Pertussis toxin does not affect the time course of quantal release in crayfish and mouse muscle, but has other post- and presynaptic effects, especially on adenosine autoreceptors.

While G-proteins are involved in the synaptic release machinery and also can mediate inhibition of presynaptic Ca2+ channels, we find that pertussis toxin (PTX) does not affect the amount and the time course of quantal release from motor nerve terminals on crayfish or mouse muscle. Monoquantal excitatory currents (qEPSCs) were recorded that were elicited by constant depolarisation pulses to a terminal by means of a perfused macro-patch electrode. Although presynaptic effects of PTX on output and time course of release of quanta were absent, postsynaptically the rise time of qEPCs was increased and their decay time constant reduced. Adenosine (Ad) is known to inhibit quantal release in vertebrate motor nerve terminals via PTX sensitive G-proteins, and Ad is generated during nicotinic synaptic transmission by breakdown of the co-transmitter adenosine triphosphate (ATP). As reported by others, we found in mouse muscle inhibition of quantal release after application of Ad, but in addition late facilitation. Both these effects of Ad were blocked when the muscle was pre-incubated with PTX.