The mechanism of intracellular ATP depletion-induced Ca2+ increase in rat cerebellar granule cells

• Main Authors: Chang, Tzu-ching, 張孜菁
• Other Authors: Mei-lin Wu
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/47006012830317290668

碩士 === 國立臺灣大學 === 生理學研究所 === 85 === Chemical ischemia is a method which may deplete intracellular ATP (ATPi) and m imic the situation of low levels of ATPi during hypoxia/ischemia. This method can be achieved by inhibition of both glycolysis [using glucose-free, iodoacet ate (IAA) or 2-deoxyglucose (DOG)] and oxidative phosphorylation (u sing cyanide or rotenone). It has been observed that in neurons a low levels o f ATPi may induce a rise in intracellular Ca2+ levels and suggested that is on eof the ma in causes to induce cytotoxicity and neuronal cell death. The under lying cellular mechanism for this phenomenon is not clear. In the present stud y,we used primary cultures of neonatal rat cerebellar granule cells and found thatafter blocking both glycolysis and respiratory chain to deplete ATPi, a si gnificant Ca2+ increase was seen. We further found that a disruption of mitoch ondrialCa2+ regulation and an extracellular Ca2+ influx are the main source f or this Ca2+ increase. The pathway for Ca2+ influx is not via (i). indent Ca2+ channels,(ii). receptor-operated Ca2+ channels or (iii). NMDA or non-NMDA rec eptors/channels.It is however, can be largely blocked by Ni2+ and a phospholyp ase A2 inhibitor,mepacrine. It is also interesting to find that a product from membrane phospholipid decomposition, lysophosphatidylcholine, has similar eff ect on extracellular Ca2+influx which can be also blocked by Ni2+. Another pro duct from phospholipid decomposition, arachidonic acid (AA), may both induce a Ca2+ store release and aninflux of extracellular Ca2+. However, the effect of AA on [Ca2+]i can only be blocked partially by Ni2+.In the presence of CN- and glucose-free condition, there was no further Ca2+ increase induced either by addition of lysophosphatidylcholine or AA. These resultssuggested th at ATPi depletion may induce a release of intracellular Ca2+ and mayresult in an activation of PLA2 followed by a marked Ca2+ influx, possibly resulting fro m the membrane phospholipid decomposition. Moreover, the neuronal cell death i s probably not exclusively related to the levels of intracellular Ca2+,since i n the absence of extracellular Ca2+, incubation of metabolic inhibitors for ~ 6 hrs may still significantly induce a late cell death.