Kass I S, Lipton P
J Physiol. 1986 Sep;378:313-34. doi: 10.1113/jphysiol.1986.sp016221.
The mechanism of long-term anoxic damage in brain tissue is investigated using the rat hippocampal slice as a model system. The effects of short durations of anoxia on subsequent transmission through two neural pathways are studied. 10 min of anoxia irreversibly abolishes transmission between the perforant path and the dentate granule cells while only 7 min of anoxia irreversibly abolishes transmission between the Schaeffer collaterals and the CA1 pyramidal cells. We examine the involvement of Ca2+ in this irreversible transmission damage and, also, the differential sensitivities of the dentate gyrus and CA1 regions. Substitution of a buffer containing 0 Ca2+ and 10 mM-Mg2+ during the anoxic period substantially improves the recovery of synaptic transmission in both regions of the slice. Dentate gyrus transmission recovers completely after 20 min of anoxia and CA1 transmission survives 10 min of anoxia. These results suggest that Ca2+ influx during anoxia may be an important cause of the long-term damage. The uptake of 45Ca2+ into the intracellular space of the slice is increased during anoxia. This effect is approximately twice as large in CA1 as in the dentate gyrus. Thus, in the dentate gyrus the calculated exchangeable pool of Ca2+ is increased 30% by anoxia and in the CA1 it is increased by 70%. Two incubating conditions which decrease the amount of 45Ca2+ uptake during anoxia protect transmission against long-term damage. (a) Pre-incubation of the slices with 25 mM-creatine elevates tissue phosphocreatine and attenuates the fall in adenosine 5'-triphosphate (ATP) during anoxia. This is associated with partial protection against transmission damage and an approximate 50% attenuation of the anoxic uptake of 45Ca2+. (b) Inclusion of 2 mM-cobalt in the buffer reduces the normoxic uptake of 45Ca2+ so that the uptake during anoxia is no greater than normoxic uptake in the absence of cobalt. This is associated with a complete protection against long-term transmission damage following 10 min of anoxia in the dentate gyrus. A kinetic analysis of the 45Ca2+ uptake shows that the anoxic uptake results primarily from inhibition of the unidirectional efflux of Ca2+ from the cells; there is no calculable increase in the undirectional influx. This suggests that anoxia increases Ca2+ uptake by inhibiting one or more Ca2+-extrusion processes and not by opening depolarization-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
以大鼠海马切片作为模型系统，研究脑组织长期缺氧损伤的机制。研究了短时间缺氧对两条神经通路后续传递的影响。10分钟的缺氧会不可逆地阻断穿通通路与齿状颗粒细胞之间的传递，而仅7分钟的缺氧就会不可逆地阻断谢弗侧支与CA1锥体细胞之间的传递。我们研究了Ca2+在这种不可逆传递损伤中的作用，以及齿状回和CA1区的不同敏感性。在缺氧期间用含0 Ca2+和10 mM - Mg2+的缓冲液替代，可显著改善切片两个区域突触传递的恢复。齿状回传递在缺氧20分钟后完全恢复，CA1传递在缺氧10分钟后仍能存活。这些结果表明，缺氧期间Ca2+内流可能是长期损伤的一个重要原因。缺氧期间，切片细胞内空间对45Ca2+的摄取增加。这种效应在CA1区大约是齿状回的两倍。因此，在齿状回中，经计算，缺氧使Ca2+的可交换池增加30%，在CA1区增加70%。两种降低缺氧期间45Ca2+摄取量的孵育条件可保护传递免受长期损伤。(a) 将切片用25 mM - 肌酸预孵育可提高组织磷酸肌酸水平，并减弱缺氧期间三磷酸腺苷(ATP)的下降。这与对传递损伤的部分保护以及缺氧时45Ca2+摄取量约50%的减弱有关。(b) 在缓冲液中加入2 mM - 钴可降低正常氧水平下45Ca2+的摄取，使缺氧时的摄取量不超过无钴时正常氧水平下的摄取量。这与齿状回在缺氧10分钟后对长期传递损伤的完全保护有关。对45Ca2+摄取的动力学分析表明，缺氧时的摄取主要是由于细胞Ca2+单向外流受到抑制；单向内流没有可计算的增加。这表明缺氧通过抑制一个或多个Ca2+外流过程而非通过打开对去极化敏感的Ca2+通道来增加Ca2+摄取。(摘要截选至400字)
