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Phenytoin, electric, ionic, and metabolic responses in cortex and spinal cord
Epilepsia
|September 1, 1977
Summary
Phenytoin, an anti-seizure drug, did not enhance potassium clearance or Na+-K+-ATPase activity in the central nervous system. It moderately depressed stimulus-evoked responses, suggesting reduced cellular activation or ion exchange.
Area of Science:
- Neuropharmacology
- Neurophysiology
Background:
- Phenytoin is a widely used anti-epileptic drug.
- Its precise mechanisms of action, particularly on neuronal excitability and ion homeostasis, are not fully elucidated.
Purpose of the Study:
- To investigate the effects of phenytoin on post-tetanic potentiation (PTP) and extracellular potassium ([K+]0) levels in the spinal cord.
- To assess phenytoin's impact on neuronal oxidative metabolism and Na+-K+-activated membrane ATPase activity.
Main Methods:
- Estimation of PTP in spinal cords.
- Measurement of extracellular potassium levels using ion-selective microelectrodes.
- Optical methods to measure NADH and cytochrome a, a3 oxidation.
- Assessment of local blood flow regulation.
Main Results:
- Phenytoin did not correlate with the control of seizure activity via PTP depression.
- Phenytoin did not accelerate post-stimulation clearing of [K+]0; it often slowed it and diminished post-stimulus undershooting.
- Stimulus-evoked oxidation responses were depressed by phenytoin.
- Phenytoin did not stimulate Na+-K+-activated membrane ATPase or reduce resting redox levels of respiratory enzymes.
- Local blood flow regulation remained unaltered.
Conclusions:
- Systemic administration of therapeutic phenytoin doses does not stimulate cortical or spinal cord Na+-K+-activated membrane ATPase.
- Phenytoin moderately depresses stimulus-evoked neuronal responses, likely due to reduced potassium outflow, indicating lesser cellular activation or ion exchange.