The role of calcium and magnesium-ATP on the structure and contractility in motile extracts of Amoeba proteus and plasmalemma-ectoplasm "ghosts" of Chaos carolinensis has been investigated by correlating light and electron microscope observations with turbidity and birefringence measurements. The extract is nonmotile and contains very few F-actin filaments and myosin aggregates when prepared in the presence of both low calcium ion and ATP concentrations at an ionic strength of I = 0.05, pH 6.8. The addition of 1.0 mM magnesium chloride, 1.0 mM ATP, in the presence of a low calcium ion concentration (relaxation solution) induced the formation of some fibrous bundles of actin without contracting, whereas the addition of a micromolar concentration of calcium in addition to 1.0 mM magnesium-ATP (contraction solution) (Taylor, D. L., J. S. Condeelis, P. L. Moore, and R. D. Allen. 1973. J. Cell Biol. 59:378-394) initiated the formation of large arrays of F-actin filaments followed by contractions. Furthermore, plasmalemma-ectoplasm ghosts prepared in the relaxation solution exhibited very few straight F-actin filaments and myosin aggregates. In contrast, plasmalemma-ectoplasm ghosts treated with the contraction solution contained many straight F-actin filaments and myosin aggregates. The increase in the structure of ameba cytoplasm at the endoplasm-ectoplasm interface can be explained by a combination of the transformation of actin from a less filamentous to a more structured filamentous state possibly involving the cross-linking of actin to form fibrillar arrays (see above-mentioned reference) followed by contractions of the actin and myosin along an undetermined distance of the endoplasm and/or ectoplasm.Experimental motile model systems have played a significant role in understanding the structural and chemical dynamics of cell movements. Simard-Duquesne and Couillard (31) elicited visible contractions in glycerinated models of Amoeba proteus upon the addition of magnesium and ATP. Cytoplasmic contractions and streaming have been identified both in cytoplasm removed from the plasmalemma (l, 12, 33) and in fractionated cytoplasm (39,46,27). In addition, it has been shown that cytoplasm isolated from single specimens of Chaos carolinensis contracted upon the addition of at least 7.0 • l0 -7 M free calcium ions in the presence of an endogenous magnesium-ATP

The triangularis sterni (TS) is an expiratory muscle that is passively stretched during inspiration. The magnitude of passive stretch depends upon the location of individual fibers within the TS muscle, with fibers located more caudally being stretched $ 5% to 10% more than fibers in the cephalad region. In the mdx mouse model for muscular dystrophy, the TS exhibits severe pathological alterations that are ameliorated by treatment with inhibitors of the NF-jB pathway. The purpose of this study was to assess the influence of passive stretch in vivo on fiber morphology in nondystrophic and mdx TS muscles, and the morphological benefits of treating mdx mice with two distinct NF-jB inhibitors, pyrrolidine dithiocarbamate (PDTC), and ursodeoxycholic acid (UDCA). Transmission electron microscopy revealed Z-line streaming, hypercontraction, and disassociation of the plasma membrane from the basal lamina in mdx fibers. In both nondystrophic and mdx TS muscles, fiber density was larger in more caudal regions. In comparison with nondystrophic TS, fibers in the mdx TS exhibited substantial reductions in diameter throughout all regions. In vivo treatment with either PDTC or UDCA tended to increase fiber diameter in the middle and decrease fiber diameter in the caudal TS, while reducing centronucleation in the middle region. These results suggest that passive stretch induces hypercontraction and plasma membrane abnormalities in dystrophic muscle, and that differences in the magnitude of passive stretch may influence fiber morphology and the actions of NF-jB inhibitors on dystrophic morphology. Anat Rec, 294:132-144, 2011. V V C 2010 Wiley-Liss, Inc.

Tamm-Horsfall protein (THP), a monomeric glycoprotein (M(r) 80 to 100 kDa), is produced by the mammalian kidney's thick ascending limb of Henle cells and excreted into the urine. The function of THP is uncertain. Here we report that a high molecular weight contaminant in sheep THP (sTHP) preparations was identified as sheep IgG by its positive reaction with donkey anti-sheep IgG antibody and with protein G. To answer the question of whether sTHP and sheep IgG co-purified because of a physical interaction between the two proteins, an enzyme-linked immunosorbent assay (ELISA) using immobilized sTHP and soluble sheep IgG was performed. Analysis of the ELISA data identified the presence of two sets of binding sites: a high affinity site (Kd 10(-8) to 10(-9) M) and a lower affinity site (Kd 10(-6) to 10(-7) M) [corrected]. The ELISA detected a similar high affinity interaction between human THP (hTHP) and human IgG. The binding of sheep IgG to immobilized sTHP was inhibited by soluble sTHP. These observations suggest an additional factor to be considered in studies addressing THP's potential immunoregulatory function.

Transforming growth factor a (TGF-a), a protein secreted by transformed cells and related to epidermal growth factor (EGF), was tested for its effects on gastric acid secretion. Guinea pig gastric mucosae were mounted in Ussing chambers and the rate of acid release was monitored by the pH-stat method. When administered prior to the secretagogue, TGF-a prevented the histamine-induced increase in the rate of acid secretion. Similarly, TGF-a caused a decrease in the rate of acid release in tissues that had already been stimulated with histamine. These data show that TGF-a inhibits gastric acid secretion in a manner similar to EGF and that the two growth factors share at least one physiological action unrelated to their mitogenic properties.Transforming growth factor a (TGF-a) is a protein that is structurally and functionally similar to epidermal growth factor (EGF). The overall amino acid sequences of these two peptides are about 33% homologous, and there is an even more highly conserved core region (1-4). TGF-a competes with EGF for binding to a receptor on the surface of cultured cells and isolated membranes (5-10), and an antibody to the EGF receptor blocks the mitogenic activity of conditioned medium containing TGF-a (11). TGF-a (or a partially purified preparation containing TGF-a) stimulates phosphorylation of tyrosine residues on the EGF receptor and other substrates (9, 12, 13). TGF-a, like EGF, is mitogenic for cultured cells (5,9,14) and in conjunction with transforming growth factor f3 permits anchorage-independent growth of NRK cells (7-10). In vivo, both TGF-a and EGF cause precocious separation of eyelids of newborn mice (15,16).In addition to these growth-related phenomena, EGF is known to inhibit gastric acid secretion (17-22). We have previously (22) used an Ussing-chamber preparation of guinea pig mucosae to study EGF's antisecretory properties. This system has the advantages over whole-animal models that the concentrations oftest substances can be precisely controlled, that secondary effects arising from interaction of the test substances with other organs are eliminated, and that much smaller quantities of reagents are required. These properties make the in vitro guinea pig model ideal for studying the effects of peptides related to EGF.One possible explanation for the coexistence of EGF and TGF-a is that, besides their shared mitogenic properties, they might also have biological activities unique to each peptide. To determine whether inhibition of acid secretion is one of these unique properties, we examined the effect of TGF-a on the Ussing-chamber preparation of guinea pig mucosa. We report here that TGF-a is capable of inhibiting histaminestimulated acid secretion in a manner similar to EGF. MATERIALS AND METHODSStomachs from young (200-to 250-g) female guinea pigs were hemisected along the greater and lesser curvatures and placed mucosal-surface down on a piece of Parafilm. The outer muscle layers were removed with fine forceps and both halves of the mucosa were mounted separately ...

No abstract