A specific 70K protein found in epileptic rat cortex: induction of bursting activity and negative resistance by its intracellular application in Euhadra neurons.
The effect of 70-kD protein (P70, a specific protein found in cobalt-induced epileptogenic focus of rat cerebral cortex) on membrane properties was examined in identified neurons of the snail, Euhadra peliomphala, using the pressure injection method combined with the voltage-clamp technique. In neurons that normally exhibited spontaneous regular firing, intracellular injection of P70 elicited bursting activity and a negative slope resistance (NSR) region in their current-voltage (I-V) curve in a manner corresponding to the duration of its injection. These responses were suppressed by prior injection of an antibody to P70 into the neurons, and were markedly inhibited by a reduction of extracellular Na+ ions and the anticonvulsant agent phenytoin, but not by Co(2+)-substituted Ca(2+)-free saline. In addition, intracellularly applied P70 potentiated both bursting activity and the NSR induced by a Na channel activator, veratridine. However, prior application of a saturating dose of this activator occluded the effect of P70. These results suggest that P70 elicits a Na(+)-dependent negative resistance, which may contribute to the generation of bursting activity.
Onozuka
M
M
Department of Anatomy, Gifu University School of Medicine, Japan.
Imai
S
S
Furuichi
H
H
Ozono
S
S
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000918:Antibody Specificity; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D004827:Epilepsy / Q000378:metabolism*; D008839:Microelectrodes; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010672:Phenytoin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012908:Snails / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology
D000888:Antibodies, Anti-Idiotypic; D009419:Nerve Tissue Proteins; D010672:Phenytoin; D014701:Veratridine; D012964:Sodium; D002118:Calcium