ABSTRACT
BACKGROUND AND OBJECTIVES: Medial vestibular nucleus (MVN) neurons are second-order afferent neurons that are involved in the reflex control of the head and eyes. Results from several studies utilizing the intracellular microelectrode recording techniques suggest the presence of several ionic conductances contributes to the regulation of the MVN neuron excitability in rats. In this study, the types and characteristics of voltage-dependent potassium currents were investigated in acutely isolated MVN neurons of postnatal rats. Material and Methods: Electrophysiological recordings were performed by means of the whole cell patch clamp techniques. Coronal slice (400 nm) of the vestibular nucleus region was sequentially treated with pronase 0.2 mg/ml and thermolysin 0.2 mg/ml, then single neurons were mechanically dissociated RESULTS: In a Ca2+ -free solution, low-threshold transient (IA) and high-threshold sustained (IK) currents were recorded. IK was activated (gamma=4.0-12.4 ms at 10 mV) and inactivated (gamma=180-720 ms at 10 mV) more slowly than IA. The half-maximum activation and inactivation potential were -3.1+/-3.4 mV and -38.8+/-3.6 mV, respectively. IA was activated rapidly (gamma=1.0-2.3 ms at 10 mV) and inactivated in 10-60 ms. The half-maximum activation and inactivation potentials were -22.3+/-4.5 mV and -58.4+/-3.8 mV, respectively. When a 4-aminopyridine of 10 mM was applied, IA was almost totally blocked. In a solution with 2 mM Ca2+, calcium dependent potassium currents were identified by application of a Ca2+ free solution and consisted of a transient and a sustained components. Exposure to 0.3 nM apamin induced a reversible reduction of a sustained components. CONCLUSION: These results suggest that MVN neurons express a variety of voltage-dependent potassium currents which are responsible for proper membrane excitability and firing of MVN neurons.