Cytosolic Ca2+ changes during in vitro ischemia in rat hippocampal slices: major roles for glutamate and Na+-dependent Ca2+ release from mitochondria.
This work determined Ca2+ transport processes that contribute to the rise in cytosolic Ca2+ during in vitro ischemia (deprivation of oxygen and glucose) in the hippocampus. The CA1 striatum radiatum of rat hippocampal slices was monitored by confocal microscopy of calcium green-1. There was a 50-60% increase in fluorescence during 10 min of ischemia after a 3 min lag period. During the first 5 min of ischemia the major contribution was from Ca2+ entering via NMDA receptors; most of the fluorescence increase was blocked by MK-801. Approximately one-half of the sustained increase in fluorescence during 10 min of ischemia was caused by activation of Ca2+ release from mitochondria via the mitochondrial 2Na+-Ca2+ exchanger. Inhibition of Na+ influx across the plasmalemma using lidocaine, low extracellular Na+, or the AMPA/kainate receptor blocker CNQX reduced the fluorescence increase by 50%. The 2Na+-Ca2+ exchange blocker CGP37157 also blocked the increase, and this effect was not additive with the effects of blocking Na+ influx. When added together, CNQX and lidocaine inhibited the fluorescence increase more than CGP37157 did. Thus, during ischemia, Ca2+ entry via NMDA receptors accounts for the earliest rise in cytosolic Ca2+. Approximately 50% of the sustained rise is attributable to Na+ entry and subsequent Ca2+ release from the mitochondria via the 2Na+-Ca2+ exchanger. Sodium entry is also hypothesized to compromise clearance of cytosolic Ca2+ by routes other than mitochondrial uptake, probably by enhancing ATP depletion, accounting for the large inhibition of the Ca2+ increase by the combination of CNQX and lidocaine.
Zhang
Y
Y
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
Lipton
P
P
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D002546:Ischemic Attack, Transient / Q000378:metabolism*; D007700:Kinetics; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D016202:N-Methylaspartate / Q000494:pharmacology*; D017966:Pyramidal Cells / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013997:Time Factors
D019831:Sodium-Calcium Exchanger; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D008012:Lidocaine; D012964:Sodium; D002118:Calcium