Na⁺/H⁺ exchange subtype 1 inhibition during extracellular acidification and hypoxia in glioma cells

Lactacidosis is a common feature of ischaemic brain tissue, but its role in ischaemic neuropathology is still not fully understood. Na⁺/H⁺ exchange, a mechanism involved in the regulation of intracellular pH (pH_i), is activated by low pH_i. The role of Na⁺/H⁺ exchange subtype 1 was investigated during extracellular acidification and subsequent pH recovery in the absence and presence of (4-isopropyl-3-methylsulphonyl-benzoyl)-guanidine methanesulfonate (HOE642, Cariporid), a new selective and powerful inhibitor of the Na⁺/H⁺ exchanger subtype 1 (NHE-1). It was compared for normoxia and hypoxia in two glioma cell lines (C6 and F98). pH_i was monitored by fluorescence spectroscopy using the intracellularly trapped pH- sensitive dye 2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Alterations in glial cell metabolism were characterized using high-resolution ¹H, ¹³C and ³¹P NMR spectroscopy of perchloric acid extracts. NHE-1 contributed to glial pH regulation, especially at pathologically low pH_i values. NHE-1 inhibition with HOE642 during acidification caused exacerbated metabolic disorders which were prolonged during extracellular pH recovery. However, NHE-1 inhibition during hypoxia protected the energy state of glial cells.