Fig. 2.

Concentration gradients along ST of the guinea pig following 2- to 3-hour applications to the RWM. Distances are measured along the ST from the basal end. Results are shown for the marker ion TMPA [34], gentamicin [53] and dexamethasone [54]. In addition to the steep concentration gradients, it is also apparent that the basal turn (0–2 mm) concentrations of each substance vary by more than a factor of 10, due to inter-animal variations in RWM permeability and elimination of the drug. Recently, it has been shown that these concentration gradients are stable with time [83].