Actions of potassium channel blockers on guinea-pig lateral olfactory tract axons

Population action potentials were recorded from the guinea-pig isolated lateral olfactory tract. At 30 degrees C, the conduction velocity of the fibres was about 4 m/s and the absolute refractory period was less than or equal to 1.5 ms. The population spike was unaffected by removal of calcium ions from the superfusate but was abolished in tetrodotoxin. Tetraethylammonium ions (10 mmol/l) had no effect on the population spike, however the following potassium channel blocking drugs increased the duration in a concentration-dependent manner (in order of decreasing potency): 3,4-diaminopyridine, 4-aminopyridine, 3-aminopyridine, sparteine, cesium ions and barium ions. In addition to a prolongation, these substances also reduced the amplitude of the conducted spike. It is concluded that the rising phase of the spike is generated by a voltage-dependent increase in sodium conductance and that an increase in potassium conductance contributes to the falling phase. The potassium channels are potently blocked by aminopyridine like drugs.