Demonstration of two distributions of vesicle radius in the dopamine neuron of Planorbis corneus from electrochemical data

An electrochemical model to calculate the relative size and neurotransmitte r concentration of individual nerve cell vesicles is presented to examine p otentially different types of vesicles in Planorbis corneus. Amperometric c urrent transients resulting from individual exocytosis events detected from single cells contain the information necessary to quantify vesicular neuro transmitter amount and to estimate other important cellular properties such as vesicular neurotransmitter concentration and vesicle radius. Use of a s implifying assumption that the cross-sectional area of the contents of each release event is the apparent electroactive area of the electrode and that the shape of the decreasing phase of each current transient follows Cottre ll-like behavior, the Cottrell equation and Faraday's law can be combined t o yield expressions for relative vesicle radius and neurotransmitter concen tration. This analysis has been applied to data obtained from the cell body of the giant dopamine neuron of the pond snail P. corneus. The histogram o f vesicular dopamine concentration reveals a single wide distribution and t he histogram of vesicle radius reveals a bimodal radius distribution. These data strongly suggest two distinct classes of vesicle radius in the P. cor neus neuron lead to the bimodal distribution of amount released reported ea rlier. (C) 1999 Elsevier Science B.V. All rights reserved.