Fig. 6. KNK437-sensitivity of zinc-induced change in active cerebrospinal fluid-to-blood (CSF-to-blood) [¹⁴C]2,4-dichlorophenoxyacetic acid (2,4-D) fluxes across paired halves of shark IVth choroid plexus in the absence of trimethylamine oxide (TMAO). Fluxes of 2,4-D were determined after tissues were exposed at 13.5°C, ± 100 µmol l^–1 KNK437 (vehicle control was 0.2% DMSO), to treatment as follows. Zinc-treated, 6 h in 50 µmol l^–1 ZnSO₄ + 1.5 h recovery in L-15E (N=8); Control, 6 h in zinc-free medium + 1.5 h recovery in L-15E (N=7). Tabulated data show the mean unidirectional fluxes from which net data were derived. B to C, blood-to-CSF flux; C to B, CSF-to-blood flux. Data are means ± s.e.m.; ^*P<0.05 vs net flux in paired tissue treated without KNK437.