The Role of ATP and P2X7 in Upregulation of Vasocontractile ET‐B Receptors in Basilar Arteries

Abstract

Cerebrovascular disease is one of the main causes of death in the developed countries. Several G‐protein coupled receptors, such as the Endothelin‐B receptor (ET‐B), are upregulated after a stroke. These receptors cause constriction in the blood vessels and reduce blood flow, causing further damage and reduced chances of recovery. Our group has previously shown that MEK/ERK1/2 inhibition greatly reduced the receptor upregulation and the cerebral damage. Extracellular ATP is a short‐range signal important in the regulation of both the blood flow and also in long term cellular modifications. One of the receptors for ATP, the P2X7 receptor, is of high interest, as it can be involved in apoptosis, proliferation, and ERK1/2 signaling. We hypothesized that ATP could be an important activator of MEK/ERK1/2 and contribute to the upregulation of contractile receptors. Ex vivo ET‐B receptor upregulation in basilar arteries (assessed by the specific agonist sarafotoxin 6c (S6c) in a myograph) can be induced by incubation of artery segments in DMEM media for 48 hours (organ culture). The changes are similar to those observed in vivo in experimental stroke. Surprisingly, adding apyrase (an ATP degrading enzyme) further increased the contraction induced by S6c and was nearly mimicked by the specific P2X7 antagonist Az10606120. The addition of a P2X7 agonist (10µM BzATP) during organ culture had little effect, indicating that the lower ATP concentrations are the important stimuli. In conclusion, ATP and P2X7 appear to be important in the upregulation of ET‐B receptors during organ culture and play a beneficial role because inhibiting them causes an increased upregulation of contractile ET‐B receptors.Funding: Lundbeck foundation (R167‐2013‐15379) and Lundbeck Grant of excellence