You will see that this greatly affects the rising phase of the curve. This parameter is often significant for the fall-off phase of the curve. In slice, we often find our data is well fit by about a 50 m radius, not far from the distance between our bipolar electrodes. You will need to experiment to find the best fit for your own parameters. A tutorial on this subject is on the GraphPad web site .
Higher values reflect a better fit.
Justin Lee from Synaptosoft has written a computer program that automates this simulation. The algorithm has been incorporated into an analysis program called 'Mini Analysis Program'. In the 'random walk menu' you can choose values for 4 parameters, which are the 'dead radius', initial transmitter concentration, Vmax and Km, and generate a curve in either amperometric or cyclic voltammetry mode. The size of the release area and the diffusion coefficient can be changed.