Abstract
We identified apamin-sensitive Ca dependent K currents (IKCa) and 3 types of voltage dependent K currents in median raphe neurons (MRNSs) of 0- to 24- days old rats. Potassium currents were recorded in MRNs of 150 to 200 μm thick brainstem slices from rats anesthetized with ketamine hydrochloride (1-2 mg) using whole-cell patch clamp method. Recorded neurons were injected with Lucifer yellow and identified as MRNs by use of anti-5HT antibodies conjugated with Texas red. Voltage dependent K currents (delayed rectifier K current- IKDR, transient K current- IA, 4AP-insensitive transient K current-IKt) were recorded in TTX (1μM) containing Ca2+-free solution. IKDR was sustained by depolarizing voltage commands with a prepulse of -90 to -50 mV (200 ms duration) and sensitive to 20 mM TEA. IA was identified by subtraction of IKDR from outward currents induced by depolarizing voltage commands with a prepulse of -90 to -150 mV (200 ms duration) and sensitive to 2-5 mM 4-AP. IKt was a slowly inactivating current sensitive to low concentration of TEA (≤3mM) but not to 4-AP. IKCa was identified as apamin (300 nM) sensitive outward current. The current densities of these K currents increased during postnatal maturation (0 to 24 days after birth); 40 to 80 A/F (IKDR), 30 to 100 A/F (IA), 40 to 70 A/F (IKCa). The postnatal developmental changes of K currents were coincident with those of spike duration and afterhyperpolarization in rat MRNs. [Jpn J Physiol 54 Suppl:S158 (2004)]
