Voltage-gated and background K+ channel subunits expressed by the bushy cells of the rat cochlear nucleus

Bushy cells of the ventral cochlear nucleus produce a single, short latency action potential at the beginning of long depolarisations. In the present work an immunochemical survey was performed to detect the presence of K+ channel subunits which may contribute to the specific membrane properties of the bushy cells. The immunocytochemical experiments conducted on enzymatically isolated bushy cells indicated positive immunolabelling for several subunits known to be responsible for the genesis of rapidly inactivating K+ currents. Bushy cells showed strong expression of Kv3.4, 4.2 and 4.3 subunits, with the lack of Kv1.4 specific immunoreaction. The Kv3.4-specific immunoreaction had a specific, patchy appearance. Bushy cells also expressed various members of the Kv1 subunit family, most notably Kv1.1, 1.2, 1.3 and 1.6. Weak positivity could be observed for Kv3.2 subunits. The positive immunolabelling for Kv3.4, Kv4.2 and Kv4.3 was confirmed in free-floating tissue slices. Voltage-clamp experiments performed on positively identified bushy cells in brain slices corroborated the presence and activity of Kv3.4 and Kv4.2/4.3 containing K+ channels. Bushy cell showed strong immunopositivity for TASK-1 channels too. The results presented in this work indicate that bushy cells possess several types of voltage-gated K+ channel subunits whose activity may contribute to the membrane properties and firing characteristics of these neurones.