Different phenotypes of cultured microvessel endothelial cells obtained from bovine corpus luteum. Study by light microscopy and by scanning electron microscopy (SEM).

Morphological heterogeneity has not been documented for cultured endothelial cells isolated from the microvascular bed of any organ. As the corpus luteum depends on a rich microvascularization, endothelial cells were dislodged from developing corpora lutea by mechanical dissection followed either by collagenase digestion or by no digestion. Cell separation was carried out by Percoll density centrifugation. Although the yield of intact cells was higher with collagenase treatment than without, successful endothelial cell cultures were only established when cells remained untreated. Viewed by light microscopy after an average lag phase of 10 days, five different phenotypes of endothelial cells were found under similar simple culture conditions: isomorphic epithelioid, polymorphic epithelioid, spindle-shaped, round, and phase-dense phenotypes. Monolayers appeared within 2-4 weeks. After an additional period of 2-4 weeks, tubular forms with a specific pattern were noted for types 1-3, the so-called pseudotubular forms for type 4, and none for type 5. Cell types differed in their cytochemical and immunocytochemical responses. Examined by SEM, type 1 displayed a more conspicuous surface anatomy than type 2. Types 3-5 demonstrated striking cell processes that were characteristic of each type. Tubular forms of types 1 and 2 showed cell borders and a marked increase in surface specializations, whereas tubular forms of type 3 lacked detectable cell borders in the absence of a striking surface anatomy. Pseudotubular forms of type 4 developed no particular spatial organization. Thus, for the first time, morphological evidence is provided that different endothelial cell types are obtained from diverse segments of the microvascular bed.