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.
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Branton, D., Bullivant, S., Gilula, N.B., Karnovsky, M.J., Moor, H., Mühlethaler, K., Northcote, D.H., Packer, L., Satir, B., Satir, P., Speth, V., Staehelin, L.A., Steere, R.L., Weinstein, R.S.: Freeze-etching nomenclature. Science 190, 54–56 (1975)
Bullivant, S., Rayns, D.G., Bertaud, W.S., Chalcroft, J.P., Grayston, G.F.: Freeze-fractured myosin filaments. J. Cell Biol. 55, 520–524 (1972)
Clark, A.W., Branton, D.: Fracture faces in frozen outer segments from the guinea pig retina. Z. Zellforsch. 91, 586–603 (1968)
Da Silva, P.P.: Translational mobility of the membrane intercalated particles of human erythrocyte ghosts. J. Cell Biol. 53, 777–787 (1972)
Goodenough, D.A.: Bulk isolation of mouse hepatocyte gap junctions. J. Cell Biol. 61, 557–563 (1974)
Lorber, V., Rayns, D.G.: Cellular junctions in the tunicate heart. J. Cell Sci. 20, 211–227 (1972)
Markham, R., Frey, S., Hills, G.J.: Methods for the enhancement of image detail and accentuation of structure in electron microscopy. Virology 20, 88–102 (1963)
McNutt, N.S., Weinstein, R.S.: The ultrastructure of the nexus. J. Cell Biol. 47, 666–688 (1970)
McNutt, N.S., Weinstein, R.S.: Membrane ultrastructure at mammalian intercellular junctions. Progr. Biophys. molec. Biol. 26, 45–101 (1973)
Moor, H.: Die Gefrier-Fixation lebender Zellen und ihre Anwendung in der Elektronenmikroskopie. Z. Zellforsch. 62, 546–580 (1964)
Moor, H., Mühlethaler, K.: The fine structure of frozen etched yeast cells. J. Cell Biol. 17, 609–628 (1963)
Peracchia, C.: Low resistance junctions in crayfish. I. Two arrays of globulins in junctional membranes. J. Cell Biol. 57, 54–65 (1973a)
Peracchia, C.: Low resistance junctions in crayfish. II. Structural details and further evidence for intercellular channels by freeze-fracture and negative staining. J. Cell Biol. 57, 66–76 (1973b)
Pressman, B.C.: Ionophorous antibiotics as models for biological transport. Fed. Proc. 27, 1283–1288 (1968)
Singer, S.J., Nicolson, G.L.: The fluid mosaic model of the structure of cell membranes. Science 175, 720–731 (1972)
Staehelin, L.A.: Structure and function of intercellular junctions. Int. Rev. Cytol. 39, 191–283 (1974)
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Career Investigator of the American Heart Association
We 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
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Lorber, V., Rayns, D.G. Fine structure of the gap junction in the tunicate heart. Cell Tissue Res. 179, 169–175 (1977). https://doi.org/10.1007/BF00219794
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DOI: https://doi.org/10.1007/BF00219794