laboratory, D.S.I.R., Lower Hutt, who kindly supervised the preparation of some of the freeze-etch replicas; Dr. R.H. Millar of the Dunstaffnage Marine Research Laboratory, Oban, Argyll, Scotland, who identified the tunicate used in the present (and previous) study; Prof. W.D. Trotter who made facilities in the Department of Anatomy, University of Otago Medical School, Dunedin, available to one of us (V.L.); and Mrs. S.M. O'Kane for excellent technical assistance. Generous support from the American Heart Association (to V.L.) and from the Medical Research Council of New Zealand (to D.G.R.) is gratefully acknowledged     

Gap junctions of the muscles of the small and large intestine

Summary The distribution of gap junctions (nexuses) in various parts of the small and large intestines of the guinea-pig was studied using the freeze-fracture technique and in thin sections. The percentage area of smooth muscle cell surface occupied by gap junctions varies from 0.50% in the circular muscle of the duodenum to zero in the longitudinal muscle of the ileum. In the circular muscle of the jejunum and ileum the area occupied by nexuses is 0.22% (or about 11 m² per cell). The sizes of junctions range from less than 0.01 m² to 0.20 m², with two-thirds of them being smaller than 0.05 m². In the colon, gap junctions are rare, very small and confined to the circular muscle layer. Even the smallest aggregates of intramembrane particles correspond to areas of close apposition between the membranes of adjacent cells; it is therefore justified to interpret them as being gap junctions. Some gap junctions are formed between a smooth muscle cell and an interstitial cell. Gap junctions are not found in the longitudinal muscle of the small intestine; this is in sharp contrast to the abundance of gap junctions in the adjacent circular layer.In the small intestine of cats and rabbits, gap junctions are abundant in the circular muscle layer, whereas they are very small in size and very few in number in the longitudinal muscle layer.The authors wish to thank Mr Peter Trigg and Miss Eva Franke for help and support. This work was supported by grants from the Medical Research Council and the Central Research Fund of the University of London     

Ian Humphery-Smith on current challenges in proteomics

Ian Humphery-Smith is Professor of Pharmaceutical Proteomics at Utrecht University, The Netherlands, and until recently was a Managing Director and Chief Scientific Officer of Glaucus Proteomics. After a PhD in Parasitology at the University of Queensland, he studied virology and bacteriology in France as a post-doc, before returning to Australia as Course-Coordinator in Medical Microbiology and Immunology at the University of Sydney. During this time, Humphery-Smith took up the posts of Executive Director of Australia's second largest DNA sequencing facility and Director of the Center for Proteomic Research and Gene-Product Mapping, which later became the world's first center to focus on studying the proteome. Humphery-Smith has devoted ten years of research to analyzing proteins in health and disease, and it was his work that originally coined the term ‘proteomics’. He was the first to publish the most complete analysis of an entire proteome in 2000, that of the bacterium Mycoplasma genitalium. He currently serves as a council member of the Human Proteome Organization (HUPO) and has been a prime mover in efforts to have the Human Proteome Project become a formally-ratified international initiative to follow-on from the Human Genome Project.