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Endothelial cells were isolated with high viability (greater than 93%) from porcine brain capillaries by Percoll gradient centrifugation after purely enzymatic digestion. Primary cultures were grown to confluent cell monolayers and quantitated for the activity of gamma-glutamyl transpeptidase. The gamma-glutamyl transpeptidase activity starts from a high enzymatic level, decreases with time in culture to about 15% of the initial value, and remains constant at this level after day 10 in culture. The activity progression depends on surface conditions. In the presence of collagen, an exponential decrease starts immediately after seeding, with a time constant of 70 +/- 10 h. In the absence of collagen, gamma-glutamyl transpeptidase activity first decreases on day 1 after plating, recovers to the initial value on day 2 and 3 and afterwards declines exponentially to a low and constant activity level. Ethanol added to the cell culture at a time when low constant activity is reached, reactivates the gamma-glutamyl transpeptidase to 30% of the initial value.

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