Neuroprotective Effects of BAPTA-AM: A Dose-response Study and Estimation of Therapeutic Window

ABSTRACT

In central neurons, an excessive or sustained rise in the concentration of free cytoplasmic Ca2+ ions([Ca2+]i) after hypoxia may promote rapid neurodegeneration both in vitro and in vivo. Treating cells with Ca2+ chelating agents may prevent or delay a loss of cellular Ca2+ homeostasis after hypoxic injury and thus constitute an effective strategy for minimizing neuronal damage. Cell-permeant Ca2+ chelators such as 1,2-bis-(2-aminophenoxy) ethrane -N,N,N',N' -tetraacetic acid acetoxymethyl ester(BAPTA-AM) have shown evidence of neuroprotective effect against hypoxic neuronal injury. This study was designed to examine dose response and to estimate therapeutic window of BAPTA-AM for the recovery from hypoxia in vitro. Electrophysiological studies were made in CA1 neurons in rat hippocampal slices which were superfused with artificial cerebrospinal fluid(ASCF) in tissue chamber. Hypoxia was induced by replacement of 95% N2+5% CO2 from 95% O2+5% CO2 for 20min. Recovery from hypoxic injury was evaluated by using a percentage recovery of population spike. BAPTA-AM in concentration of 1, 10 and 50micrometer were administered to the artificial cerebrospinal fluid(ASCF) for 2 hours prior to hypoxia, simultaneous with hypoxia and after hypoxia. The experimental specimens were divided to seven groups and each group was compared to control ASCF group. Recovery of population spike after hypoxia was about 70% in control ASCF group, which was mild type hypoxic injury. BAPTA-AM in 10 micrometer concentration, when given just prior to hypoxia, enhanced recovery of poppulation spikes at 15 and 30min following reoxygenation(p<0.05), in comparison with control ASCF. BAPTA-AM had no neuroprotective acitvity when given after the onset of hypoxia. Also, BAPTA-AM in 1 and 50 micrometer concentration did not accentuate recovery of population spike after hypoxia. Dose response curve was inverted U-shape and the response was maximun in 10 micrometer concentration of BAPTA-AM.