Potentiation of intracellular Ca²⁺ mobilization by hypoxia‐induced NO generation in rat brain striatal slices and human astrocytoma U‐373 MG cells and its involvement in tissue damage

Abstract

The relationship between nitric oxide (NO) and intracellular Ca2+ in hypoxic-ischemic brain damage is not known in detail. Here we used rat striatal slices perfused under low-oxygen and Ca2+-free conditions and cultured human astrocytoma cells incubated under similar conditions as models to study the dynamics of intracellular NO and Ca2+ in hypoxia-induced tissue damage. Exposure of rat striatal slices for 70 min to low oxygen tension elicited a delayed and sustained increase in the release of 45Ca2+. This was potentiated by the NO donors sodium nitroprusside (SNP) and spermine-NO and inhibited by N-omega-nitro-L-arginine methyl ester (L-NAME) or by the NO scavenger 2-phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl-3-oxide (PTIO). A membrane-permeant form of heparin in combination with either ruthenium red (RR) or ryanodine (RY) also inhibited 45Ca2+ release. In human astrocytoma U-373 MG cells, hypoxia increased intracellular Ca2+ concentration ([Ca2+]i) by 67.2 +/- 13.1% compared to normoxic controls and this effect was inhibited by L-NAME, PTIO or heparin plus RR. In striatal tissue, hypoxia increased NO production and LDH release and both effects were antagonized by L-NAME. Although heparin plus RR or RY antagonized hypoxia-induced increase in LDH release they failed to counteract increased NO production. These data therefore indicate that NO contributes to hypoxic damage through increased intracellular Ca2+ mobilization from endoplasmic reticulum and suggest that the NO-Ca2+ signalling might be a potential therapeutic target in hypoxia-induced neuronal degeneration.

The Effects of Hypoxia/Reoxygenation on the Physiological Behaviour of U373-Mg Astrocytes

“…After hypoxia, we observed a significant increase of [Ca 2? ] i and NO, in accordance with our previous results on astrocytes and brain striatal slices [30]. The brain has a high requirement for iron and oligodendrocytes require iron for the synthesis of myelin.…”

Endoplasmic Reticulum Dysfunction and Ca2+ Deregulation in Isolated CA1 Neurons during Oxygen and Glucose Deprivation

“…Disturbances in the Ca 2+ homeostasis within the ER may contribute to ischemic cell damage (8,(34)(35)(36)(37)(38). The ER exhibits a high Ca 2+ activity in contrast to the cytoplasm and mitochondria.…”

The Effect of Mild and Severe Hypoxia on Rat Cortical Synaptosomes

“…In fact, reperfusion after short periods of cerebral ischemia is accompanied by hyperoxidation of the mitochondrial respiratory chain (10), which is mediated by accumulation of intracellular calcium and reactive oxygen species. Moreover, tissue injury occurring after ischemia/ reperfusion is the main cause of disorders in many organs; it is multifactorial and involves hypoxia, hyperoxia, free radical damage and inflammatory responses (26,27).…”