Presynaptic control of synaptic channel kinetics in sympathetic neurones

The kinetic properties of synaptically activated ion channels are an important determinant of the duration of the synaptic currents that produce postsynaptic potentials in autonomic neurones and skeletal muscle. In the two types of principal neurones in frog sympathetic ganglia, B and C cells, a twofold difference in the mean open time of the nicotinic acetylcholine (ACh-gated) ion channels accounts for the twofold difference in the decay rate of their fast excitatory postsynaptic currents (e.p.s.cs). The B and C cells are selectively innervated by two distinct classes of cholinergic preganglionic axons called B and C fibres, respectively. The present study examined the influence of the preganglionic nerve on the expression of synaptic ion channel properties in sympathetic neurones. B cells were denervated surgically and allowed to become innervated solely by preganglionic C fibres. These B cells, innervated by C fibres, acquired slowly decaying e.p.s.cs and long channel open times, characteristics normally seen in C cells only. These findings provide the first evidence that the kinetic properties of postsynaptic channels can be determined by the particular class of axon innervating a neurone.