ATP release from vascular endothelia occurs across Cx43 hemichannels and is attenuated during hypoxia.
BACKGROUND
Extracellular ATP is an important signaling molecule for vascular adaptation to limited oxygen availability (hypoxia). Here, we pursued the contribution of vascular endothelia to extracellular ATP release under hypoxic conditions.


RESULTS
We gained first insight from studying ATP release from endothelia (HMEC-1) pre-exposed to hypoxia. Surprisingly, we found that ATP release was significantly attenuated following hypoxia exposure (2% oxygen, 22+/-3% after 48 h). In contrast, intracellular ATP was unchanged. Similarly, lactate-dehydrogenase release into the supernatants was similar between normoxic or hypoxic endothelia, suggesting that differences in lytic ATP release between normoxia or hypoxia are minimal. Next, we used pharmacological strategies to study potential mechanisms for endothelial-dependent ATP release (eg, verapamil, dipyridamole, 18-alpha-glycyrrhetinic acid, anandamide, connexin-mimetic peptides). These studies revealed that endothelial ATP release occurs--at least in part--through connexin 43 (Cx43) hemichannels. A real-time RT-PCR screen of endothelial connexin expression showed selective repression of Cx43 transcript and additional studies confirmed time-dependent Cx43 mRNA, total and surface protein repression during hypoxia. In addition, hypoxia resulted in Cx43-serine368 phosphorylation, which is known to switch Cx43 hemi-channels from an open to a closed state.


CONCLUSIONS
Taken together, these studies implicate endothelial Cx43 in hypoxia-associated repression of endothelial ATP release.
Faigle
Marion
M
Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Tübingen, Germany.
Seessle
Jessica
J
Zug
Stephanie
S
El Kasmi
Karim C
KC
Eltzschig
Holger K
HK
D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D018031:Connexin 43 / Q000737:chemistry / Q000502:physiology*; D017931:DNA Primers / Q000737:chemistry; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D000860:Hypoxia; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic
D018031:Connexin 43; D017931:DNA Primers; D010455:Peptides; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D010100:Oxygen