Delayed increase in intracellular Na+ in cerebral cortical slices during severe hypoxia as measured by double quantum filtered 23Na+ NMR.
We have used double quantum filtered (DQF) 23Na+ nuclear magnetic resonance (NMR) spectroscopy without shift reagents in order to monitor intracellular Na+ (Na+i) in a cortical brain slice preparation. The external Na+ (Na+o) signal was reduced by 95% by the DQF sequence compared with the directly observed 23Na+. The DQF 23Na+ signal is not exclusively due to Na+i, however, as 40% of this signal appears to arise from Na(+)-ions interacting with extracellular membrane proteins or proteins exposed at the cut surfaces of the slices. Veratridine increased instantly the DQF 23Na+ signal so that it reached 130.4 +/- 5.0% by 12 min. This shows that there was a significant contribution from Na+i in the DQF 23Na+ NMR spectra. Hypoxia of 30 min duration in the presence of 10 nM glucose did not influence intensity of the DQF 23Na+ signal. Aglycaemic hypoxia caused complete collapse of phosphocreatine (PCr) within 7 min whereas DQF 23Na+ first increased 15 min after the insult. This increase reached its maximal value of 125% after 25 min. There was an incomplete recovery of the DQF 23Na+ after aglycaemic hypoxia to 110% of the control value parallel to poor metabolic recovery. The presence of 10 mM extracellular Mg2+ had no apparent effect on the aglycaemic hypoxia-induced rise in Na+i indicating that it was linked to Ca2+ influx. Tetrodotoxin (TTx, 4.7 microM) did not influence the rise of Na+i caused by aglycaemic hypoxia. These results indicate that elevation of Na+i is a late consequence of energy failure in the cerebral cortex.
Brooks
K J
KJ
Department of Biochemistry and Biotechnology, A.I. Virtanen Institute, University of Kuopio, Finland.
Pirttilä
T R
TR
Kauppinen
R A
RA
D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism*; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D011789:Quantum Theory; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*
D012964:Sodium