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°C, the conduction velocity of the fibres was about 4 m/s and the absolute refractory period was ≤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 concentrationdependent 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. [ABSTRACT FROM AUTHOR]