Fig. 3. Transport of cAMP and cGMP by the tubule are distinct processes. (A) cGMP and/or cAMP transport assays were performed on wild-type tubules in the absence (controls=100%) or presence of cyclic nucleotide (cAMP for cGMP transport; cGMP for cAMP transport) Percentage changes in the ratio of cGMP or cAMP transport compared to the controls are shown as mean ± s.e.m. (N5). Statistical significance was verified by Student's t-test compared with control (no added drugs), taking P<0.05 as the critical level. (B) cGMP and cAMP transport ratios from tubules assayed in either normal Drosophila saline (normal DS, unshaded bars) or minimal saline (shaded bars). (C) cAMP transport ratio from tubules assayed in either normal Drosophila saline (normal DS, unshaded bars); in minimal saline (shaded bar); or in minimal saline with additions of specific amino acids or other compounds as indicated (hatched bars). Data are mean ± s.e.m. (N5). ^***Data significantly different (P<0.001; Student's t-test) from cAMP transport ratio in normal DS.