Submicroscopic Organization of the Postsynaptic Membrane in the Myoneural Junction

Abstract

Cross-striated muscles of frogs and rats were fixed in 3.3 per cent lead nitrate solution. Frozen sections 30 micra thick were mounted in different media and observed by polarization microscopy. The subneural apparatus of myoneural junctions exhibits a strong birefringence in these sections. Birefringence is exerted by a highly organized lipoprotein framework (postsynaptic material) which builds up the "organites" (iunctional folds) of the postsynaptic membrane. Synaptic cholinesterase is closely associated with this material. Freezing and/or formalin fixation results in a destruction of the molecular organization of the postsynaptic material, but does not influence the synaptic enzyme activity. It is hypothesized from this study that the junctional folds (postsynaptic "organites") consist of regularly arranged, sheet-like lamellar micellae in the frog and of less regular, mainly radially arranged submicroscopic units in the rat. The micellar organization as revealed by polarization analysis is in good agreement with the electron microscopic findings reported in the literature. Intramicellar protein molecules of the resting postsynaptic membrane are arranged longitudinally, lipids transversely. Supramaximal stimulation or treatment with acetylcholine q-eserine results in a disorganization of proteins and a rearrangement of lipids. Denervation results in a rearrangement of lipids without any significant alterations of proteins. All these functional stresses influence only the molecular and not the micellar structure of the membrane. The function of the organized lipoprotein framework as an acetylcholine receptor is suggested.

Palaeontological evidence for membrane fusion between a unit membrane and a half-unit membrane

“…(ii) This membrane fusion pattern also exists in recent plants but people simply have not observed it in recent plants yet. We favor the latter alternative because (i) the age of the fossil is 15 Á20 Ma, which appears too short for such a drastic variation to occur; and (ii) there have been, though rare, reports of half-unit membranes in recent plants (Hodge et al 1956, Csillik 1963, Cardell et al 1967, Anderson et al 1970, Yatsu et al 1971, Konar et al 1972, Yatsu & Jacks 1972, Gardner & Hess 1977, Hilhorst et al 1982, de Castro & MartinezHonduvilla 1984, Scherz et al 1990, Somerville et al 2002, Schumann et al 2003) and some of them contain secretory contents, and thus they (halfunit membranes) have to fuse with CM (unit membranes) somehow somewhere sooner or later. Theoretically, this type of membrane fusion is inevitable for plant cells.…”

“…Thus it is not surprising that almost all of the models of membrane fusion concern fusion between two unit membranes (Palade & Bruns 1968, Lucy 1970, Poole et al 1970, Thiel & Battey 1998, Blatt et al 1999, Blatt 2002, Tamm et al 2003, Tuma & Hubbard 2003, Jena 2005a&b, Chernomordik & Kozlov 2005, Wong et al 2007, Figure 4a). On the other hand, although half-unit membranes, composed of a monomolecular layer of radially-oriented phospholipid elements (Hodge et al 1956, Csillik 1963, Cardell et al 1967, Ambrose & Easty 1979, Hilhorst et al 1982, Scherz et al 1990, have been intensively studied by biochemists (Fromherz & Rü ppel 1985, Moscho et al 1996, Oliveira et al 1998, Brockman 1999, Deleu et al 2005, Rosetti et al 2005, in living cells they only rarely are reported (for example, mouse liver and muscle, mature cells and young apical cells of Nitella cristata, root tips of germinating wheat, and leaves of Zea mays, Hodge et al 1956;Rana esculenta and Mus rattus, Csillik 1963;rat, Cardell et al 1967;Triticum aestivum , Anderson et al 1970;Allium cepa, Brassica capitata, Gossypium hirsutum , Yatsu et al 1971;Ranunculus sceleratus , Konar et al 1972; Arachis hypogaea, Yatsu & Jacks 1972; Tilletia caries , Gardner & Hess 1977;Desulfovibrio vulgaris , Hilhorst et al 1982; Pinus pinea , de Castro & Martinez-Honduvilla 1984;Rhodospirillum rubrum , Scherz et al 1990; Zea...…”

“…On the other hand, although half-unit membranes, composed of a monomolecular layer of radially-oriented phospholipid elements (Hodge et al 1956, Csillik 1963, Cardell et al 1967, Ambrose & Easty 1979, Hilhorst et al 1982, Scherz et al 1990, have been intensively studied by biochemists (Fromherz & Rü ppel 1985, Moscho et al 1996, Oliveira et al 1998, Brockman 1999, Deleu et al 2005, Rosetti et al 2005, in living cells they only rarely are reported (for example, mouse liver and muscle, mature cells and young apical cells of Nitella cristata, root tips of germinating wheat, and leaves of Zea mays, Hodge et al 1956;Rana esculenta and Mus rattus, Csillik 1963;rat, Cardell et al 1967;Triticum aestivum , Anderson et al 1970;Allium cepa, Brassica capitata, Gossypium hirsutum , Yatsu et al 1971;Ranunculus sceleratus , Konar et al 1972; Arachis hypogaea, Yatsu & Jacks 1972; Tilletia caries , Gardner & Hess 1977;Desulfovibrio vulgaris , Hilhorst et al 1982; Pinus pinea , de Castro & Martinez-Honduvilla 1984;Rhodospirillum rubrum , Scherz et al 1990; Zea mays, Somerville et al 2002;Arabidopsis , Schumann et al 2003). It is believed that a half-unit membrane provides a good package for storage and transport of photoproducts, enzymes (Hodge et al 1956, Csillik 1963, Cardell et al 1967, Yatsu et al 1971, Yatsu & Jacks 1972, Hilhorst et al 1982, Scherz et al 1990, Somerville et al 2002, and hydrophobic drugs …”

“…Biological membranes, including vesicular ones, are all thought to have a double-layered structure (Kimball 1970, Ambrose & Easty 1979, Zheng 1996, Staehelin & Newcomb 2002, Chernomordik & Kozlov 2005 even though half-unit membranes have been reported several times in cells (Hodge et al 1956, Csillik 1963, Cardell et al 1967, Anderson et al 1970, Yatsu et al 1971, Konar et al 1972, Yatsu & Jacks 1972, Gardner & Hess 1977, Hilhorst et al 1982, de Castro & Martinez-Honduvilla 1984, Scherz et al 1990, Somerville et al 2002, Schumann et al 2003. Although vesicle trafficking is of essential importance for nearly all eukaryotic cells (Blatt et al 1999, Blatt 2002, Koumandou et al 2007) and several models and modifications have been proposed for the fusion between vesicle and cytoplasmic membranes (Thiel & Battey 1998, Blatt et al 1999, Battey et al 1999, Blatt 2002, Chernomordik & Kozlov 2005 Figure 4a), none mentions the fusion between a half-unit membrane and a cytoplasmic membrane (CM).…”

A Light and Electron Microscopic Histochemical Study on the Mechanism of Dfp‐induced Acute and Subacute Myopathy

“…It has been shown that prolonged depolarization of the sarcolemmal membrane results in an influx of Ca2+ into the muscle cell (Csillik, 1965;Evans, 1974;Miledi et al, 1977). In addition, the binding of acetylcholine to the acetylcholine receptor is also accompanied by liberation of Ca2+ (Chang & Neumann, 1976;Rubsamen et al, 1976).…”