Acta Pathologica Microbiologica Scandinavica Series A :Pathology, 2009
Asbestos fibers, silica dust and glass fibers induced aggregation of the pericellular matrix fibr... more Asbestos fibers, silica dust and glass fibers induced aggregation of the pericellular matrix fibronectin when added to the growth medium of cultured human fibroblasts as judged by immunofluorescence microscopy. Direct binding experiments and analysis of the bound proteins by (SDS‐polyacrylamide gel electrophoresis) revealed an adsorption of purified plasma fibronectin to glass fibers, amosite, crocidolite and silica but not to anthophyllite and chrysotile A and B. The results suggest that aggregation of the pericellular fibronectin by these fibrogenic materials may be involved in the initial stages of the development of fibrosis in vivo.
The effects of pH, temperature, block of energy production, calcium/calmodulin, protein phosphory... more The effects of pH, temperature, block of energy production, calcium/calmodulin, protein phosphorylation, and cytoskeleton-disrupting agents (cytochalasin D, nocodazole) on the integrity of the membrane skeleton were studied in polarized MDCK cells. The intracellular distributions of alpha-fodrin, actin, and ankyrin were monitored by immunofluorescence microscopy. The membrane skeleton, once assembled, seemed to be quite stable; the only factors releasing alpha-fodrin from the lateral walls were the acidification of the cytoplasm and the depletion of extracellular calcium ions. Upon cellular acidification, some actin was also released from its normal location along the lateral walls and was seen in colocalization with alpha-fodrin in the cytoplasm, whereas ankyrin remained associated with the lateral walls. No accumulation of plasma membrane lipids was observed in the cytoplasm of acidified cells, as visualized by TMA-DPH. These results suggest that the linkages between the fodrin-actin complex and its membrane association sites are broken upon acidification. The pH-induced change in alpha-fodrin localization was reversible upon restoring the normal pH. Reassembly of the membrane skeleton, however, required temperatures above +20 degrees C, normal energy production, proper cell-cell contacts, and polymerized actin. Release of alpha-fodrin from the lateral walls to the cytoplasm was also observed upon depletion of extracellular calcium ions. This change was accompanied by the disruption of cell-cell contacts, supporting the role of proper cell-cell contacts in the maintenance of the membrane skeleton polarity. These results suggest that local alterations of the cytoplasmic pH and calcium ion concentration may be important in regulating the integrity of the membrane skeleton.
Acta Pathologica Microbiologica Scandinavica Series A :Pathology, 2009
Asbestos fibers, silica dust and glass fibers induced aggregation of the pericellular matrix fibr... more Asbestos fibers, silica dust and glass fibers induced aggregation of the pericellular matrix fibronectin when added to the growth medium of cultured human fibroblasts as judged by immunofluorescence microscopy. Direct binding experiments and analysis of the bound proteins by (SDS‐polyacrylamide gel electrophoresis) revealed an adsorption of purified plasma fibronectin to glass fibers, amosite, crocidolite and silica but not to anthophyllite and chrysotile A and B. The results suggest that aggregation of the pericellular fibronectin by these fibrogenic materials may be involved in the initial stages of the development of fibrosis in vivo.
The effects of pH, temperature, block of energy production, calcium/calmodulin, protein phosphory... more The effects of pH, temperature, block of energy production, calcium/calmodulin, protein phosphorylation, and cytoskeleton-disrupting agents (cytochalasin D, nocodazole) on the integrity of the membrane skeleton were studied in polarized MDCK cells. The intracellular distributions of alpha-fodrin, actin, and ankyrin were monitored by immunofluorescence microscopy. The membrane skeleton, once assembled, seemed to be quite stable; the only factors releasing alpha-fodrin from the lateral walls were the acidification of the cytoplasm and the depletion of extracellular calcium ions. Upon cellular acidification, some actin was also released from its normal location along the lateral walls and was seen in colocalization with alpha-fodrin in the cytoplasm, whereas ankyrin remained associated with the lateral walls. No accumulation of plasma membrane lipids was observed in the cytoplasm of acidified cells, as visualized by TMA-DPH. These results suggest that the linkages between the fodrin-actin complex and its membrane association sites are broken upon acidification. The pH-induced change in alpha-fodrin localization was reversible upon restoring the normal pH. Reassembly of the membrane skeleton, however, required temperatures above +20 degrees C, normal energy production, proper cell-cell contacts, and polymerized actin. Release of alpha-fodrin from the lateral walls to the cytoplasm was also observed upon depletion of extracellular calcium ions. This change was accompanied by the disruption of cell-cell contacts, supporting the role of proper cell-cell contacts in the maintenance of the membrane skeleton polarity. These results suggest that local alterations of the cytoplasmic pH and calcium ion concentration may be important in regulating the integrity of the membrane skeleton.
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