Biomedical subjects

T P Shearer

Publications and source records attributed to T P Shearer.

4 recordsLinked to original sources

PubMed1999

Analysis of aryl hydrocarbon receptor-mediated signaling during physiological hypoxia reveals lack of competition for the aryl hydrocarbon nuclear translocator transcription factor.

The aryl hydrocarbon nuclear translocator (ARNT) protein functions as a transcription factor after dimerization with other basic helix-loop-helix proteins. Thus, dimerization of ARNT within one pathway may limit the availability of this protein to others. To investigate this issue, aryl hydrocarbon receptor (AHR)-mediated signaling was investigated in mouse (Hepa-1), rat (H4IIE), and human (HepG2) hepatoma cell lines undergoing physiologically induced hypoxia (<1% O(2)). Basal levels of ARNT protein were not affected by hypoxia in any cell line, and ARNT remained exclusively nuclear. Furthermore, quantitative Western blotting revealed that the concentration of ARNT sequestered during hypoxia represented a small fraction of the total ARNT protein pool (12 and 15% in Hepa-1 and H4 cells, respectively). When the AHR-mediated signaling pathway was activated during hypoxia by 2,3,7,8-tetrachlorodibenzo-p-dioxin, the induction of P4501A1 protein was reduced by 55% without changes in the level of mRNA in Hepa-1 cells, whereas the levels of induction of both P4501A1 protein and CYP1A1 mRNA were reduced by >80% in the H4 cell line. Importantly, gel mobility shift analysis and Western blotting showed that the same level of AHR/ARNT complexes could be detected in cells treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin during hypoxia and normoxia. These data suggest that the effects of hypoxia on AHR-mediated gene regulation occur distal to the formation of AHR/ARNT complexes and imply that functional interference between hypoxia and AHR-mediated signaling does not occur through competition for ARNT protein.

Animals↗

PubMed1981

Acute reversible proteinuria induced by infusion of the polycation hexadimethrine.

To test the hypothesis that neutralization of polyanions of the glomerular filter in vivo will lead to loss of charge-dependent glomerular permselectivity, we have infused i.v. the polycation hexadimethrine (HDM) into rats. Heavy proteinuria resulted after a lag period of 30 to 50 min, and it resolved when the infusion was stopped. Concurrent administration of heparin prevented the proteinuria. Urinary proteins were examined by immunoelectrophoresis, isoelectric focusing with immunofixation, and sodium dodecylsulfate polyacrylamide electrophoresis. The major protein was rat albumin, but there were also large quantities of intact rat IgG. HDM was bound at known sites of glomerular polyanion in the laminae rarae of the basement membrane and on the epithelial cell glycocalyx. Associated with this binding were reversible abnormalities of the epithelial cells similar to those seen during in vitro neutralization of glomerular polyanion. Aside from proteinaceous tubular casts, no other histologic abnormality was noted. These studies provide direct evidence that neutralization of glomerular polyanions in vivo results in heavy proteinuria. The appearance of substantial quantities of rat IgG in the urine implies that abnormalities of size as well as charge-dependent permselectivity occur, suggesting that the polyanions of the glomerular filter may be important in maintaining its structure as well as its function.

Animals↗

PubMed1980

A rapid method for embedding tissues for electron microscopy using 1,4-dioxane and Polybed 812.

A rapid method for embedding tissues for electron microscopy is described. This method, which can be completed within 5 hr, uses 1,4-dioxane as the final dehydrating agent and Polybed 812 as the embedding medium. Satisfactory preservation of cellular structures is consistently achieved with a variety of normal and diseased tissues. This method may be of particular value to diagnostic electron microscopy laboratories where time and simplicity are critical.

Animals↗

PubMed1979

The role of monocytes in serum sickness nephritis.

We have investigated the pathogenesis of glomerular hypercellularity seen in acute serum sickness nephritis induced in rabbits with bovine serum albumin (BSA). The increase in cellularity began with the first stages of immune clearance of BSA, with a peak cellularity occuring at the time of onset of proteinuria. Although there was a significant increase in the fraction of glomerular cells incorporating [3H]thymidine, first seen at the onset of proteinuria, this increase occurred too late and was too small to explain the observed rate of increase in glomerular cellularity. On the other hand, a striking monocytic infiltration of the glomeruli was documented by electron microscopy and by staining for nonspecific esterase. This monocytic infiltration paralleled the observed course of glomerular hypercellularity and was quantitatively sufficient to explain the total increase seen. It appears, therefore, that glomerular hypercellularity seen in this model is principally a result of monocyte infiltration.

Animals↗