Excitation of cutaneous sensory nerve endings in the rat by 4-aminopyridine and tetraethylammonium

1. The effects of the potassium channel blockers 4-aminopyridine (4-AP) and tetraethylammonium (TEA) on cutaneous sensory nerve endings have been investigated with the use of an in vitro skin-nerve preparation from the rat. 2. Direct application of these compounds to the nerve endings, but not to the axons, induced continuous discharges in most A beta, A delta, and C fibers. There was no relationship between the fibers' responsiveness or the threshold concentration required to induce discharges and either the conduction velocity or sensory properties of the fibers. 3. The rate of induced discharges increased linearly with increasing concentrations of 4-AP. At threshold concentrations of 10(-6)-10(-5) M, low-frequency, irregular discharges developed; but at the highest concentration of 10(-3) M, a characteristic doublet or bursting discharges usually emerged. 4. During and after the induced discharges there did not appear to be an alteration in the sensitivity of the sensory nerve endings to mechanical or thermal stimuli. 5. It is concluded that the induced activity arises from an action of these potassium channel blockers at or near the action potential generator region at the nerve endings.