The mode of action of guanidine on mouse motor nerve terminals.

The action of guanidine on presynaptic membrane currents has been investigated to elucidate its facilitatory effect on phasic transmitter release at the mouse neuromuscular junction. Guanidine (2-10 mM) produced a near complete inhibition of the fast voltage-dependent K current. This effect is expected to allow an increase in Ca2+ influx and, thereby, in transmitter release upon nerve stimulation. Guanidine failed to block the Ca-dependent K current of the nerve terminals.