DNA distribution of mast cell populations in growing rats

Summary The proliferation of rat peritoneal mast cells was examined under normal conditions in vivo. DNA content of individual mast cells was measured by cytofluorometry after staining with the bibenzimidazole dye Hoechst 33258. Diploid non mast cells from each rat were used as a biological standard, which resulted in small long-term variations in the method. The proportion of mast cells in the S+G2 region of the DNA distribution was about 4% for young rats (24 days old, body-weights about 60 g). It decreased in relation to body-weight, and was less than 1% for 105-day-old rats weighing 400 g. During the same growth period the total number of mast cells in the peritoneal cavity increased about 8-fold. The total number of proliferating cells, about 30,000, remained constant throughout the observation period. No evidence of polyploidization or accumulation in G2 of mast cell nuclei was found. It is concluded that peritoneal mast cells increase in number by mitotic proliferation of differentiated cells.Supported by grants from the Swedish Medical Research Council, Project No. 2235     

Population of the diaphragm by mast cells in growing rats

The mast cell content of the diaphragm of the rat was examined using electron microscopy, and using light microscopy in material stained with Alcian blue. The concentration and diameters of the mast cells were estimated in animals at regular time intervals from 16 days gestation to 14 weeks of age and compared to the mast cell content of muscles of the calf and anterior abdominal wall. The results were discussed in relation to the origin of mast cells. It was proposed that if mast cells develop in haemopoietic sites that they may populate adjacent tissues by migrating within the connective-tissue spaces.     

Transport theory for growing cell populations

The partial differential equation that describes the growth of cell populations whose maturation rate is random is developed. The equation resembles that used in classical transport theory but mitotic boundary conditions and the restriction of the maturation rate to non-negative values brings out new features and new problems. This is a generalization of a previously published formulation in which cells could make transitions at random between only two maturation velocities: a characteristic velocity and zero. Growth rates, cycle time distributions and pulsed labeled mitotic curves are calculated for a simple choice of parameters. A numerical algorithm that is suited to the solution of the transport equation is given.     

Lectin histochemistry of the mast cell: Heterogeneity of rodent and human mast cell populations

Summary Mast cell granules contain a variety of N-linked saccharides. Heterogeneity of the expression of these saccharides in mast cells was studied in rodent and human tissues which were so selected as to contain all the mast cell subsets previously identified using other criteria. Dermal and intestinal mucosal mast cells were stained with lectins using an avidin-biotin system. It was found that dermal and subepidermal mast cells in the rat and mouse, and mucosal and dermal human mast cells showed very similar lectin binding properties to each other, with a fine variation in the inlensity of staining with certain lectins. Rat mucosal mast cells, however, showed a distinctive pattern of lectin binding which was not seen in mast cells from any other tissue studied. The chemical basis of the differences seen were deduced and the possible significance of these structural variations is discussed.     

A Fokker-Planck equation for growing cell populations

Closed form solutions are obtained for a Fokker-Planck model for cell growth as a function of maturation velocity and degree of maturation. For reproduction rules where daughter cells inherit their parent's maturation velocity the complete solution is derived in terms of Airy functions. For more complicated reproduction rules partial results are obtained. Emphasis is given to the relationship of these problems to time dependent linear transport theory.     

Histamine content of peritoneal and tissue mast cells of growing rats

Summary p-Phenylenediamine/pyrocatechol mixture (PPD-PC) was evaluated as a reagent for the ultracytochemical demonstration of retrograde axonal transport of horseradish peroxidase (HRP). HRP crystals were applied to the proximal stumps of the severed infraorbital nerves in rats. After 48 h the rats were sacrificed by perfusion, and the trigeminal ganglia ipsilateral to the severed nerves were processed for HRP cytochemistry and then prepared for electron microscopy. PPD-PC was rapidly oxidized in HRP-labeled neurons to form a dark brown-black osmiophilic reaction product which was more readily visible than the DAB product in the sections. This facilitated selection by light microscopy of areas in the epoxy wafers for ultrathin sectioning. In thin sections viewed under the electron microscope, the osmicated electron opaque PPD-PC reaction product was present in membrane-bound structures including smooth endoplasmic reticulum and granules of various sizes. The PPD-PC reaction product formed after 10-min incubation appeared to be more electron opaque than the DAB reaction product formed after 20 min. PPD-PC was found to be much less readily oxidized than DAB by endogenous hemoproteins. This methodology facilitated the ultracytochemical localization of HRP in neurons following retrograde axonal transport.Supported by NIH Grants DE 04730, DE 02668 and DE 00288 from the National Institute for Dental Research, NIH Grant RR 0533 from the Division of Research Facilities and Resources, and a grant to the Neurobiology Program from the Alfred P. Sloan Foundation     

Delayed mast cell mediated mitogenic reactivity in diabetic rats

Rats with diabetes of 4 weeks' duration have previously demonstrated increased mitogenesis in normal connective tissue cells following mast cell secretion. The appearance of this augmented mast cell-mediated mitogenic reactivity was studied in the mesentery of insulin-deficient rats, 3, 7, and 28 days after they had been rendered diabetic by a single dose of streptozotocin. On day 7 mast cell secretion induced a subnormal mitogenic response which, however, increased above normal on day 28. This time lag in the augmentation of mitogenic responsiveness may be important since proliferative lesions in diverse mesenchymal tissues typically develop with a similar delay in both experimental and clinical diabetes.     

Synchronized oscillations in growing cell populations are explained by demographic noise

Understanding synchrony in growing populations is important for applications as diverse as epidemiology and cancer treatment. Recent experiments employing fluorescent reporters in melanoma cell lines have uncovered growing subpopulations exhibiting sustained oscillations, with nearby cells appearing to synchronize their cycles. In this study, we demonstrate that the behavior observed is consistent with long-lasting transient phenomenon initiated and amplified by the finite-sample effects and demographic noise. We present a novel mathematical analysis of a multistage model of cell growth, which accurately reproduces the synchronized oscillations. As part of the analysis, we elucidate the transient and asymptotic phases of the dynamics and derive an analytical formula to quantify the effect of demographic noise in the appearance of the oscillations. The implications of these findings are broad, such as providing insight into experimental protocols that are used to study the growth of asynchronous populations and, in particular, those investigations relating to anticancer drug discovery.     

Abolishment of TNBS-induced visceral hypersensitivity in mast cell deficient rats

Mucosal mast cells are implicated in visceral hypersensitivity associated with irritable bowel syndrome (IBS). In this study, we investigated the role of mast cells in the development of visceral hypersensitivity by using mast cell deficient (Ws/Ws) rats and their control (W+/W+). In W+/W+ rats, an injection of 2,4,6-trinitrobenzene sulfonic acid (TNBS) into the proximal colon produced a significant decrease in pain threshold of the distal colon. Severe mucosal necrosis and inflammatory cell infiltration with concomitant increase in tissue myeloperoxidase activity were observed in the proximal colon that was directly insulted by TNBS, whereas neither necrosis nor increased myeloperoxidase activity occurred in the distal colon, indicating that TNBS-induced hypersensitivity is not caused by the local tissue damage or inflammation in the region of the gut where distention stimuli were applied. On the other hand, TNBS failed to elicit visceral hypersensitivity in Ws/Ws rats. This finding indicates that mast cells are essential for development of TNBS-induced visceral hypersensitivity in rats. Since the severity of TNBS-induced proximal colon injury and MPO activity was not affected by mast cell deficiency, it is unlikely that abolishment of visceral hypersensitivity in mast cell deficient rats was a result of altered development of the primary injury in the proximal colon. There was no difference between sham-operated Ws/Ws and W+/W+ rats in colonic pain threshold to distention stimuli, indicating that mast cells play no modulatory roles in normal colonic nociception. The present results support the view that mucosal mast cells play key roles in the pathogenesis of IBS.     

Individual-based and continuum models of growing cell populations: a comparison

In this paper we compare two alternative theoretical approaches for simulating the growth of cell aggregates in vitro: individual cell (agent)-based models and continuum models. We show by a quantitative analysis of both a biophysical agent-based and a continuum mechanical model that for densely packed aggregates the expansion of the cell population is dominated by cell proliferation controlled by mechanical stress. The biophysical agent-based model introduced earlier (Drasdo and Hoehme in Phys Biol 2:133-147, 2005) approximates each cell as an isotropic, homogeneous, elastic, spherical object parameterised by measurable biophysical and cell-biological quantities and has been shown by comparison to experimental findings to explain the growth patterns of dense monolayers and multicellular spheroids. Both models exhibit the same growth kinetics, with initial exponential growth of the population size and aggregate diameter followed by linear growth of the diameter and power-law growth of the cell population size. Very sparse monolayers can be explained by a very small or absent cell-cell adhesion and large random cell migration. In this case the expansion speed is not controlled by mechanical stress but by random cell migration and can be modelled by the Fisher-Kolmogorov-Petrovskii-Piskounov (FKPP) reaction-diffusion equation. The growth kinetics differs from that of densely packed aggregates in that the initial spread, as quantified by the radius of gyration, is diffusive. Since simulations of the lattice-free agent-based model in the case of very large random migration are too long to be practical, lattice-based cellular automaton (CA) models have to be used for a quantitative analysis of sparse monolayers. Analysis of these dense monolayers leads to the identification of a critical parameter of the CA model so that eventually a hierarchy of three model types (a detailed biophysical lattice-free model, a rule-based cellular automaton and a continuum approach) emerge which yield the same growth pattern for dense and sparse cell aggregates.     

Amino acid uptake in growing and arrested human diploid cell populations.

Human diploid fibroblasts cultured in vitro weremonitored for amino acid uptake in preconfluent and confluent cultures under conditions amenable to growth and in confluent cultures arrested in an essentially nonmitotic state. Preconfluent and confluent cultures in growth medium showed similar uptake patterns for leucine and alpha-aminoisobutyrate; arrested cultures exhibited a reduced uptake of both amino acids. Kinetic measurements revealed a 4-fold reduction in apparent Vmax for alpha-aminoisobutyrate influx in arrested cultures. These results suggest that the culture conditions used in this study to produce restrictions in mitotic activity likewise influence amino acid accumulation.