Modulation of inhibitory post-synaptic currents (IPSCs) in mouse cerebellar Purkinje and basket cells by snake and scorpion toxin K+ channel blockers

1 Using an in vitro mouse cerebellar slice preparation and whole-cell electrophysiological recording techniques we have characterized Purkinje and basket cell inhibitory post-synaptic currents (IPSCs), and examined the effects of a number of selective peptidergic K+ channel blockers. 2 Spontaneous IPSC amplitude ranged from similar to 10 pA up to similar to 3 nA for both cell types [mean values: Purkinje cells -122.8+/-20.0 pA (n=24 cells); basket cells -154.8+/-15.9 pA (n=26 cells)]. Frequency varied from similar to 3 up to similar to 40 Hz, [mean values: basket cells 14.9+/-1.7 Hz (n=26 cells); Purkinje cells 17.9+/-2.2 Hz (n=24 cells)]. 5 mu M bicuculline eliminated virtually all spontaneous currents. 3 IPSC rise times were fast (similar to 0.6 ms) and the decay phase was best fit with the sum of two exponential functions (tau(1) and tau(2): similar to 4 ms and similar to 20 ms, n=40; for both cell types). 4 The snake toxins alpha-dendrotoxin (alpha-DTX) and toxin K greatly enhanced IPSC frequency and amplitude in both cell types; the closely related homologues toxin I and gamma-dendrotoxin (gamma-DTX) produced only marginal enhancements (all at 200 nM). 5 Two scorpion toxins, margatoxin (MgTX) and agitoxin-2 (AgTX-2) had only minor effects on IPSC frequency or amplitude (both at 10 nM). 6 Low concentrations of tetraethylammonium (TEA; 200 mu M) had no overall effect on cerebellar IPSCs, whilst higher concentrations (10 mM) increased both the frequency and amplitude. 7 The results suggest that native K+ channels, containing Kv1.1 and Kv1.2 channel subunits, play an influential role in controlling GABAergic inhibitory transmission from cerebellar basket cells.