ABSTRACT
The aim of this study was to evaluate the intracellular cytosolic calcium concentration ([Ca(2+)](i)) changes induced by activation of ionotropic glutamate receptors in cultured hippocampal neurons after repeated brief episodes of hypoxia. To investigate what kinds of ionotropic glutamate receptors are involved we used specific agonists for AMPA- and NMDA-type glutamate receptors. Measurements of [Ca(2+)](i) in cultured hippocampal neurons were made by imaging Fura-2AM loaded hippocampal cells. In the rat hippocampal slice method, field potential measurements in CA1 pyramidal neurons were used. The main result of our study is that brief hypoxic episodes progressively depress the [Ca(2+)](i) increases induced by agonists of AMPA and NMDA glutamate receptors in cultured hippocampal neurons. An effectiveness of this depression is increased from the first hypoxic episode to the third one. Hypoxic preconditioning effect is observed during 10-20 min after termination of hypoxic episode and depends on [Ca(2+)](i) response amplitudes to agonists before hypoxia. In contrast to AMPA receptor activation, NMDA receptor activation before hypoxia induce the spontaneous [Ca(2+)](i) increase about 3 min after each hypoxic episode. These spontaneous [Ca(2+)](i) increases may be an indicator of the development of posthypoxic hyperexcitability in hippocampal neurons. Our results suggest that brief hypoxia-induced depression of the glutamate receptor-mediated [Ca(2+)](i) responses contributes to the development of rapid hypoxic preconditioning in hippocampal CA1 neurons.
Subject(s)
Calcium/metabolism , Cell Hypoxia/physiology , Hippocampus/cytology , Neurons/metabolism , Receptors, Ionotropic Glutamate/metabolism , Animals , Cell Hypoxia/drug effects , Excitatory Amino Acid Agonists/pharmacology , In Vitro Techniques , Intracellular Fluid/drug effects , Intracellular Fluid/metabolism , Male , N-Methylaspartate/pharmacology , Neurons/cytology , Neurons/drug effects , Rats , Rats, Wistar , Time Factors , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacologyABSTRACT
The aim of this study was to investigate the effects of apamin, a selective blocker of SK(Ca) channels, on the repeated brief hypoxia-induced posthypoxic hyperexcitability and rapid hypoxic preconditioning in hippocampal CA1 pyramidal neurons in vitro. The method of field potentials measurement in CA1 region of the rat hippocampal slices was used. Application of apamin (50nM) to the hippocampal slices during hypoxic episodes significantly abolished posthypoxic hyperexcitability induced by brief hypoxic episodes. However, in contrast to our previous results with iberiotoxin, a selective blocker of BK(Ca) channels, apamin significantly enhanced the depressive effect of brief hypoxia on the PS amplitude during hypoxic episode and did not abolish the rapid hypoxic preconditioning in CA1 pyramidal neurons. Present results indicate that SK(Ca) channels, along with previously implicated BK(Ca) channels, play an important role in the development of posthypoxic hyperexcitability induced by brief hypoxic episodes in CA1 pyramidal neurons. However, SK(Ca) channels, in contrast to the BK(Ca) channels, are not involved in the rapid hypoxic preconditioning in CA1 hippocampal region in vitro.
