Contribution of Kir2 potassium channels to ATP-induced cell death in brain capillary endothelial cells and reconstructed HEK293 cell model

Cellular turnover of brain capillary endothelial cells (BCECs) by the balance of cell proliferation and death is essential for maintaining the homeostasis of the blood-brain barrier. Stimulation of metabotropic ATP receptors (P2Y) transiently increased intracellular Ca2+ concentration ([Ca2+]i) in t-BBEC 117, a cell line derived from bovine BCECs. The [Ca2+]i rise induced membrane hyperpolarization via the activation of apamin-sensitive small-conductance Ca2+-activated K+ channels (SK2) and enhanced cell proliferation in t-BBEC 117. Here, we found anomalous membrane hyperpolarization lasting for over 10 min in response to ATP in similar to 15% of t-BBEC 117, in which inward rectifier K+ channel (Kir2.1) was extensively expressed. Once anomalous hyperpolarization was triggered by ATP, it was removed by Ba2+ but not by apamin. Prolonged exposure to ATP gamma S increased the relative population of t-BBEC 117, in which the expression of Kir2.1 mRNAs was significantly higher and Ba2+-sensitive anomalous hyperpolarization was observed. The cultivation of t-BBEC 117 in serum-free medium also increased this population and reduced the cell number. The reduction of cell number was enhanced by the addition of ATP gamma S and the enhancement was antagonized by Ba2+. In the human embryonic kidney 293 cell model, where SK2 and Kir2.1 were heterologously coexpressed, [Ca2+]i rise by P2Y stimulation triggered anomalous hyperpolarization and cell death. In conclusion, P2Y stimulation in BCECs enhances cell proliferation by SK2 activation in the majority of cells but also triggers cell death in a certain population showing a substantial expression of Kir2.1. This dual action of P2Y stimulation may effectively facilitate BCEC turnover.