Activation of P2 nucleotide receptors stimulates acid efflux from astrocytes

Abstract

Acidification of the extracellular fluid modulates neurotransmission and ischemic injury in brain. The purpose of the present study was to investigate the effects of purine and pyrimidine transmitters on acid efflux from brain astrocytes. Using RT-PCR, we detected transcripts for the following nucleotide receptors in rat primary astrocyte cultures: P2X1, P2X2, P2X3, P2X4, P2X6, P2X7, P2Y1, P2Y2, P2Y4, and P2Y6. Adenosine 5'-triphosphate (ATP) was found to rapidly induce a biphasic increase in acid efflux, monitored by microphysiometry, consisting of an initial transient and a sustained plateau. Compared with ATP, the P2Y agonist uridine 5'-triphosphate (UTP) induced a much smaller initial response but an equal plateau. The poorly hydrolyzable ATP analogue ATPgammaS caused the same initial response as did ATP, but a much smaller plateau, suggesting that the latter phase was due to extracellular degradation of nucleotides. The P2 receptor antagonist, suramin, blocked stimulation of acid efflux by ATP. Removal of extracellular glucose or elevation of extracellular K+ decreased the basal rate of acid efflux but not the stimulation induced by ATP. Inhibition of Na+/H+ exchange by cariporide suppressed the initial phase of ATP-stimulated acid efflux. The intracellular Ca2+ chelator bisaminophenoxyethane- tetraacetic acid (BAPTA) lowered basal acid efflux and abolished the initial phase of the response to ATP. In conclusion, ATP acts through P2 nucleotide receptors on astrocytes to stimulate the Ca2+ -dependent efflux of protons, mediated in part by activation of Na+/H+ exchange. The resulting acidification of the extracellular fluid may serve as an intercellular signal in brain.

In vitro and in vivo evidence for a role of the P2X7 receptor in the release of IL-1β in the murine brain

“…As shown by our in vitro results, LPS-induced IL-6 production is probably mediated by an effect of ATP on other purinergic receptors than P2X 7 R. Both microglia and astrocytes are important sources of IL-6 (Lee et al, 1993;van Wagoner and Benveniste, 1999). As both microglia and astrocytes express TLR4 (Bowman et al, 2003;Chakravarty and Herkenham, 2005) and P2Y receptors (Dixon et al, 2004;Franke et al, 2004;Fumagalli et al, 2003;Yamakuni et al, 2002) it is therefore possible that LPS as well as other inflammatory cytokines directly trigger IL-6 release by these cells independently of IL-1β.…”

P2Y 1 receptor signaling is controlled by interaction with the PDZ scaffold NHERF-2

“…Second, the ability of NHERF proteins to interact with PKC (25) might facilitate the tethering of PKC in the vicinity of P2Y 1 R and thereby modulate the ability of PKC to phosphorylate and regulate the activity of P2Y 1 R (17). Third, NHERF-2 is known to regulate the activity of Na ϩ ͞H ϩ exchangers (37) and therefore may play a role in linking P2Y 1 R to modulation of Na ϩ ͞H ϩ exchange (38). Finally, it is interesting to note that NHERF-2 has been shown to form a high-affinity complex with the cystic fibrosis transmembrane regulator (CFTR) in A6 cells (39).…”

Nucleotides affect neurogenesis and dopaminergic differentiation of mouse fetal midbrain-derived neural precursor cells

“…In addition several studies report the presence of mRNA encoding P2 receptors in astrocytes cultured from rodent brain. While the extent of analysis varies between studies, mRNAs for all subtypes of P2Y and P2X receptors have been reported [37,38]. The presence of mRNA does not prove the presence of functional protein.…”