Effect of phenol on the ion currents of frog nerve ending.

The effect of phenol on the transmitter release was studied at the neuromuscular junction of a frog cutaneous pectoris muscle using the extracellular microelectrode technique. It was shown that phenol (0.5 mM) enlarged the quantal content of the end-plate currents (EPCs), and it caused the increase of duration of the second negative and third positive phases of the triphasic response observed experimentally. The amplitude of the third phase (outward K+ current) decreased, and one of the second phase was unchanged. The effect of phenol remained in the presence of the Ca(2+)-channel blockers (Co2+, Mn2+), and disappeared in the presence of the tetraethylammonium (TEA) and 4-aminopyridine (4-AP). The results suggest that phenol changes the kinetics of the voltage-dependent K+ current, which is one of the mechanisms of the phenol facilitating effect at the synaptic transmission.