Dixon S Jeffrey, Yu Rongguo, Panupinthu Nattapon, Wilson John X
Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, University of Western Ontario, London, Canada.
Glia. 2004 Sep;47(4):367-76. doi: 10.1002/glia.20048.
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.
细胞外液酸化可调节大脑中的神经传递和缺血性损伤。本研究的目的是探讨嘌呤和嘧啶递质对脑星形胶质细胞酸流出的影响。使用逆转录聚合酶链反应（RT-PCR），我们在大鼠原代星形胶质细胞培养物中检测到以下核苷酸受体的转录本：P2X1、P2X2、P2X3、P2X4、P2X6、P2X7、P2Y1、P2Y2、P2Y4和P2Y6。通过微生理测定法监测发现，5'-三磷酸腺苷（ATP）能迅速诱导酸流出呈双相增加，包括初始瞬态和持续平台期。与ATP相比，P2Y激动剂5'-三磷酸尿苷（UTP）诱导的初始反应小得多，但平台期相同。水解性差的ATP类似物ATPγS引起的初始反应与ATP相同，但平台期小得多，这表明后一阶段是由于核苷酸的细胞外降解所致。P2受体拮抗剂苏拉明可阻断ATP对酸流出的刺激。去除细胞外葡萄糖或升高细胞外钾离子可降低酸流出的基础速率，但不影响ATP诱导的刺激。卡里波罗德抑制钠/氢交换可抑制ATP刺激的酸流出的初始阶段。细胞内钙离子螯合剂双氨基苯氧基乙烷-四乙酸（BAPTA）降低基础酸流出并消除对ATP反应的初始阶段。总之，ATP通过星形胶质细胞上的P2核苷酸受体发挥作用，刺激质子的钙离子依赖性流出，部分是由钠/氢交换的激活介导的。细胞外液由此产生的酸化可能作为大脑中的一种细胞间信号。
