(Na-K)-ATPase activity in experimental epileptogenic foci

The Na+/K+ATPase activity is increased in the hippocampus after multiple status epilepticus induced by pilocarpine in developing rats

The effects of repetitive pilocarpine-induced status epilepticus (SE) in the hippocampal Na(+)/K(+)ATPase activity were studied in developing rat. Na(+)/K(+)ATPase is a membrane-bound enzyme responsible for the active transport of sodium and potassium ions through the membrane. It is necessary to maintain neuronal excitability. The malfunction of this enzyme has been associated with neuronal hyperexcitability. The pilocarpine-induced status epilepticus in developing rats leads to neuronal hyperexcitability and brain damage. We examined the activity of the Na(+)/K(+)ATPase enzyme in hippocampus of rats submitted to 1 episode of status epilepticus on postnatal day 9 and to 3 episodes of pilocarpine-induced status epilepticus on postnatal days 7, 8 and 9. Our findings showed that one status epilepticus episode does not modify the Na(+)/K(+)ATPase activity in hippocampus of rats studied 7 or 30 days later (at P16 or P39). However, an increase in the Na(+)/K(+)ATPase activity was detected in hippocampus of rats submitted to three consecutive status epilepticus during the development studied 7 (+142%) and 30 (+400%) days following the injections. In addition, a significant reduction in the Na(+)/K(+)ATPase activity was observed in control rats at P39 compared to P16. Our data suggest that multiple pilocarpine-induced status epilepticus in developing rats induce long-lasting increase in the Na(+)/K(+)ATPase activity in the hippocampus, reflecting hyperexcitability.

Na+K+ ATPase activity in the rat hippocampus: a study in the pilocarpine model of epilepsy

Biochemical abnormalities have been implicated in possible mechanisms underlying the epileptic phenomena. Some of these alterations include changes in the activity of several enzymes present in epileptic tissues. Systemic administration of pilocarpine in rats induces electrographic and behavioral limbic seizures and status epilepticus, that is followed by a transient seizure-free period (silent period). Finally a chronic phase ensues, characterized by spontaneous and recurrent seizures (chronic period), that last for the rest of the animal's life. The present work aimed to study the activity of the enzyme Na+K+ ATPase, in rat hippocampus, during the three phases of this epilepsy model. The enzyme activity was determined at different time points from pilocarpine administration (1 and 24 h of status epilepticus, during the silent and chronic period) using a spectrophotometric assay previously described by Mishra and Delivoria-Papadopoulos [Neurochem. Res. (1988) 13, 765-770]. The results showed decreased enzyme activities during the acute and silent periods and increased Na+K+ ATPase activity during the chronic phase. These data show that changes in Na+K+ ATPase activity could be involved in the appearance of spontaneous and recurrent seizures following brain damage induced by pilocarpine injection.

Phosphorylation of brain (Na+,K+)-ATPase alpha catalytic subunits in normal and epileptic cerebral cortex: I. The audiogenic mice and the cat with a freeze lesion

Partially purified (Na+,K+)-ATPase (E.C. 3.6.1.3.) was investigated in the epileptic cortex of audiogenic DBA/2 mice and in the primary and secondary foci of cats with acute or chronic freeze lesions. No differences in specific activities measured at 3 mM K+ were observed between epileptic and control cortex, except an increase of enzymic activities in the primary focus of acutely lesioned cats. The (Na+,K+)-ATPase catalytic subunits were resolved by SDS-gel electrophoresis and their phosphorylation levels were measured in presence of K+ ions and phenytoin. K+ was more effective in inducing maximal dephosphorylation of (Na+,K+)-ATPase in C57/BL, with identical affinity in the two strains. Phenytoin decreased the net phosphorylation level of (Na+,K+)-ATPase by about 50% in C57/BL mice, but only by 20% in DBA/2 mice. Both K+ and phenytoin dephosphorylating influences were decreased in primary and secondary foci of acutely lesioned cats. Those changes were limited to the alpha(-) subunit. In chronic cats, the dephosphorylating step of the (Na+,K+)-ATPase catalytic subunit recovered a normal affinity to K+, but its sensitivity to phenytoin remained decreased. Those differences in K+ and phenytoin influences on brain (Na+,K+)-ATPases between control and epileptic cortex might be responsible for the ictal transformation and seizure spread. In cats, the alteration of the alpha(-) isoform could mainly affect the glial cells.

Milacemide stimulates deficient glial Na+, K(+)-ATPase in freezing-induced epileptogenic cortex of cats

We investigated the influence of milacemide, a glycinamide derivative with putative antiepileptic activity, on the K(+)-activation of Na+,K(+)-ATPase in bulk isolated glial cells and synaptosomes of control and epileptogenic cortex of cats with a chronic freeze lesion. In the primary and secondary epileptic foci of non-treated animals, glial Na+,K(+)-ATPase lost its physiological K(+)-activation, while the synaptosomal enzyme was unchanged. These data reproduced previous work done on the kinetic measurement of the enzymic activities. In treated animals (500 mg/kg milacemide given orally for 2 weeks after the freeze lesion), the glial enzyme showed a normal K(+)-activation in the epileptic foci. These results confirm the existence of an abnormal glial Na+,K(+)-ATPase in cold-induced focal epilepsy and suggest that the antiepileptic activity of milacemide might be secondary to an activation of glial Na+,K(+)-ATPase, contributing to antagonize ictal transformation and seizure spread.

Effects of systemic kainic acid administration on regional Na+, K+-ATPase activity in rat brain

Changes in the activity of Na+,K+-ATPase and in the water, Na+, and K+ levels in the parietal cortex, hippocampus, and thalamus were investigated in rats 1, 3, 6, and 24 h following systemic kainic acid injection. An increase in Na+,K+-ATPase activity was observed in all three regions 3 h after the treatment, with a subsequent decrease in enzyme activity. The elevation in Na+,K+-ATPase activity was accompanied by an increase in the Na+ content and a decrease in the K+ content. These changes are presumed to occur because of repeated discharges and excessive prolonged depolarization in response to kainic acid. The decreases in Na+,K+-ATPase activity 6 and 24 h following kainic acid treatment coincide with neuropathological damage and edema formation, mainly in the hippocampus and thalamus.

The effect of vanadate on Na+,K+-ATPase activity of mouse cerebral cortex during bicuculline-induced seizures

The effect of bicuculline-induced seizures on Na+,K+-ATPase activity of mouse cerebral cortex homogenates, using two different procedures of sample preparation (freezing in situ or decapitation of animals without freezing) is described. Regardless of tissue treatment Na+,K+-ATPase activities during bicuculline-induced seizures did not differ significantly from the appropriate controls when vanadate-free ATP was used as substrate. The response of Na+,K+-ATPase to K+ activation was also similar; the increase in potassium concentration from 2 to 20 mM caused a 33.0 and 32.3% increase of enzyme activity in cortical homogenates from control and convulsing mice, respectively. Vanadate added to the assay medium inhibited Na+,K+-ATPase activity in a dose-dependent manner; with both types of tissue treatment there was, however, a tendency towards lesser inhibition of the enzyme from convulsing mice and at 1 X 10(-7) M vanadate this difference, though slight, was statistically significant: -22.59 vs -27.55% (freezing) and -28.73 vs -38.42% (decapitation) for seizures vs controls, respectively. The reduced sensitivity of Na+,K+-ATPase towards vanadate inhibition in cortical homogenates prepared from mice with convulsions suggests that vanadate might play a role in the modulation of enzyme activity during seizures in vivo.

Vanadate and brain adenylate cyclase. Effect of spreading depression

The effect of vanadate on the adenylate cyclase activity of rat cerebral cortex homogenates is described. In the absence of ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA), 10(-6)M vanadate inhibited enzyme activity by 23%, while 10 (-4) M and 10(-3) M stimulated the enzyme by 14 and 90%, respectively. In the presence of 0.2 mM EGTA, 10 (-6) M to 10(-3) M vanadate had only stimulating effects (18-450%). Additive effects of vanadate and noradrenaline on adenylate cyclase activity suggest different sites of action of these agents. Interaction of vanadate with both fluoride and guanyl-5'-yl imidodiphosphate had an apparently competitive character. Adenylate cyclase maximally stimulated by fluoride (10 mM) was inhibited by vanadate. This inhibitory effect was more pronounced in the absence of EGTA. Adenylate cyclase in the homogenates from the rat cerebral cortex in vivo invaded by spreading depression was slightly increased (up to 38%). This effect was abolished by low (10 (-7) M) vanadate. The results suggest that brain adenylate cyclase is stimulated by vanadate via the guanine nucleotide regulatory protein. The mechanism of vanadate's action, its modulation by calcium ions and the possible physiological role of these effects are discussed.

Na+ + K+-ATPase in serially excised segments of epileptic monkey cortex

The membrane-bound enzyme Na+ + K+-ATPase was measured in serially excised specimens of cerebral cortex in epileptic and control monkeys. Experimental chronic epileptic cortex showed significantly lower values than controls, as is seen in some other models and human epilepsy, but is different from the increased enzyme values in cobalt and freezing lesion epilepsy.

Absence of seizures or mirror foci in experimental epilepsy after excision of alumina and astrogliotic scar

In 15 rhesus monkeys (Macaca mulatta) made epileptic by the sensorimotor cortical injection of alumina, the roles of alumina and of "mirror foci" were investigated by serial surgical excisions of the granuloma, surrounding epileptic focus, and contralateral homotopic sensorimotor cortex. Electroencephalographic and electrocorticographic recordings documented foci and transmitted contralateral epileptic activity. After the granuloma was removed, seizures continued but without alumina. After the epileptic cortex was removed, no seizure activity remained and no contralateral independent foci occurred. These findings indicate that the epilepsy incident to alumina injection into the sensorimotor cortex in monkey is not dependent on the continual presence of alumina and is not associated with independent or "mirror foci."

Release of amino acids from chronic epileptic and subepileptic foci in vivo

Perforated discs of cobalt or nickel were implanted onto the sensorimotor strip of the cerebral cortex of rats. Co discs gave rise to myoclonic contralateral limb-jerks in a manner similar to Co powder lesions. In contrast, Ni-implanted animals were never observed to show overt limb-jerks. On superfusion with an in vivo cannula system, both types of lesion released increased amounts of glutamate, valine and glycine as compared with unlesioned tissue. However, the enhancement of release from epileptogenic Co lesions was approximately 3-fold greater than that from non-epileptogenic lesions. In addition, epileptogenic lesions showed a marked reduction in glutamine release compared to controls, while non-epileptogenic lesions did not. The possible involvement of local disorders of the glutamate/glutamine system in the generation of cobalt focus hyperactivity is discussed.

Potassium clearance and reactive gliosis in the alumina gel lesion

Potassium accumulation or impaired potassium clearance has been hypothesized to contribute to epileptogenesis in gliotic epileptogenic foci. To test this hypothesis, potassium clearance rates following direct cortical stimulation were measured in the cortex of monkeys rendered epileptic by the injection of alumina gel into the motor area. Reactive gliosis at the sites in which potassium clearance was measured was then quantitated histologically and compared with potassium clearance rates. Dense gliosis was associated with slowed potassium clearance, although the base-line potassium level appeared no different in actively epileptogenic areas or gliotic areas compared with normal areas. Possible mechanisms and significance of slowed potassium clearance in the alumina focus are discussed.

The effects of aliphatic alcohols on the biophysical and biochemical correlates of membrane function

The simplicity of the structure of aliphatic alcohols suggests that their interaction with receptors in the classical sense is unlikely. The actions of alcohols may involve a relatively nonspecific disruption of cell membranes, possibly physically dissolving into neuronal membranes especially, resulting in the malfunction of normal physiological processes. Studies of alcohol-membrane interactions have employed the use of artificial and nonneural membranes, invertebrate neurons for electrophysiological measurements and brain tissue for studying ion fluxes and enzymatic activities. For the most part these studies have been inclusive because high concentrations of alcohols were needed to elicit any effect. Also, it is difficult to extrapolate the data to in vivo mammalian systems, especially relative to the clinical signs of depression of the central nervous system.