Fig. 4. Unidirectional secretory, unidirectional reabsorptive, and net urate fluxes by chick PTCs following treatment with methotrexate (500 µmol l^–1) or MK571 (20 µmol l^–1). Methotrexate (at t=–0.5 h) and MK571 (at t=0) were added to the interstitial or luminal sides of the epithelium. Data are presented as the percentage of the paired control secretory flux and are means ± S.E.M. of five preparations. ^*Significantly different from paired control flux (P<0.05, paired t-test).