Components of the synaptic current of rat submandibular ganglion cells

1. Cells of the rat submandibular ganglion have been studied in vitro by means of a two-microelectrode voltage clamp technique. 2. Stimulation of preganglionic nerve fibres evokes an inward synaptic current which decays in a bi-exponential fashion. Fast and slow components have similar reversal potentials, and both time constants are prolonged by hyperpolarizing the cell. 3. Analysis of the current fluctuations occurring when acetylcholine (ACh) is applied to the cell shows that the spectrum contains two Lorentzian components, whose time constants correspond to those of synaptic currents. 4. Relaxations of inward current following a step change in membrane potential in the presence of ACh also reveal two exponential components. Varying the ACh concentration does not affect their time constants or relative amplitude. 5. Miniature synaptic currents usually show only the fast component. Reducing the quantal content of the evoked synaptic current by lowering [Ca2+] does not affect the relative amplitude or the time constants of the two components. 6. Analysis of the fluctuations in amplitude of the slow and fast components during a train of synaptic currents shows that the two amplitudes are weakly but significantly correlated. 7. It is concluded that the ganglion cells possess two types of ACh receptor, controlling channels of different mean lifetime. Quanta released by nerve stimulation tend to act on one or other type of receptor, but a significant proportion of quanta reach both types of receptor.