Darby Mark, Kuzmiski J Brent, Panenka William, Feighan Denise, MacVicar Brian A
Neuroscience Research Group, Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
J Neurophysiol. 2003 Apr;89(4):1870-7. doi: 10.1152/jn.00510.2002.
ATP release from astrocytes contributes to calcium ([Ca(2+)]) wave propagation and may modulate neuronal excitability. In epithelial cells and hepatocytes, cell swelling causes ATP release, which leads to the activation of a volume-sensitive Cl(-) current (I(Cl,swell)) through an autocrine pathway involving purinergic receptors. Astrocyte swelling is counterbalanced by a regulatory volume decrease, involving efflux of metabolites and activation of I(Cl,swell) and K(+) currents. We used whole cell patch-clamp recordings in cultured astrocytes to investigate the autocrine role of ATP in the activation of I(Cl,swell) by hypo-osmotic solution (HOS). Apyrase, an ATP/ADP nucleotidase, inhibited HOS-activated I(Cl,swell), whereas ATP and the P2Y agonists, ADPbetaS and ADP, induced Cl(-) currents similar to I(Cl,swell). Neither the P2U agonist, UTP nor the P2X agonist, alpha,beta-methylene ATP, were effective. BzATP was less effective than ATP, suggesting that P2X7 receptors were not involved. P2 purinergic antagonists, suramin, RB2, and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) reversibly inhibited activation of I(Cl,swell), suggesting that ATP-activated P2Y1 receptors. Thus ATP release mediates I(Cl,swell) in astrocytes through the activation of P2Y1-like receptors. The multidrug resistance protein (MRP) transport inhibitors probenicid, indomethacin, and MK-571 all potently inhibited I(Cl.swell). ATP release from astrocytes in HOS was observed directly using luciferin-luciferase and MK-571 reversibly depressed this HOS-induced ATP efflux. We conclude that ATP release via MRP and subsequent autocrine activation of purinergic receptors contributes to the activation of I(Cl,swell) in astrocytes by HOS-induced swelling.
星形胶质细胞释放的三磷酸腺苷（ATP）有助于钙（[Ca(2+)]）波的传播，并可能调节神经元的兴奋性。在上皮细胞和肝细胞中，细胞肿胀会导致ATP释放，通过涉及嘌呤能受体的自分泌途径，这会导致激活一种容积敏感性氯离子电流（I(Cl,swell)）。星形胶质细胞的肿胀通过调节性容积减小来平衡，这涉及代谢产物的外流以及I(Cl,swell)和钾离子电流的激活。我们在培养的星形胶质细胞中使用全细胞膜片钳记录来研究ATP在低渗溶液（HOS）激活I(Cl,swell)中的自分泌作用。Apyrase，一种ATP/ADP核苷酸酶，抑制HOS激活的I(Cl,swell)，而ATP以及P2Y激动剂ADPβS和ADP诱导出类似于I(Cl,swell)的氯离子电流。P2U激动剂UTP和P2X激动剂α,β-亚甲基ATP均无效。BzATP的效果不如ATP，表明P2X7受体未参与其中。P2嘌呤能拮抗剂苏拉明、RB2和磷酸吡哆醛-6-偶氮苯-2',4'-二磺酸（PPADS）可逆地抑制I(Cl,swell)的激活，表明ATP激活了P2Y1受体。因此，ATP释放通过激活P2Y1样受体介导星形胶质细胞中的I(Cl,swell)。多药耐药蛋白（MRP）转运抑制剂丙磺舒、吲哚美辛和MK-571均强烈抑制I(Cl.swell)。使用荧光素-荧光素酶直接观察到HOS中星形胶质细胞释放的ATP，并且MK-571可逆地抑制这种HOS诱导的ATP外流。我们得出结论，通过MRP释放的ATP以及随后嘌呤能受体的自分泌激活有助于HOS诱导的肿胀激活星形胶质细胞中的I(Cl,swell)。
