Effects of notexin on neuromuscular transmission in the guinea pig vas deferens.

The effects of notexin on neuromuscular transmission in the isolated vas deferens of the guinea pig have been investigated using intracellular recording techniques. The toxin had no effect on the resting membrane potential, the amplitude or frequency of spontaneous excitatory junctional potentials or on the time constant of the decay of the evoked excitatory junctional potential in the smooth muscle cells. The amplitude of the evoked excitatory junctional potential was selectively reduced in the presence of notexin. The reduction in amplitude lasted for 20-30 min. Recovery occurred despite the continued presence of the toxin. Once recovery had been achieved the preparation remained insensitive to further exposure to the toxin. Although the amplitude of excitatory junctional potentials recovered in the continued presence of notexin, facilitation remained depressed. Action potentials, when generated, were indistinguishable from those in control tissues. It is concluded that notexin is a presynaptic inhibitor of transmission in the guinea pig vas deferens.