ACTION OF ALPHA-DENDROTOXIN ON K-TERMINAL REGIONS OF AXONS IN RAT OLFACTORY CORTEX( CURRENTS IN NERVE)

1 In the rat olfactory cortex, unmyelinated axons give rise to synapse s en passant. This tissue was used to study the pharmacology of axonal K+-currents. Responses were measured from a group of these axons as u nclamped field currents, with a polarizable suction electrode. 2 A sin gle stimulus to the axons elicited a tetrodotoxin-sensitive Na+-depend ent transient. K+-currents were revealed by positive polarization of t he suction electrode and were manifest as a negative current following the Na+-component. 3 In the presence of tetraethylammonium (TEA, 5 mM ) and Cd2+ (100 muM), the K+ -component was depressed by 3,4-diaminopy ridine (3,4-DAP; 1 to 20 muM; IC50 2.0 +/- 0.4 muM). Alpha-dendrotoxin (DTX; 15-1500 nM) also attenuated the aminopyridine-sensitive compone nt (IC50 93 +/- 4 nM). At the highest DTX concentration, depression of the K+-current was incomplete, the residual K+ current being reduced by 3,4-DAP (0.1 to 5 muM). 4 These results indicate the presence of tw o aminopyridine-sensitive K+ currents in this preparation distinguishe d by their susceptibility to DTX.