FINE STRUCTURE OF CELL SURFACE SPECIALIZATIONS IN THE MATURING DUODENAL MUCOSA OF THE CHICK

Cell surfaces in the duodenal mucosa have been studied in maturing tissue of the chick from incubation until hatching. Changes in the distribution of mitoses in this tissue give an indication of its rate of maturation. This rate is paralleled in developmental changes in microvilli and junctional complexes. Concentration of mitotic figures towards the base of villous folds is gradual from day 9 to day 16, then rapid to day 19, after which the mature pattern is acquired. By day 11, microvilli appear in a regular pattern which does not alter through hatching. Their height remains the same to day 16 when it increases gradually to day 19, then very sharply. The angle formed between the microvilli and the cell surface increases gradually to day 16, giving evidence of advancing internal structure. Changes in cell adhesion also occur at day 16. Thereafter, following trypsin treatment cells are held together in patches by the tight junctions of the terminal bar, although the desmosomes are separated. The timing of these morphological changes is compared with that of alkaline phosphatase accumulation in this tissue as reported by Moog (13). Increase in the surface area of the microvilli parallels the increase in the activity of the enzyme.

DIFFUSION OF WEAK ACIDS ACROSS THE TOAD BLADDER. INFLUENCE OF PH ON NON-IONIC PERMEABILITY COEFFICIENTS

Studies have been carried out, using the toad bladder, to determine the influence of pH on the permeability coefficients (K_trans) of the non-ionic species of (a) a series of aliphatic acids ranging from propionic to octanoic and (b) the aromatic acids, benzoic and acetylsalicylic. The data demonstrate that as the acidity of the mucosal bathing solution is increased by changing pH from 6 to 4, the fluxes of propionic, butyric, and acetylsalicylic acids increase in direct proportion to the increase in the calculated non-ionic concentration; the permeability coefficients, therefore, remain constant. However, the fluxes of the six, seven, and eight carbon aliphatic acids and benzoic acid rise only slightly despite an almost tenfold increase in non-ionic concentration, the K_trans falling from approximately 20,000 x 10^-7 cm sec.^-1 at pH 6 to approximately 2500 x 10^-1 cm sec.^-1 at pH 4. It has been tentatively proposed that the common characteristic of the compounds exhibiting this anomalous behavior is their non-polarity and high degree of lipid solubility. Possible explanations for the differences observed between the more lipid-soluble and less lipid-soluble compounds have been considered.

THE EFFECT OF MUCOSAL AND SEROSAL SOLUTION CATIONS ON BIOELECTRIC PROPERTIES OF THE ISOLATED TOAD BLADDER

The spontaneous transtissue potential and the DC conductance of the isolated toad bladder were measured when the tissue was exposed to sulfate Ringer's solutions of modified ionic composition. Na(+) was replaced to varying extents by (C(2)H(5))(3)NH(+), (C(2)H(5))(4)N(+), Li(+), Cs(+), K(+), or Rb(+). Reversible and irreversible changes were observed. The reversible changes were consistent with equations derived from the Nernst-Planck diffusion equation, and gave the following functional description of the bladder: (a) the potential measurements were compatible with two membranes in series; (b) the mucosal surface was more permeable to Na(+) than to other monovalent cations; (c) the serosal surface was permeable to both K(+) and Na(+) but preferentially to K(+); (d) the rate of Na(+) diffusion across the mucosal membrane appeared to approach a maximum but two alternative interpretations are discussed; (e) the conductance data were consistent with the assumption of a constant concentration gradient for the penetrating ions within the membrane (Henderson's assumption) provided suitable hypotheses are made concerning the Na(+) distribution between the membrane surfaces and the bulk phases of the adjacent solutions; (f) the conductance and spontaneous potential data suggested that the mucosal membranes of a small fraction of the epithelial cells were more permeable than the mucosal membranes of the majority of these cells. The irreversible changes were almost entirely associated with cation substitution in the serosal solution. However, Li(+) produced an irreversible fall in voltage when added to either side of the tissue.

UREA TRANSPORT ACROSS DOG INTESTINAL MUCOSA IN VITRO

Mucosal membranes from the small intestine of the dog were stripped and mounted for study between two bathing fluids, as previously described. The relationship between urea and water transport, including uphill movement of urea in the direction of water flow, was that expected from a combination of bulk flow and diffusion. If sieving was present, it was minor. Results for downhill movement of D2O, the isotopic water treated as a solute, were comparable to those for urea.

MUCUS IN INTESTINAL CONTENTS OF GERMFREE RATS

The fecal excretion of total nitrogen and of total hexosamines has been determined in germfree and conventional rats. Germfree rats excreted more hexosamines than the conventional rats, while no difference in the nitrogen excretion was found. Infection of the germfree rats with a normal flora resulted in a temporarily increased excretion of hexosamines and nitrogen over a period of 2 to 3 days after which they reached the level of the conventional animals. The contents of the germfree cecum contained 65 to 137 mg of hexosamines and 57 to 127 mg of nitrogen as compared to 1.2 to 5.3 and 7.4 to 23 mg in conventional animals. The high figures for hexosamines were due to an increase in the total amount of contents in the cecum and to a fivefold increase in the concentration of hexosamine-containing material. Studies on the distribution of hexosamine-containing cecal contents between sediment and supernatant after centrifugation at 20,000 g for 2 hours demonstrated that 5 to 10 per cent of the hexosamines occurred in the sediment in the germfree rats, while 75 to 85 per cent was found in this fraction in the conventional rats. The soluble part of the cecal contents in germfree as well as in the conventional rats contained 70 per cent of hexosamines in molecules with a molecular weight above approximatively 100,000 as found by gel filtration experiments on sephadex gels. The higher weight of the germfree cecal wall was reflected in a high total amount of nitrogen and hexosamines. Isolated strains of bacteria capable of reducing the cecal size in vivo did not show any capacity to degrade the mucus in vitro in a test system, where a full intestinal flora was highly active.

"MELANOGENIC METAPLASIA" OF MUCOUS GLANDS

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INTRINSIC FACTOR-LIKE ACTIVITY IN EXTRACTS OF GUINEA PIG INTESTINE

Co57-labeled B12 tube fed to guinea pigs with normal human gastric juice has been found in both the supernatant and sediment of a saline extract of intestinal mucosa. The Co57-labeled material in the supernatant was excluded from Sephadex G-25, was not ultrafiltrable, and functioned as an intrinsic factor-B12-Co57 complex in an in vitro assay for intrinsic factor activity.

EFFLUX OF SODIUM FROM ISOLATED TOAD BLADDER

A method of simultaneously determining the rates of loss of Na24 across the mucosal and serosal surfaces of the isolated toad bladder is described. The addition of vasopressin to the serosal medium causes an abrupt increase in the efflux of Na24 across the mucosal boundary, with no significant change in the efflux across the serosal surface. Replacement of sodium in the mucosal medium with choline causes no change in the efflux of Na24 across either the mucosal or serosal surfaces. The results indicate that the stimulation of active transport of sodium across the bladder after vasopressin is the result solely of an increase in the permeability to sodium of the mucosal surface. Vasopressin does not act directly on the active transport step at the serosal surface. In addition, the saturation kinetics which describe the process of sodium entry at the mucosal boundary are not the result of an exchange diffusion process, and appear not to be due to a sodium-induced change in the permeability of this surface to sodium.

MULTIPLICATION OF BRUCELLA IN CULTURED LYMPHOID AND NONLYMPHOID CELLS

Richardson, Marvis (Michigan State University, East Lansing), and Jane N. Holt. Multiplication of Brucella in cultured lymphoid and nonlymphoid cells. J. Bacteriol. 88:1163-1168. 1964.-Growth curves were established for the multiplication of Brucella abortus in cultured bovine cells. The number of viable brucellae was determined by colony count after lysis of the parasitized tissue cells. It was found that the number of brucellae dropped during the first 3 to 6 hr. This was followed by intracellular growth. Brucellae multiplied in uterine mucosal and fetal skin cells at an exponential rate with a 4-hr generation time. In contrast, only limited multiplication occurred in spleen cell cultures, usually approaching the stationary phase by 20 to 30 hr. Preliminary results indicated an average generation time of 8 hr in calf spleen cells. Differences were apparent in the ability of spleen cells from individual calves to support intracellular growth. This suggests that a relationship may exist between the establishment of intracellular pathogens in vitro and the natural resistance of the animal. By the use of fluorescein-labeled antisera, some insight was gained into the fate of brucellae in lymphoid cells. Fluorescent antisera stained intact brucellae and also revealed soluble antigen in the cytoplasm of reticularlike cells.