Modification of the Na+,K+-pump of glial cells within cobalt-induced epileptogenic cortex of rat.
The characteristics of a glial Na+,K+-pump dependent on extracellular K+ within epileptogenic cortex were studied electrophysiologically, biochemically and histochemically in vitro using slices from cobalt-induced epileptogenic cortex of rat. When the extracellular K+ concentration ([K+]o) was varied between 4 and 40 mM, the mean slope of membrane potential plotted against [K+]o was about 57 mV in glia from the normal cortex (tissue A) and about 44 mV in glia from the epileptogenic cortex (tissue B); whereas no significant difference in the resting membrane potential of these tissues was observed. In glia from tissue B, a marked transient hyperpolarization above control level was caused by replacement of elevated [K+]o with the normal medium. Ouabain abolished these phenomena observed in glia from tissue B, but had no effect on the membrane potential during normal [K+]o. Reduction of extracellular Na+, Ca2+ and Cl- did not significantly affect the membrane potential of glia from either tissue. In tissue A, the cells marked by intracellular injection of horseradish peroxidase after intracellular recording were protoplasmic astrocytes; in tissue B, fibrous astrocytes with abnormal processes predominated. K+-dependent stimulation of Na+,K+-ATPase activity of the astrocyte-enriched fraction and its membrane preparation from tissue B was much larger than that from tissue A. A certain amount of the reaction product of K+-pNPPase activity was seen on glial plasma membrane within tissue B but not on that from tissue A. The above findings suggest that a glial Na+,K+-pump within actively firing epileptogenic cortex may be modified to increase in its activity.
Onozuka
M
M
Department of Anatomy, Gifu University School of Medicine, Japan.
Kishii
K
K
Imai
S
S
Ozono
S
S
D000818:Animals; D001253:Astrocytes / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure; D002540:Cerebral Cortex / Q000166:cytology / Q000201:enzymology* / Q000503:physiopathology; D003035:Cobalt; D004827:Epilepsy / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology; D006651:Histocytochemistry; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis / Q000502:physiology*
D003035:Cobalt; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium