Visualization at the mouse neuromuscular junction of a submembrane structure in common with Torpedo postsynaptic membranes

To test for submembrane structures common to postsynaptic membranes of muscle and electric tissue, mouse sternomastoid muscles were fixed in the presence of tannic acid under conditions such that a heavy layer of densely staining material was built up on plasma membranes. In this section electron micrographs of such muscles, the hydrophobic portion of the bilayer and some membrane-associated structures appear in strong negative contrast. At the endplate, acetylcholine receptor-rich membrane regions appear as a broad (14-15-nm) image approximately bisected by the thin (approximately 2-nm) image of the bilayer. The extracellular half of the image arises from the receptor protein. The cytoplasmic half contains a distinct bar of contrasted material which is precisely co-extensive with the receptor image Quantitative and direct visual comparisons show that the image is almost indistinguishable from that obtained by a similar method applied to isolated postsynaptic membranes from electric tissue of Torpedo californica (Sealock, R. (1982) J. Cell Biol. 92:514-522). In the latter case, the bar probably arises from the 43,000-dalton protein, a major peripheral membrane protein component of the isolated membranes. The results thus suggest that the 43,000-dalton protein in muscle and electric tissue forms similar structures and, conversely, that the structure in the isolated membranes retains the essential features of its in situ state

y scaling in electron-nucleus scattering

Data on inclusive electron scattering from A = 4, 12, 27, 56, 197 nuclei at large momentum transfer are presented and analyzed in terms of y scaling. We find that the data do scale for y 1), and we study the convergence of the scaling function with the momentum transfer Q^2 and A

Ultrastructural localization of the Mr 43,000 protein and the acetylcholine receptor in Torpedo postsynaptic membranes using monoclonal antibodies

Four mouse monoclonal antibodies (mabs) were shown by immunoblotting procedures to recognize the major, basic, membrane-bound Mr 43,000 protein (43K protein) of acetylcholine receptor-rich postsynaptic membranes from Torpedo nobiliana . These mabs and a mab against an extracellular determinant on the acetylcholine receptor were used to localize the two proteins in electroplax (Torpedo californica) and on unsealed postsynaptic membrane fragments at the ultrastructural level. Bound mabs were revealed with a rabbit anti-mouse Ig serum and protein A-colloidal gold. The anti-43K mabs bound only to the cytoplasmic surface of the postsynaptic membrane. The distributions of the receptor and the 43K protein along the membrane were found to be coextensive. Distances between the membrane center and gold particles were very similar for anti-receptor and anti-43K mabs (29 +/- 7 nm and 26 to 29 +/- 7 to 10 nm, respectively). These results show that the 43K protein is a receptor-specific protein having a restricted spatial relationship to the membrane. They thus support models in which the 43K protein is associated with the cytoplasmic domains of the receptor molecule

Relationship between Body Composition and Reproduction in Heifers

Carcass and reproductive data including scan weight, ribeye area, rump fat, 12-13th rib fat and percentage intramuscular fat and reproductive tract scores (RTS) at 344 days were collected on 180 1998-born and 70 1999-born Angus heifers to determine the relationship between these traits. 1998-born heifers with higher RTS tended to be heavier and have more rump fat at 405 days (P \u3c .05). Heavier heifers and heifers with more rump fat had higher RTS when adjusted to 395 days (P \u3c .05). 1999-born heifers showed a similar pattern, with heavier heifers having higher RTS (P \u3c .05). Rump fat was not as significant for 1999-born heifers compared with 1998-born heifers. Heavier heifers with more rump fat are more likely to have more mature reproductive tracts at breeding

The 30 S lobster skeletal muscle Ca2+ release channel (ryanodine receptor) has functional properties distinct from the mammalian channel proteins.

The 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps)-solubilized ryanodine receptor (RyR) of lobster skeletal muscle has been isolated by rate density centrifugation as a 30 S protein complex. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified 30 S receptor revealed a single high molecular weight protein band with a mobility intermediate between those of the mammalian skeletal and cardiac M(r) 565,000 RyR polypeptides. Immunoblot analysis showed no or only minimal cross-reactivity with the rabbit skeletal and canine cardiac RyR polypeptides. By immunofluorescence the lobster RyR was localized to the junctions of the A-I bands. Following planar lipid bilayer reconstitution of the purified 30 S lobster RyR, single channel K+ and Ca2+ currents were observed which were modified by ryanodine and optimally activated by millimolar concentrations of cis (cytoplasmic) Ca2+. Vesicle-45Ca2+ flux measurements also indicated an optimal activation of the lobster Ca2+ channel by millimolar Ca2+, whereas 45Ca2+ efflux from mammalian skeletal and cardiac muscle sarcoplasmic reticulum (SR) vesicles is optimally activated by micromolar Ca2+. Further, mammalian muscle SR Ca2+ release activity is modulated by Mg2+ and ATP, whereas neither ligand appreciably affected 45Ca2+ efflux from lobster SR vesicles. These results suggested that lobster and mammalian muscle express immunologically and functionally distinct SR Ca2+ release channel protein complexes

Association of Utrophin and Multiple Dystrophin Short Forms with the Mammalian Mr 58,000 Dystrophin-associated Protein (Syntrophin)

Electric tissue syntrophin, originally described as an M(r) 58,000 postsynaptic protein having homologs in mammalian muscle, was previously shown to associate with dystrophin in Triton extracts of Torpedo postsynaptic membranes. It also associates with the Torpedo M(r) 87,000 postsynaptic protein (87K), the core of which is a superdomain homologous to the cysteine-rich (CR) and COOH-terminal (CT) domains of human dystrophin. Using immunoaffinity purifications from various rat tissues and immunoblotting, we find that syntrophin associates with dystrophin, utrophin (the chromosome 6-encoded dystrophin homolog formerly known as dystrophin-related protein), multiple proteins which are cross-reactive with 87K, and two subfamilies of 71K-like proteins (CRCT-containing proteins encoded by the dystrophin gene under the control of an alternative promoter in intron 62). One 71K subfamily retains the dystrophin COOH-terminal sequence; the other has an alternative COOH-terminal sequence caused by deletion of the penultimate exon by alternative splicing. The relative masses of the members of the subfamilies suggest they arise by alternative splicing at other previously described sites within CT. These results establish that syntrophin is a general ligand for the CRCT domain in mammalian dystrophin and its homologs. They also reveal a greater diversity in 71K proteins than has previously been apparent