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

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Abstract
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 ∼10 pA up 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 ∼3 up 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 μm bicuculline eliminated virtually all spontaneous currents. IPSC rise times were fast (∼0.6 ms) and the decay phase was best fit with the sum of two exponential functions (τ1 and τ2: ∼4 ms and ∼20 ms, n = 40; for both cell types). The snake toxins alpha‐dendrotoxin (α‐DTX) and toxin K greatly enhanced IPSC frequency and amplitude in both cell types; the closely related homologues toxin I and gamma‐dendrotoxin (γ‐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 μm) 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. British Journal of Pharmacology (1998) 125, 1375–1381; doi:10.1038/sj.bjp.0702218