The diffusional and osmotic water permeability of the hindgut cuticle in larval Sarcophaga bullata

The diffusional water permeability (P_D) and the pressure filtration coefficient (L_P) of isolated larval hindgut cuticle of the fleshfly, Sarcophaga bullata, were measured using tracer techniques coupled with a simple mathematical model system based on equations of non-equilibrium thermodynamics. Data obtained from the model system were matched to experimental tracer data by means of a mathematical optimization scheme. The following parameter values were obtained: P_D for tritiated water = 1.02 × 10^?6 cm-sec^?1, and L_P = 9.18 × 10^?11 cm³-dyn^?1-sec^?1. These results are now being used to determine reflection coefficients (σ's) and solute mobilities (ω's) for the cuticle system in an attempt to gain an understanding of the mechanisms controlling solute and water movements across the hindgut wall.