Relationship between intracellular pH and high energy phosphates in rat brain slices.

本实验观察了人工脑脊液(ACSF)二氧化碳分压升高所致的酸中毒对正常大鼠和酸预适应大鼠脑能量代谢的影响。在25℃时，用~(31)P核磁共振测量完整脑片和酸预处理脑片中高能磷酸盐和PHI的水平。当ACSF鼓泡气体中CO_2含量从5%增加到40%时，完整脑片的pH_i从7.25±0.02(Mean±SD，n=14)降至6.55±0.02(n=6)。磷酸肌酸(PCr)水平在pH_i维持在7.4~6.9之间，但在pH_i<6.8时迅速下降。PH_i从7.25降至6.55后，PCR值下降了51±0.04%(n=23)。在酸性预处理脑片中，PCR值的下降和pH_i的下降与完整脑片相似，但在pH_i介于6.6~6.4时，酸性预处理脑片的PCR值下降幅度明显小于完整脑片(71±0.04%，n=11)。这些结果表明，对酸中毒的大脑进行预处理，可以诱导大脑对随后的酸中毒时期的能量代谢产生耐受。

We examined the effect of acidosis induced by increase of CO_2 tension in artificial cerebrospinal fluid(ACSF) on energy metabolism in both of intact and acidic pre-conditioned rat brain ex vivo. The levels of high-energy phosphates and pHi in the intact and acidic preconditioned brain slices were measured using ^<31>P NMR at 25℃. When CO_2 content in bubbling gas of ACSF was increased from 5% to 40%, pH_i decreased from 7.25±0.02(mean±SD,n=14) to 6.55±0.02(n=6) in intact brain slices. The level of phosphocreatine(PCr) was maintained at pH_i between 7.4 and 6.9, but decreased rapidly at pH_i less than 6.8. Following decrease in pH_i from 7.25 to 6.55, PCr levels decreased 51±0.04%(n=23).In acidic preconditioned brain slices, the decrease of PCr level followed by decrease in pH_i was similar as that in intact slices, but at pH_i between 6.6 and 6.4 decrease of PCr level in acidic preconditioned slices was distinctly smaller than that in intact slices(71±0.04 %,n=11). These results indicate that the pretreatment of the brain with acidosis induces a tolerance in energy metabolism of the brain to subsequent periods of acidosis.