AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 1 205-R210, Copyright © 1990 by American Physiological Society
Extracellular pH and suppression of electrical activity during anoxia in turtle and rat brain
Z. C. Feng, T. J. Sick and M. Rosenthal
Department of Neurology, University of Miami School of Medicine, Florida 33101.
To evaluate the contribution of extracellular H+ activity toward depression
of brain electrical activity during anoxia, extracellular pH (pHe) and
field potentials were measured in turtle and rat olfactory bulbs with
ion-selective microelectrodes. This study tests the hypothesis that unique
regulation of pHe contributes to the remarkable tolerance of turtle brain
to prolonged anoxia. Hypercapnea (20% CO2 ventilation) depressed olfactory
bulb evoked potentials 25-30% in both rat and turtle. During anoxia, evoked
potentials were completely abolished within 1 min in rat olfactory bulb but
decreased to only 40% of control after 4 h in the turtle despite similar
changes in brain pHe. Anoxia-induced acidification of turtle brain was
exacerbated by hypercapnea and was attenuated by hypocapnea or by
hypocapnea plus intravenous infusion of sodium bicarbonate. However, these
manipulations of pHe during anoxia in turtle brain had little effect on
depression of evoked potentials. We conclude that energy failure, rather
than extracellular acidification, is the major contributor toward
suppression of electrical activity in mammalian brain and that preservation
of energy balance, rather than unique pH regulation, is responsible for
protection of turtle brain during anoxia.
