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

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. Spontaneous IPSC amplitude ranged from approximately 10 pA up to approximately 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 approximately 3 up to approximately 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 microM bicuculline eliminated virtually all spontaneous currents. IPSC rise times were fast (approximately 0.6 ms) and the decay phase was best fit with the sum of two exponential functions (tau1 and tau2: approximately 4 ms and approximately 20 ms, n=40; for both cell types). 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). Two scorpion toxins, margatoxin (MgTX) and agitoxin-2 (AgTX-2) had only minor effects on IPSC frequency or amplitude (both at 10 nM). Low concentrations of tetraethylammonium (TEA; 200 microM) had no overall effect on cerebellar IPSCs, whilst higher concentrations (10 mM) increased both the frequency and amplitude. 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.