Figure 5. Time course of butyrate uptake into pig colonic LMV in the presence and absence of an inward-directed pH gradient.

LMV were loaded with either 300 mm mannitol (•) or 100 mm mannitol and 100 mm of either sodium butyrate (▴) or NaHCO₃ (▪), 20 mm Hepes-Tris (pH 7.5) and 0.1 MgSO₄. LMV (100 μg protein per assay) were incubated in media containing 100 mm mannitol, 100 mm sodium gluconate, 20 mm Mes-Tris (pH 5.5; A) or 20 mm Hepes-Tris (pH 5.5; B), 0.1 mm MgSO₄ and 1 mm [U-¹⁴C]butyrate. Uptake was measured at 37 °C as described. Values are presented as the means ± s.e.m. for three experiments.