Basement membrane changes

A decrease in basement membrane thickening in diabetics to levels close to these found in subjects without diabetes was reported by Camerini-Davalos et al. (1988), who treated 35 patients with Type-II diabetes and compared the results with those obtained with placebo. However, since plasma glucose and HbA] also decreased significantly, basement-membrane changes were felt to be a consequence of effective oral medication and not due to a specific sulphonylurea agent. 

L15. Lubec, G., Legenstein, E., Poliak, A., and Meznik, E., Glomerular basement membrane changes, Hb Aj. and urinary excretion of acid glycosaminoglycans in children with diabetes mellitus. Clin. Chim. Acta 103, 45-49 (1980). 

Jampol LM, Lahov M, Albert DM, et al. Ocular clinical findings and basement membrane changes in Goodpasture s syndrome. Am J Ophthalmol 1975 79(3) 452-463. 

Spontaneous comeal dystrophy and generalized basement membrane changes in Fischer-344 rats. Toxicol Path. 20 357 (1992). 

The vitreous is a transparent extracellular matrix occupying the space between the posterior lens and the retina and, in the majority of vertebrate species, constitutes the major f)art of the volume of the eye. Embryo-logically it can be considered as the basement membrane of the retina. It provides a mechanical support for surrounding tissues and acts as a shock absorber by virtue of its viscoelastic properties (Balzas and Delinger, 1984). Vitreous consists mainly of water (98%) and colloids (0.1%) with ions and low molecular weight solutes making up the remainder. It is not fully developed at birth, and changes in both volume and chemical composition occur postnatally. 

The transition from mesenchyme to epithelium involves biochemical changes in the cells and the extracellular matrix, N-CAM expression on cell surfaces disappears, replaced by L-CAM (uvomorulin). Vimentin, a characteristic cytoskeletal component of mesenchyme, disappears, and cytokeratin, characteristic of epithelia, appears. There is a decrease in collagen I extracellularly and an increase in the basement membrane components laminin and collagen IV. 

Charge selectivity is probably mediated mainly by the polyanionic glycosamino-glycans present in the glomerular basement membrane (C5, G6). This barrier restricts mostly the movement of relatively small polyanionic proteins (molecular weight 70-150 kDa), mainly albumin. Loss of charge selectivity is believed to be the main cause of albuminuria (selective proteinuria) in minimal change disease (B10). 

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