Direct Measurement of Potential Difference across the Human Red Blood Cell Membrane

The electrical potential difference across the human red cell membrane has been measured directly. A biological amplifier with neutralized input capacity was used. Human red cells in modified Ringer solution were impaled individually with 3 M KCl-filled glass microelectrodes. Movements of the microelectrodes were effected by Leitz micromanipulators. Results showed a potential difference of -8.0 ± 0.21 (SEM) mv, the inside being negative with respect to the outside. This value is approximately that calculated by using the Nernst equation considering the intracellular and extracellular chloride concentrations.

As a control, similar measurements were made on nylon microcapsules containing hemoglobin. The measured potential of -0.52 ± 0.02 (SEM) mv, which agreed very well with the value calculated on the basis of Donnan equilibrium, was much smaller in magnitude as compared to the results for the red cell, and there was evidence of fixed charges on the microcapsule membrane. There was no evidence of this in the case of the red cell.

     

LIPOFUSCIN (AGING) PIGMENT GRANULES OF THE NEWBORN HUMAN LIVER

We have observed pigmented cytoplasmic granules, with the characteristic staining properties of lipofuscin (ceroid, "wear-and-tear") pigment, in newborn human liver. The pigment is found at the periphery of the lobule in hepatocytes and some bile ductular cells. It is acid-fast, PAS-positive after diastase digestion, slightly argyophilic and sudanophilic, and markedly Schmorl's- and peroxidase positive in paraffin sections. Difficult to see in sections stained with hematoxylin and eosin, the pigment can be detected in unstained sections. The granules also resemble lipofuscin found in adult tissues, in their ultra-structural and enzymatic properties. They are polymorphic, contain granular material of moderate and high electron opacity, and are delimited by a single membrane. Acid phosphatase and β-glucuronidase activities are visualized in the newborn granules, identifying them as lysosomes. The granules also contain copper and, to a much lesser extent, iron. The accumulation of lipofuscin pigment in lysosomes in many tissues correlates well with aging, and this process has been interpreted as a reflection of cellular degeneration or wear-and-tear. However, the presence of lipofuscin granules as a constant component of neonatal liver suggests that they are not a measure of cellular senescence.     

Dextran-induced Agglutination of Streptococcus mutans, and Its Potential Role in the Formation of Microbial Dental Plaques

Glucose-grown washed cells of streptococci similar to Streptococcus mutans, which contain cell-bound dextransucrase, have been observed to agglutinate upon the addition of high molecular weight dextran. Low molecular weight dextran or unrelated polysaccharides were ineffective. Agglutination also occurred upon addition of sucrose, which can be converted into dextran, but not with other mono- and disaccharides. Other bacteria, including species capable of synthesizing dextrans, were not observed to exhibit this phenomenon. Cells of S. mutans agglutinated upon addition of dextran over a wide pH range, but maximal sensitivity to dextran occurred at pH 8.5. At this pH, such cells can be used for a simple, specific, and exquisitely sensitive qualitative assay for high molecular weight dextran, for addition of 6 ng of dextran with a molecular weight of 2 x 10(6) (i.e., approximately three molecules per cell) caused detectable agglutination. High concentrations of glucose, levan, and dextran of molecular weight of 2 x 10(4) inhibited the reaction. Fluorescein-labeled cells of S. mutans were observed to adhere to dextran-containing plaques and dextran-treated teeth, suggesting that this phenomenon may be of importance in the formation of streptococcal dental plaques. The mechanism responsible for dextraninduced agglutination appears to involve the affinity of a receptor site, possibly dextransucrase, on the surface of several cells for common dextran molecules.     

Relationship Between Amino Sugars and Meat Microbial Quality

The amino sugar content of spoiling beef increased with the microbial count and appeared to be responsible for the increased hydration capacity of spoiled meats.     

Area-sampling Technique for Quantitative Pharyngeal Cultures

An area-sampling device for obtaining quantitative samples of the oropharyngeal bacterial flora is described and illustrative data are presented.     

Effect of Culture Medium Composition and pH on the Production of M Protein and Proteinase by Group A Streptococci

The effects of pH, yeast extract, and neopeptone on the production of extracellular proteinase and M protein by group A streptococci were studied with a type 1 strain capable of producing both M protein and proteinase. The strain DS 2036-66 grew moderately well in a semisynthetic broth. M protein was produced without adding peptides to the medium. When added to a medium with 1% glucose, yeast extract (0.1%) was found to stimulate both growth and proteinase formation. Limiting the glucose to 0.25% prevented a drop in pH below 6.7 and prevented proteinase formation. Although less growth occurred with limited glucose, M protein of high specific activity was produced with an actual increase in acid-extractable M protein during the stationary phase of growth. When the medium was buffered at pH 7.85 with tris(hydroxymethyl)aminomethane buffer, 0.5% neopeptone prevented proteinase formation. This was true even in the presence of 1% glucose and 0.1% yeast extract, which resulted in a fall in pH to about 4.8 by 48 hr. Growth was greater than in Todd Hewitt broth, but the specific activity of M protein was considerably less than that found in the medium with glucose limited to 0.25%. Neopeptone was found to have little direct action on crude streptococcal proteinase. Instead, the evidence suggested that neopeptone somehow prevents proteinase elaboration. Yeast extract, on the other hand, appears to stimulate proteinase elaboration. To prevent proteinase formation, neopeptone must be added early, during the logarithmic phase of growth or at the start. In contrast, when yeast extract was added as late as 24 hr, it resulted in the elaboration of extracellular proteinase and in the decline of M protein. When 38 M nontypable strains from the diagnostic laboratory were tested for proteinase activity under conditions similar to those used in the diagnostic laboratory, only six produced much proteinase.