SINGLE VOLTAGE-GATED K-ROOT GANGLION NEURONS OF RAT( CHANNELS AND THEIR FUNCTIONS IN SMALL DORSAL)

1. Single voltage-activated K+ channels were investigated by means of the patch-clamp technique in small dorsal root ganglion (DRG) neurones in 150 mu m thin slices of new-born rat DRG. It was found that K+ con ductance in small DRG neurones is formed by one type of fast inactivat ing A-channel and four types of delayed rectifier K+ channels, which c ould be separated on the basis of their single-channel conductance, ki netics and sensitivity to external tetraethylammonium (TEA). 2. Potass ium A-channels were observed at relatively moderate density They were weakly sensitive to TEA and activated between -70 and +20 mV. The cond uctance of A-channels was about 40 pS for inward currents in symmetric al high K+ solutions with external 5 mM TEA added to suppress other ty pes of K+ channels. The time constant of channel inactivation (tau(in) ) was 18.8 ms at -70 mV and 6 ms at potentials positive to -20 mV. 3. A fast delayed rectifier (DR(F)) channel with a conductance of 55 pS i n symmetrical high-K+ solutions was the most frequent type of K+ chann el. The channel activated in a broad potential range between -50 and 60 mV and demonstrated a fast deactivation within 1-3 ms after potenti al return to -80 mV in high-K-o(+) solution. The tau(in) value was 90- 150 ms at positive membrane potentials. The single-channel current amp litudes were blocked to 55% by 1 mM TEA. 4. Three further types of del ayed rectifier K+ channels were called DR(1)-, DR(2)- and DR(3)-channe ls. Their single-channel conductances for inward currents in symmetric al high-K+ solutions were distributed between 30 and 44 pS. The channe ls activated in almost the same voltage range between -60 and -10 mV. Deactivation of the channels at -80 mV lasted tens of milliseconds. Th e channels were separated on the basis of their sensitivities to TEA. DR(1)-channel currents were reduced to 50% in the presence of 1 mM TEA , DR(2)-channel currents were reduced to about 50% by 5 mM TEA, wherea s the amplitudes of currents through DR(3)-channels were almost unaffe cted by 5 mM TEA. 5. Addition of external 1 and 5 mM TEA to whole cell s under current-clamp condition depolarized the cell membrane, lowered the threshold for action potential firing, prolonged action potential duration and reduced the amplitude of after-hyperpolarization. 6. It is concluded that potassium A-, DR(F)-, DR(1), DR(2)- and DR(3)-channe ls play multiple roles in the excitability of DRG neurones. Possible i nfluences of these channels on the shape of the action potential, its firing threshold and the resting membrane potential of small DRG neuro nes are discussed.