Effects of hycanthone on the neuromuscular transmission

The effects of the antischistosomal drug, hycanthone, on the synaptic transmission at the frog neuromuscular junction were studied. The mean quantal content increased in the presence of 20 microM hycanthone. The amplitude of the miniature end-plate current was unaffected by 20 microM hycanthone, while 2 microM hycanthone decreased the ionophoretic ACh response (ACh induced current). The decay time constants of the evoked end-plate current and the miniature end-plate current were increased with 1-5 microM hycanthone, but were decreased at concentrations over 20 microM. Analysis of the ACh induced noise revealed that 1 microM hycanthone slightly increased the channel lifetime whereas the single channel conductance was not affected. It was concluded that the primary site of action of hycanthone is the 'transient state' or ACh bound but closed conformation of the ACh receptor ion channel, but this drug also has other sites of action (presynaptic nerve terminal and open conformation of ACh receptor-ion channel complex).