Fig. 1. Michaelis-Menten analysis of dopamine uptake in isolated snail brains measured by rotating disk electrode voltammetry. Sequential addition of dopamine to the preparation showed a K_m of 0.9 µmol l^-1 dopamine and a V_max of 558 pmol dopamine s^-1 g^-1 wet mass. A total of 40 animals was used for this experiment (N=8; 5 pooled brains used for each experiment). Because the concentration of outside dopamine ([dopamine]_o) varied slightly as a function of the rate of uptake when each sequential addition of exogenous dopamine was made, individual data points are shown rather than averaged data. The data were fitted to the Michalis-Menten equation using non-linear regression. The curve does not significantly deviate from the model (P=0.36 via the runs test).