Phenotypic changes in morphology and collagen polymorphism of cultured bovine and porcine aortic endothelium.

Endothelial cells derived from the pig aorta grow in culture with typical cobblestone morphology; after about 7 days they elongate to a more fibroblastic appearance followed by the appearance of sprouts. The sprouts can be removed by 24 h treatment with either 8-bromo-cyclic AMP or cholera toxin, when the cells revert to their original cobblestone morphology. Examination of phenotypic markers as exemplified by the collagen types synthesised in the cell layer and those released into the medium, indicated the presence of types I, III and V in the cobblestone phase; the result of sprouting and desprouting was to alter the various proportions of I, III and V in both cells and medium with the exception that type V disappeared from the medium of sprouting porcine cells. When bovine endothelial aortic cells were similarly examined, I, III and V type collagens were found in the cell layer and medium, but in vastly different proportions from those found in the pig. Sprouting and desprouting bovine endothelium produced profound changes--in the cell layer, only type V could be demonstrated, whereas I, III and V were demonstrable in the medium, albeit in differing proportions. The conclusions are firstly, that phenotypic morphological changes may or may not be accompanied by phenotypic changes in the synthesis of the various collagen markers; secondly, that the secreted collagens do not always reflect those collagens retained by the cell layer which shows sequestration of one of the collagen types; finally there is a very distinct species difference and it is not possible to extrapolate from one species to another. The ultrastructural observation that the sprouts in cultured bovine endothelium resemble everted capillaries adds value to the culture as a model system.