Acidosis decreases low Ca2+ -induced neuronal excitation by inhibiting the activity of calcium-sensing cation channels in cultured mouse hippocampal neurons

• Published in: The Journal of physiology 2003-07, Vol.550 (2), p.385-399
• Main Authors: Chu, Xiang‐Ping, Zhu, Xiao‐Man, Wei, Wen‐Li, Li, Guo‐Hua, Simon, Roger P., MacDonald, John F., Xiong, Zhi‐Gang
• Format: Article
• Language: English
• Subjects: Original
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2003.043091

The effects of extracellular pH (pH o ) on calcium-sensing non-selective cation (csNSC) channels in cultured mouse hippocampal neurons were investigated using whole-cell voltage-clamp and current-clamp recordings. Decreasing extracellular Ca 2+ concentrations ([Ca 2+ ] o ) activated slow and sustained inward currents through the csNSC channels. Decreasing pH o activated amiloride-sensitive transient proton-gated currents which decayed to baseline in several seconds. With proton-gated channels inactivated by pre-perfusion with low pH solution or blocked by amiloride, decreasing pH o to 6.5 inhibited the csNSC currents with a leftward shift of the Ca 2+ dose–inhibition curve. Increasing pH to 8.5, on the other hand, caused a rightward shift of the Ca 2+ dose–inhibition curve and potentiated the csNSC currents. Intracellular alkalinization following bath perfusion of quinine mimicked the potentiation of the csNSC currents by increasing pH o , while intracellular acidification by addition and subsequent withdrawal of NH 4 Cl mimicked the inhibition of the csNSC currents by decreasing pH o . Intracellular pH (pH i ) imaging demonstrated that decreasing pH o induced a corresponding decrease in pH i . Including 30 mM Hepes in the pipette solution eliminated the effects of quinine and NH 4 Cl on the csNSC currents, but only partially reduced the effect of lowering pH o . In current-clamp recordings, decreasing [Ca 2+ ] o induced sustained membrane depolarization and excitation of hippocampal neurons. Decreasing pH o to 6.5 inhibited the low [Ca 2+ ] o -induced csNSC channel-mediated membrane depolarization and the excitation of neurons. Our results indicate that acidosis may inhibit low [Ca 2+ ] o -induced neuronal excitation by inhibiting the activity of the csNSC channels. Both the extracellular and the intracellular sites are involved in the proton modulation of the csNSC channels.