Developmental profile of spontaneous transient outward currents in rat medial vestibular nucleus

Abstract

Using whole-cell patch-clamp method, spontaneous transient outward currents (STOCs) were found in a subgroup of neurons within medial vestibular nucleus (MVN). These outward currents were resistant to tetrodotoxin, CNQX, AP-5, strychnine and gabazine but mostly abolished by bicuculline that can inhibit small-conductance calcium-activated potassium (SK) channel. Apamin, a specific blocker of SK channel, can completely eliminate these STOCs while 1-EBIO, a SK channel opener, can facilitate these outward currents, which proved that these outward currents were mediated by SK channels. Both Cd2+-containing and Ca2+-free solutions partially reduced the frequency of STOCs, suggesting that calcium influx was essential to generate STOCs. On the other side, calcium from cytoplasmic calcium store was also required for initiating STOCs as ryanodine diminished the STOCs whereas caffeine (100 µM) enhanced the frequency of STOC. The frequency and amplitude of these SK channel-mediated STOCs were both increased from Postnatal day (P)1 to P21. Taken together, these outward currents required both external and internal calcium resources to activate SK channels and provided a novel inhibitory function beside GABAergic/glycinergic transmission during development. (Supported by NSFC/RGC N_HKU735/14)