The functional pathology of ion channels is involved to development of neuronal hyperexitability in brain. Voltage- and Ca2+-activated large-conductance K+ (BK) channels are widely expressed in neurons. In native tissue BK-channels are formed by heteromeric assembly of two distinct subunit components: the pore-forming α-subunit and regulatory β-subunit (β1- β4). BK-channel activation modulates of shaping action potentials by substantial contributing to their repolarization and fast after-hyperpolarization, pre-synaptic BK-channels selectively control of glutamate release. It is known that BK-channel activation is mediated by membrane potential, intracellular Ca2+ or α/β subunit composition. Presumably, BK-channels are critical for regulating neuronal excitability and, therefore, can contribute significantly to epilepsy pathophysiology. In this report, we studied the involvement of BK-channels to development and maintenance of neuronal hyperexcitability in dentate gyrus of Krushinskii-Molodkina rats (KM) prone to audiogenic seizures.
Using a Western blot method and specific antibody it was been shown that the level of pore-forming α-subunits (KCNMA1) in dentate gyrus of Wistar and KM rats did not differ. On the contrary, β4-subunit (KCNMB4) in dentate gyrus of KM rats increased in 2 times in comparison with Wistar ones. Besides, using a control antigen we demonstrated that β4-antibody specifically reacted agains two protein bands: 25-28 kDa (β4') and 16-18 kDa (β4''). Probably, β4' and β4'' are splising variants or its have different level of glycosylation. The levels of both proteins increased in dentate gyrus of KM rats: β4'- 180,66±13,11% (p<0,01) and β4'' – 257,47±53,40% (p<0,05) in comparison with Wistar ones. After chronic audiogenic seizures (20 convulsive fits) the level of β4' in dentate gyrus of KM rats was decreased to 30% from native KM ones, and β4'' - up to 42%. It is known that β4 containing BK channels have slow kinetics of activation / inactivation and its are insensitive to changes of membrane potential. Taken together, these data indicate the significant genetic changes in BK channel function in dentate gyrus of KM rats. We expect that increasing of β4 subunitin dentate gyrus of KM rats is a adaptive neurochemical mechanism, which may prevent the development of neuronal hyperexcitability in brain.
The study was supported by RFBR grant №12-04-00813.