Fig. 3. Calcium oxalate loading experiments in the anterior sternal epithelium of Porcellio scaber during late premoult. (A) Intensity signal in the loading medium at a Ca²⁺ activity (a_Ca) of 0.68 µmol l^-1. The intensity units given in A—C represent the difference between the mean grey-scale value and that in the first image. Each point represents the mean ± S.E.M. of nine animals. (B) Effect of ATP on calcium oxalate loading. After removal of Na₂ATP, calcium oxalate loading is immediately and reversibly blocked. (C) Effect of the specific smooth endoplasmic reticulum Ca²⁺-ATPase inhibitor cyclopiazonic acid (CPA) on calcium oxalate loading at a a_Ca of 0.38 µmol l^-1. After addition of 1 µmol l^-1 CPA, the increase in the intensity signal is immediately blocked. (D) Effect of a_Ca on calcium oxalate loading in the anterior sternal epithelium from late premoult animals. Each data point gives the mean intensity value (± S.E.M.) of 4-6 loading experiments. The rates were normalised to the highest rate at a a_Ca of 2.05 µmol l^-1 and plotted against a_Ca. The line was drawn using GraphPad Prism 3.0 software.

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