Читать книгу Canine and Feline Epilepsy - Luisa De Risio - Страница 13

Functional and perhaps structural changes occur in the postsynaptic membrane, thus altering the character of receptor protein-conductance channels, thereby favouring development of paroxysmal depolarizing shifts (PDS) and enhanced excitability. Epileptic neurons appear to have increased Ca2+ conductance. It may be that latent Ca2+ channels are used, that the efficacy of Ca2+ channels is increased or that the number of Ca2+ channels is chronically elevated. However, development of burst activity depends on the net inward current and not on the absolute magnitude of the inward current. When extracellular K+ concentrations are increased (as during seizure activity), the K+ equilibrium across the neuronal membrane is reduced, resulting in reduced outward K+ currents. The net current will become inward, depolarizing the neuron to the extent that Ca2+ currents will be triggered. This results in a PDS and a burst of spikes (Dichter and Ayala, 1987).