AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 5 531-R540, Copyright © 1985 by American Physiological Society
Potassium ion homeostasis and mitochondrial redox status of turtle brain during and after ischemia
T. J. Sick, E. P. Chasnoff and M. Rosenthal
To account for the remarkable capacity of turtle brain to survive without
oxygen, microelectrode recordings of extracellular potassium activity (K+o)
were made in intact brains of normoxic pentobarbital-anesthetized turtles
during and after ischemia. Changes in redox status of brain cytochrome a,a3
were recorded simultaneously by reflection spectrophotometry. Cytochrome
a,a3 became fully reduced, and K+o rose at a slow rate for approximately 60
min during complete ischemia. When K+o reached 8-12 mM, an inflection point
was observed after which K+o rapidly increased to levels above 30 mM. Full
recovery of baseline K+o and cytochrome a,a3 redox state occurred only if
brain blood flow was restored within 60 min. These data demonstrate that
maintenance of ion homeostasis in turtle brain depends on blood flow and
continued delivery of systemic substrates and that viability is threatened
if ischemia is prolonged beyond 60 min.
