Distribution of voltage-dependent calcium channel beta subunits in the hippocampus of patients with temporal lobe epilepsy.

Voltage-dependent Ca2+ channels constitute a major class of plasma membrane channels through which a significant amount of extracellular Ca2+ enters neuronal cells. Their pore-forming alpha1 subunits are associated with cytoplasmic regulatory beta subunits, which modify the distinct biophysical and pharmacological properties of the alpha1 subunits. Studies in animal models indicate altered expression of alpha1 and/or beta subunits in epilepsy. We have focused on the regulatory beta subunits and have analysed the immunoreactivity patterns of the beta1, beta2, beta3 and beta4 subunits in the hippocampus of patients with temporal lobe epilepsy (n = 18) compared to control specimens (n = 2). Temporal lobe epilepsy specimens were classified as Ammon's horn sclerosis (n = 9) or focal lesions without alteration of hippocampal cytoarchitecture (n = 9). Immunoreactivity for the beta subunits was observed in neuronal cell bodies, dendrites and neuropil. The beta1, beta2 and beta3 subunits were found mainly in cell bodies while the beta4 subunit was primarily localized to dendrites. Compared to the control specimens, epilepsy specimens of the Ammon's horn sclerosis and of the lesion group showed a similar beta subunit distribution, except for beta1 and beta2 staining in the Ammon's horn sclerosis group: in the severely sclerotic hippocampal subfields of these specimens, beta1 and beta2 immunoreactivity was enhanced in some of the remaining neuronal cell bodies and, in addition, strongly marked dendrites. Thus, hippocampal neurons apparently express multiple classes of beta subunits which segregate into particular subcellular domains. In addition, the enhancement of beta1 and beta2 immunoreactivity in neuronal cell bodies and the additional shift of the beta1 and beta2 subunits into the dendritic compartment in severely sclerotic hippocampal regions indicate specific changes in Ammon's horn sclerosis. Altered expression of these beta subunits may lead to increased currents carried by voltage-dependent calcium channels and to enhanced synaptic excitability.