Figure 2. Effect of in vitro culture on L-lysine influx in placental explants.

L-Lysine influx in either fresh or cultured explant of villous tissue over a 30 s period was measured in a medium containing 2 μM L-[³H]lysine (2 μCi ml⁻¹ or 74 KBq ml⁻¹) with or without unlabelled amino acid (100 μM for L-leucine or 2 mm for L-lysine, final concentration) in the presence or absence (choline) of Na⁺ as described in Methods. Data show carrier-mediated influx rate defined by subtracting the diffusional component from the total influx in either the presence or absence of Na⁺. The diffusional component was determined by measuring the influx of L-[³H]lysine in the presence of 20 mm unlabelled L-lysine. Data represent the mean ± s.d. of three separate experiments from three placentae. The mediated L-leucine-sensitive fluxes in the presence of Na⁺ in fresh and in cultured tissue are, respectively, 3.66 ± 0.61 and 9.49 ± 1.24 pmol (mg protein)⁻¹ (30 s)⁻¹. These are significantly different (P = 0.026). The mediated L-leucine-insensitive fluxes in the presence of Na⁺ in fresh and in cultured tissue are, respectively, 0.95 ± 0.21 and 3.01 ± 0.01 pmol (mg protein)⁻¹ (30 s)⁻¹. These are significantly different (P = 0.014).