The biochemistry of the neuron: methods and calculations for the analysis of neurotransmitter secretion from populations of single cells.

Methods and calculations for the continuous measurement of secretion of radiolabeled neurotransmitter from cultured neuronal cells are demonstrated. The method is used to measure the secretion of [3H]-norepinephrine by neuronally differentiated PC12 cells in response to a stepwise presentation of a depolarizing stimulus. The response is known to be biphasic, consisting of a transient burst of secretion (phase I) followed by a plateau of secretion (phase II). Habituation, in which cellular secretion is lowered by repetitive stimulation of the cells, is shown here to lower uniformly both phases of secretion. There thus appears to be a mechanism within the cell that holds constant the proportions of phase I and phase II secretion even though the overall size of the secretory response may be regulated as a consequence of repetitive stimulation. The feasibility of the method for widespread application to cultured neuronal cells is demonstrated.