Fig. 5. Transepithelial flux of Texas Red as a function of bathing saline Texas Red concentration for Drosophila tubules set up in Ramsay assays. Each point shows the mean ± S.E.M. for N=7–30 tubules. The solid line represents the fit to the Michaelis–Menten equation by non-linear regression analysis. The inset shows the ratio of the concentration of Texas Red in the secreted fluid to that in the bathing medium (S/M) as a function of bathing medium Texas Red concentration. As discussed in the text, the point at 50 µmol l^–1 Texas Red was excluded from the curve-fitting procedure.