Na+-dependent sources of intra-axonal Ca2+ release in rat optic nerve during in vitro chemical ischemia.

Abstract

The contribution of intracellular stores to axonal Ca2+ overload during chemical ischemia in vitro was examined by confocal microscopy. Ca2+ accumulation was measured by fluo-4 dextran (low-affinity dye, KD approximately 4 microM) or by Oregon Green 488 BAPTA-1 dextran (highaffinity dye, KD approximately 450 nM). Axonal Na+ was measured using CoroNa Green. Ischemia in CSF containing 2 mM Ca2+ caused an approximately 3.5-fold increase in fluo-4 emission after 30 min, indicating a large axonal Ca2+ rise well into the micromolar range. Axonal Na+ accumulation was enhanced by veratridine and reduced, but not abolished, by TTX. Ischemia in Ca2+-free (plus BAPTA) perfusate resulted in a smaller but consistent Ca2+ increase monitored by Oregon Green 488 BAPTA-1, indicating release from intracellular sources. This release was eliminated in large part when Na+ influx was reduced by replacement with N-methyl-D-glucamine (NMDG+; even in depolarizing high K+ perfusate), Li+, or by the application of TTX and significantly increased by veratridine. Intracellular release also was reduced significantly by neomycin or 1-(6-[(17beta-methoxyestra-1,3,5 [10]-trien-17-yl) amino] hexyl)-1H-pyrrole-2,5-dione (U73122 [GenBank]) (phospholipase C inhibitors), heparin [inositol trisphosphate (IP3) receptor blocker], or 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one (CGP37157; mitochondrial Na+/Ca2+ exchange inhibitor) as well as ryanodine. Combining CGP37157 with U73122 [GenBank] or heparin decreased the response more than either agent alone and significantly improved electrophysiological recovery. Our conclusion is that intra-axonal Ca2+ release during ischemia in rat optic nerve is mainly dependent on Na+ influx. This Na+ accumulation stimulates three distinct intra-axonal sources of Ca2+: (1) the mitochondrial Na+/Ca2+ exchanger driven in the Na+ import/Ca2+ export mode, (2) positive modulation of ryanodine receptors, and (3) promotion of IP3 generation by phospholipase C.

• Authors: Maria A Nikolaeva, Ballari Mukherjee, Peter K Stys
• Journal: The Journal of neuroscience : the official journal of the Society for Neuroscience (J Neurosci) Vol. 25 Issue 43 Pg. 9960-7 (Oct 26 2005) ISSN: 1529-2401 [Electronic] United States
• PMID: 16251444 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anesthetics, Local
• Chelating Agents
• Enzyme Inhibitors
• Fluorescent Dyes
• sodium nitride
• Tetrodotoxin
• Egtazic Acid
• Veratridine
• Sodium
• Glucose
• 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
• Nitrogen
• Calcium

Topics

• Anesthetics, Local (pharmacology)
• Animals
• Axons (drug effects, metabolism)
• Calcium (metabolism, pharmacology)
• Chelating Agents (pharmacology)
• Drug Interactions
• Egtazic Acid (analogs & derivatives, pharmacology)
• Enzyme Inhibitors (pharmacology)
• Fluorescent Dyes (metabolism)
• Glucose (deficiency)
• In Vitro Techniques
• Ischemia (etiology, metabolism)
• Male
• Microscopy, Confocal (methods)
• Nitrogen (administration & dosage)
• Optic Nerve (cytology, metabolism)
• Rats
• Rats, Long-Evans
• Sodium (metabolism)
• Tetrodotoxin (pharmacology)
• Time Factors
• Veratridine (pharmacology)