Wilkie Michael P, Pamenter Matthew E, Alkabie Samir, Carapic Dejana, Shin Damian S H, Buck Leslie T
Department of Biology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario, Canada N2L 3C5.
Comp Biochem Physiol C Toxicol Pharmacol. 2008 Nov;148(4):355-62. doi: 10.1016/j.cbpc.2008.06.004. Epub 2008 Jun 19.
The common goldfish (Carassius auratus) is extremely anoxia tolerant and here we provide evidence that "channel arrest" in the brain of these fish contributes to ATP conservation during periods of anoxia. Whole-cell patch-clamp recordings of slices taken from the telencephalon indicated that the N-methyl-d-aspartate (NMDA) receptor, an ionotropic glutamate receptor and Ca(2+)-channel, underwent a 40-50% reduction in activity during 40 min of acute anoxia. This is the first direct evidence of channel arrest in an anoxia-tolerant fish. Because goldfish produce ethanol as a byproduct of anaerobic metabolism we then conducted experiments to determine if the observed reduction in NMDA receptor current amplitude was due to inhibition by ethanol. NMDA receptor currents were not inhibited by ethanol (10 mmol L(-1)), suggesting that channel arrest of the receptor involved other mechanisms. Longer-term (48 h) in vivo exposure of goldfish to anoxic conditions (less than 1% dissolved O(2)) provided indirect evidence that a reduction in Na(+)/K(+)-ATPase activity also contributed to ATP conservation in the brain but not the gills. Anoxia under these conditions was characterized by a decrease in brain Na(+)/K(+)-ATPase activity of 30-40% by 24 h. Despite 90% reductions in the rates of ventilation, no change was observed in gill Na(+)/K(+)-ATPase activity during the 48-h anoxia exposure, suggesting that branchial ion permeability was unaffected. We conclude that rapid "channel arrest" of NMDA receptors likely prevents excitotoxicity in the brain of the goldfish, and that a more slowly developing decrease in Na(+)/K(+)-ATPase activity also contributes to the profound metabolic depression seen in these animals during oxygen starvation.
普通金鱼（Carassius auratus）具有极强的耐缺氧能力，在此我们提供证据表明，这些鱼大脑中的“通道阻滞”有助于在缺氧期间保存ATP。对取自端脑的切片进行的全细胞膜片钳记录表明，N-甲基-D-天冬氨酸（NMDA）受体，一种离子型谷氨酸受体和钙通道，在急性缺氧40分钟期间活性降低了40-50%。这是耐缺氧鱼类中通道阻滞的首个直接证据。由于金鱼会产生乙醇作为无氧代谢的副产物，我们随后进行了实验，以确定观察到的NMDA受体电流幅度降低是否是由于乙醇的抑制作用。NMDA受体电流不受乙醇（10 mmol L(-1)）的抑制，这表明该受体的通道阻滞涉及其他机制。金鱼在体内长期（48小时）暴露于缺氧条件（溶解氧低于1%）提供了间接证据，表明Na(+)/K(+)-ATP酶活性的降低也有助于大脑而非鳃中的ATP保存。在这些条件下的缺氧表现为，到24小时时大脑中Na(+)/K(+)-ATP酶活性降低30-40%。尽管通气率降低了90%，但在48小时的缺氧暴露期间，鳃中Na(+)/K(+)-ATP酶活性未观察到变化，这表明鳃的离子通透性未受影响。我们得出结论，NMDA受体的快速“通道阻滞”可能会防止金鱼大脑中的兴奋性毒性，并且Na(+)/K(+)-ATP酶活性更缓慢的降低也有助于这些动物在缺氧期间出现的深度代谢抑制。
