Nuclear membranous whorls

Summary Membranous whorls have been seen in the nuclei of peritoneal and testicular cells which had been subjected to various experimental manoeuvres. It seems likely that this is an early manifestation of cell degeneration which is demonstrated readily only by glutaraldehyde fixation, and to that extent can be regarded as a glutaraldehyde artifact. Acknowledgements. This work was supported by grants from the Medical Research Council, and the University of Sheffield Tuberculosis Research Fund, and by a grant to the Department from Unilever Ltd.I am grateful to Professor R. Barer for his advice and criticism, to Dr. G. A. Meek for guidance on electron microscopy, to Dr. E. J. Clegg for permission to use material from joint experiments. Technical and photographic assistance was provided by Messrs. P. GarLick and L. Murgatroyd and by Miss M. Tune.     

Growth-associated modifications of low-molecular-weight thiols and protein sulfhydryls in human bronchial fibroblasts

The thiol redox status of cultured human bronchial fibroblasts has been characterized at various growth conditions using thiol-reactive monobromobimane, with or without the combination of dithiotreitol, a strong reducing agent. This procedure has enabled measurement of the cellular content of reduced glutathione (GSH), total glutathione equivalents, cysteine, total cysteine equivalents, protein sulfhydryls, protein disulfides, and mixed disulfides. Passage of cells with trypsin perturbs the cellular thiol homeostasis and causes a 50% decrease in the GSH content, whereas the total cysteine content is subsequently increased severalfold during cell attachment. During subsequent culture, transient severalfold increased levels of GSH, protein-bound thiols, and protein disulfides are reached, whereas the total cysteine content gradually declines. These changes in the redox balance of both low-molecular-weight thiols and protein-bound thiols correlate with cell proliferation and mostly precede the major growth phase. When the onset of proliferation is inhibited by maintenance of cells in medium containing decreased amounts of serum, the GSH content remains significantly increased. Subsequent stimulation of growth by addition of serum results in decreased GSH levels at the onset of proliferation. In thiol-depleted medium, proliferation is also inhibited, whereas GSH levels are increased to a lesser extent than in complete medium. Exposure to buthionine sulfoximine inhibits growth, prevents GSH synthesis, and results in accumulation of total cysteine, protein-bound cysteine, and protein disulfides. For extracellular cystine, variable rates of cellular uptake correlate with the initial increase in the total cysteine content observed following subculture and with the GSH peak that precedes active proliferation. The results strongly suggest that specific fluctuations in the cellular redox balance of both free low-molecular-weight thiols and protein sulfhydryls are involved in growth regulation of normal human fibroblasts.