Adenine incorporation in human and rat endothelium

Adenine (ADE) reutilisation is an important pathway of adenylate pool regen eration. Data on the rate of this process in different types of cells, its regulation and the importance of species differences is limited. In this st udy we evaluated adenine incorporation rate and the effect of metabolic fac tors on this process in human and rat endothelium and compared it to adenin e phosphoribosyltransferase (APRT) activity. Microvascular endothelial cell s from human (HE) and rat (RE) hearts and a transformed human microvascular endothelial cell line (HMEC-1) were investigated. The rate of adenine inco rporation into the adenine nucleotide pool under control conditions was 3.1 +/- 0.3, 82.8 +/- 11.1 and 115.1 +/- 11.2 pmol/min per mg protein for HE, RE and HMEC-1, respectively. In the presence of 2.5 mM ribose or elevated i norganic phosphate concentration in the medium (4.8 mM), few changes were o bserved in all types of cells. In the presence of both ribose and high inor ganic phosphate, the rate of adenine incorporation for RE and HMEC-1 was no t significantly different from control, while in HE the rate of adenine inc orporation into adenine nucleotides was increased by 75%. Activities of APR T in RE and HMEC-1 were 237.7+/-23.2 and 262.0+/-30.6 pmol/min per mg prote in respectively while the activity in HE was markedly lower 48.7+/-3.0 pmol /min per mg protein. In conclusion, nucleotide synthesis from adenine seems to be a slow process in human cardiac microvascular endothelium but it is fast and efficient in rat heart microvascular endothelial cells. Low APRT a ctivity in normal human endothelial cells seems to be the most likely mecha nism for this. However, adenine incorporation rate and APRT activity could be greatly enhanced in human endothelium, as demonstrated in transformed ce lls. (C) 1999 Elsevier Science B.V. All rights reserved.