At different levels of the holding potential on neuron R2 membrane in the Aplysia depilans abdominal ganglion, dopamine injected intracellularly increases the amplitude of both inward and outward currents recorded in response to the application of acetylcholine (ACh) to the ganglion surface. 2. The addition of dopamine to the external perfused solution produces generation of inward currents and a decrease in the cell response to the ACh. 3. The enhancing effect of injected dopamine on ACh responses is retained after inhibition of acetylcholinesterase (AChE) by a specific organophosphorous inhibitor, compound Gd-42. 4. The modulating effect of injected dopamine on ACh responses is discussed in terms of the existence of intracellular receptors of neurotransmitters in the differentiated cells.
