Potassium ion homeostasis and mitochondrial redox activity in brain: Relative changes as indicators of hypoxia

S. J. Milito, C. N. Raffin, M. Rosenthal, Thomas Sick

Research output: Contribution to journalArticle

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Abstract

This study was directed at relating ion transport and mitochondrial redox activity during hypoxia, as a step toward definition of brain oxygen sufficiency. To accomplish this, extracellular potassium ion activity (K+o) was recorded by ion-selective microelectrodes while reduction/oxidation (redox) ratios of cytochrome oxidase (cytochrome a,a3) were monitored by reflection spectrophotometry in cerebral cortex of rats anesthetized with pentobarbital. In normoxia, neuronal activation by direct cortical stimulation produced transient oxidation of cytochrome a,a3 and elevation of K+o. Moderate hypoxia (P(a)O2 above 50 mm Hg) resulted in reduction of cytochrome a,a3 but only slight elevation of K+o. At this level of hypoxia, cytochrome a,a3 continued to respond to neuronal activation with transient shifts toward oxidation and rates of K+o reaccumulation were unchanged from control. When P(a)O2 was further decreased below a critical threshold, stimulus-provoked oxidative responses of mitochondrial reactants were replaced by shifts toward reduction, but rates of reaccumulation of K+, spilled into the extracellular space by neuronal activation, remained unchanged. Only during severe hypoxia (P(a)O2 less than 20 mm Hg) was it possible in some animals to record a slowing in the reaccumulation of K+o without provocation of spreading cortical depression. These data indicate that ion transport activity in cerebral cortex is more refractory to hypoxia than is mitochondrial redox functioning. They suggest an in vivo parallel to the 'cushioning' effect of mitochondria in vitro, in which oxygen consumption remains constant despite fluctuations in oxygenation and redox ratios, and also that there may be a greater anaerobic capacity to provide energy for ion transport in mammalian brain than has previously been appreciated.

Original languageEnglish
Pages (from-to)155-162
Number of pages8
JournalJournal of Cerebral Blood Flow and Metabolism
Volume8
Issue number2
StatePublished - Jan 1 1988

Fingerprint

Electron Transport Complex IV
Potassium
Homeostasis
Ions
Ion Transport
Brain
Cerebral Cortex
Cortical Spreading Depression
Spectrophotometry
Extracellular Space
Microelectrodes
Pentobarbital
Oxygen Consumption
Mitochondria
Hypoxia
Oxygen

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism
  • Neuroscience(all)

Cite this

Potassium ion homeostasis and mitochondrial redox activity in brain : Relative changes as indicators of hypoxia. / Milito, S. J.; Raffin, C. N.; Rosenthal, M.; Sick, Thomas.

In: Journal of Cerebral Blood Flow and Metabolism, Vol. 8, No. 2, 01.01.1988, p. 155-162.

Research output: Contribution to journalArticle

Milito, S. J. ; Raffin, C. N. ; Rosenthal, M. ; Sick, Thomas. / Potassium ion homeostasis and mitochondrial redox activity in brain : Relative changes as indicators of hypoxia. In: Journal of Cerebral Blood Flow and Metabolism. 1988 ; Vol. 8, No. 2. pp. 155-162.
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