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J Neurophysiol 81: 140-148, 1999;
0022-3077/99 $5.00
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The Journal of Neurophysiology Vol. 81 No. 1 January 1999, pp. 140-148
Copyright ©1999 The American Physiological Society

Voltage-Activated K+ Currents of Hypoglossal Motoneurons in a Brain Stem Slice Preparation From the Neonatal Rat

Remigijus Lape and Andrea Nistri

Biophysics Sector and Istituto Nazionale Fisica della Materia Unit, International School for Advanced Studies, 34013 Trieste, Italy

Lape, Remigijus and Andrea Nistri. Voltage-activated K+ currents of hypoglossal motoneurons in a brain stem slice preparation from the neonatal rat. J. Neurophysiol. 81: 140-148, 1999. Whole cell, patch-clamp recordings were performed on motoneurons of the hypoglossus nucleus in a brain stem slice preparation from the neonatal rat brain. The aim was to investigate transient outward currents activated by membrane depolarization under voltage clamp conditions. In a Ca2+-free medium containing tetrodotoxin and Cs+, depolarizing voltage commands from a holding potential of -50 mV induced slow outward currents (Islow) with 34 ± 6 ms (SE) onset time constant at 0 mV and minimal decline during a 1 s pulse depolarization. When the depolarizing command was preceded by a prepulse to -110 mV, the outward current became biphasic as it comprised a faster component (Ifast), which could be investigated in isolation by subtracting the two sets of records. Ifast showed rapid kinetics (9 ± 4 ms 10-90% rise time and 70 ± 20 ms decay time constant at 0 mV) and strong voltage-dependent inactivation (half inactivation was at -92.9 ± 0.2 mV) from which it readily recovered with a biexponential timecourse (4.4 ± 0.6 and 17 ± 2 ms time constants at -110 mV membrane potential). Islow was selectively blocked by TEA (10-30 mM) while Ifast was preferentially depressed by 2-3 mM 4-aminopyridine. Analysis of tail current reversal indicated that both Islow and Ifast were predominantly due to K+ with minor permeability to Na+ (92/1 and 50/1, respectively). These results suggest that membrane depolarization activated distinct K+ conductances that, in view of their largely dissimilar kinetics, are likely to play a differential role in regulating the firing behavior of hypoglossal motoneurons.




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