The effect of low ionic strength extracellular solutions on the resting potential in skeletal muscle fibers

Intracellular measurements of the resting potential were made in fibers of the frog sartorius muscle in solutions of varying salt composition and concentration to determine the effects of low ionic strength extracellular solutions on the resting potential. Changes in the glass microelectrode tip potential in low ionic strength solutions were minimized by adding ThCl₄ to the extracellular solution. These experimental conditions allowed measurement of the relationship of the resting potential to the concentration of the salt in the extracellular solution by replacing it with the nonionic substance, sucrose. Substitution of sucrose for the extracellular NaCl produced a stable depolarization which was logarithmically related to the NaCl concentration. Substitution of sucrose for choline Cl, instead of NaCl, produced the same degree of depolarization. When Na salts of anions less permeable than chloride (Br, I, NO₃) were used, the resting potentials in 116 mM solutions were close to those with chloride (±3mv). The depolarizations produced in low ionic strength solutions of these salts were significantly less than those with chloride.     

Mycoside G, a Specific Glycolipid in Mycobacterium marinum (Balnei).

Navalkar, R. G. (University of Wisconsin, Madison), E. Wiegeshaus, E. Kondo, H. K. Kim, and D. W. Smith. Mycoside G, a specific glycolipid in Mycobacterium marinum (Balnei). J. Bacteriol. 90:262-265. 1965.-A new specific glycolipid in extracts prepared from strains designated Mycobacterium marinum and M. balnei has been demonstrated by use of the techniques of column chromatography and infrared spectroscopy. Since there is now agreement among many workers that M. marinum and M. balnei are identical, the demonstration of the same specific glycolipid in both species is not surprising. This substance, which we have designated mycoside G, is chemically similar to mycosides A and B, and apparently differs only in the sugar moiety. In addition, the lipids extracted from these cultures contain phthiocerol dimycocerosate, a wax component found also in M. tuberculosis and M. bovis.     

LYSOSOMES IN THE RAT SCIATIC NERVE FOLLOWING CRUSH

Peripheral nerves undergoing degeneration are favorable material for studying the types, origins, and functions of lysosomes. The following lysosomes are described: (a) Autophagic vacuoles in altered Schwann cells. Within these vacuoles the myelin and much of the axoplasm which it encloses in the normal nerve are degraded (Wallerian degeneration). The delimiting membranes of the vacuoles apparently form from myelin lamellae. Considered as possible sources of their acid phosphatase are Golgi vesicles (primary lysosomes), lysosomes of the dense body type, and the endoplasmic reticulum which lies close to the vacuoles. (b) Membranous bodies that accumulate focally in myelinated fibers in a zone extending 2 to 3 mm distal to the crush. These appear to arise from the endoplasmic reticulum in which demonstrable acid phosphatase activity increases markedly within 2 hours after the nerve is crushed. (c) Autophagic vacuoles in the axoplasm of fibers proximal to the crush. The breakdown of organelles within these vacuoles may have significance for the reorganization of the axoplasm preparatory to regeneration. (d) Phagocytic vacuoles of altered Schwann cells. As myelin degeneration begins, some axoplasm is exposed. This is apparently engulfed by the filopodia of the Schwann cells, and degraded within the phagocytic vacuoles thus formed. (e) Multivesicular bodies in the axoplasm of myelinated fibers. These are generally seen near the nodes of Ranvier.     

In vitro capacitation and fertilizing ability of ejaculated rabbit sperm treated with lysophosphatidylcholine

Four experiments were replicated 1) to establish dose-response relationships between lysophosphatidylcholine (LPC), sperm motility, and the acrosome reaction (AR), 2) to evaluate the influence of rabbit serum (RS) on these endpoints, 3) to compare buck differences in induction of the AR, and 4) to examine fertilizing ability in vitro of sperm tested under the first three objectives. Semen was collected from Dutch-belted rabbits, washed once by centrifugation, resuspended, and preincubated for 2 or 4 hr in a chemically defined medium (DM), DM plus 20% RS, or BSA-free DM plus 20% RS at 37°C. At the end of preincubation LPC was added to the preincubated sperm at concentrations of from 0 to 100 μg/ml. Sperm were examined .5–4 hr later for AR and sperm motility. For in vitro fertilization, sperm and ova were coincubated in DM up to 24 hr after insemination and in a more complex medium for another 24 hr. Addition of LPC to 4-hr-preincubated sperm was more effective for inducing the AR than addition to 2-hr-preincubated sperm. A significant increase (P < .05) in the AR occurred in 15 and 30 min following exposure to 100 and 80 μg of LPC per ml, respectively, but the higher concentration of LPC decreased sperm motility. Addition of 20% RS to DM with or without BSA surprisingly inhibited the AR but maintained sperm motility, as expected. Bucks differed (P < .05) in the initial percentage and the induced percentage of AR sperm. For the AR the optimal concentration of LPC per ml was 80 μg, but for in vitro fertilization 60 μg tended to be superior.     

Hydrophilic solute transport across rat alveolar epithelium

Diffusional fluxes of a series of hydrophilic nonelectrolytes (molecular radii ranging from 0.15 to 0.57 nm) were measured across the alveolocapillary barrier in the isolated perfused fluid-filled rat lung. Radiolabeled solutes were lavaged into the distal air spaces of isolated Ringer-perfused lungs, and apparent permeability-surface area products were calculated from the rates of isotope appearance in the recirculating perfusate. These data were used to estimate theoretical equivalent pore radii in the alveolar epithelium, with the assumption of diffusive flow through water-filled cylindrical pores. The alveolar epithelium is best characterized by two pore populations, with small pores (radius 0.5 nm) occupying 98.7% of total pore area and larger pores (radius 3.4 nm) occupying 1.3% of total pore area. Net water flow out of the alveolar space was measured by including an impermeant solute (dextran) in the lavage fluid and measuring its concentration in the alveolar space as a function of time. Under control conditions, net water flow averaged 167 nl/s. When 24 microM terbutaline was added to the perfusate, net water flow increased significantly to 350 nl/s (P less than 0.001). Terbutaline had no effect on the fluxes of either glycerol (which traverses the small pore pathway) or sucrose (which traverses the large pore pathway). These findings indicate that the intact mammalian alveolar epithelium is complex and highly resistant to the flow of solutes and water.     

Properties,synthesis, and accumulation of storage proteins in Pieris rapae L.

Two kinds of storage proteins (SP-1, SP-2) were confirmed in hemolymph and fat body of Pieris rapae during metamorphosis. Both proteins were present in high concentrations in the hemolymph during the last larval instar. Hemolymph concentrations of SP-1 and SP-2 dropped after pupation as the proteins were being deposited in fat bodies. SP-2 is present in a larger amount than SP-1. Detailed studies on storage proteins determined their properties, mode of synthesis, and accumulation in the fat body. SP-1 has a molecular weight of 500,000 and consists of one type of subunit (M_r 77,000), while SP-2 has a molecular weight of 460,000 and is composed of two types of subunits (M_r 80,000 and 69,000). The pl values of SP-1 and SP-2 were determined to be 6.97 and 7.06, respectively. Fat body cells from 1-day-old fifth instar larvae synthesized storage proteins in large amounts, whereas those from late prepupae exhibited high protein sequestration. Proteins taken up in fat body accumulated in dense granules during the pupal stage but sharply decreased at the adult stage. Morphological changes in the fat body tissues were observed during the larval-pupal transformation; the nuclei of fat body cells became irregularly shaped, and the boundaries between cells seemed to be obscure. Synthesis, storage, or degradation of storage proteins in fat body during development is closely associated with morphological changes in the tissues.     

The influence of creosote compounds on the aerobic degradation of toluene

The inhibiting effect of 14 typical creosote compounds on the aerobic degradation of toluene was studied in batch experiments. Four NSO-compounds (pyrrole, 1-methylpyrrole, thiophene, and benzofuran) strongly inhibited the degradation of toluene. When the NSO-compounds were present together with toluene, little or no degradation of toluene was observed during 16 days of incubation, compared with a total removal of toluene within 4 days when the four compounds were absent. Indole (an N-compound) and three phenolic compounds (phenol, o-cresol, and 2,4-dimethylphenol) also inhibited the degradation of toluene, though the effect was much weaker that of the four NSO-compounds. O-xylene, p-xylene, naphthalene and 1-methylnaphthalene seemed to stimulate the degradation even though the influence was very weak. No effects of benzothiophene (an S-compound) and quinoline (an N-compound) were observed. Benzofuran (an O-compound) was identified as the compound that most inhibited the degradation of toluene. An effect could be detected even at low concentrations (40 g/l).Abbreviations bf benzofuran - bt benzothiophene - dmp 2,4-dimethylphenol - GC gas chromatograph - ind indole - mnap 1-methylnaphthalene - MAH monoaromatic hydrocarbons - mpyr 1-methylpyrrole - nap naphthalene - o-cre o-cresol - o-xyl o-xylene - phe phenol - pyr pyrrole - p-xyl p-xylene - tol toluene - thi thiophene - qui quinoline     

Transforming growth factor beta 1 increases IgA isotype switching at the clonal level

Transforming growth factor beta 1 (TGF beta 1) has important effects on expression of the IgA isotype. TGF beta 1 alone, or in combination with IL-5 or IL-2 increases IgA secretion by populations of LPS-activated surface IgA negative (sIgA-) spleen B cells, while concurrently decreasing IgM and IgG secretion. The present study demonstrates the activity of TGF beta 1 as an IgA isotype switch factor at the clonal level. Stimulation of LPS-activated sIgA- spleen B cell populations with TGF beta 1, or a combination of TGF beta 1 and IL-2, resulted in a significant increase in total numbers of IgA secreting cells, and this increase ultimately was paralleled by an increase in total IgA secretion. Using limiting dilution analysis, TGF beta 1 was shown to increase the frequency of IgA secreting B cell clones, by approximately 20-fold. This was not accompanied by increased numbers of IgA secreting cells/clone. In contrast, IL-2 does not have activity as an IgA switch factor, but does increase IgA production by B cells already committed to secrete that isotype. Cell cycle inhibitors such as thymidine and hydroxyurea also selectively increased numbers of IgA secreting cells and total IgA secretion among populations of LPS-activated sIgA- spleen B cells. This suggests the IgA enhancing activity of TGF beta 1 may, in part, be related to its ability to inhibit cell growth.