Discrimination between descriptive models of L-glutamate uptake by the retina using non-linear regression analysis

1. The uptake of labelled L-glutamate by the isolated rat retina was measured over a large range of external concentrations (1 micron to 1 mM). 2. The results obtained from measurements of the initial velocity of L-glutamate uptake at different concentrations did not follow simple hyperbolic kinetics. 3. The error structure of replicate velocity measurements was examined and found to be normally distributed and heteroscedastic. 4. Descriptive models were fitted directly to data, weighted by the invariance, using non-linear regression analysis. 5. The most suitable suitable descriptive model consisted of a saturable hyperbola (Vm = 285 n-mole.(g wet wt.)-1.min-1, Km = 252 micron) and a linear term (b = 0.45 min-1).