Figure 4. Effect of extravesicular medium pH on butyrate uptake into human and pig colonic LMV.

The LMV were loaded with the standard loading buffer containing 100 mm mannitol, 100 mm sodium butyrate, 0.1mm MgSO₄ and 20 mm Hepes-Tris (pH 7.5). LMV (100 μg of protein per assay) were incubated in media containing 100 mm mannitol, 100 mm sodium gluconate, 0.1 mm MgSO₄, 1 mm [U-¹⁴C]butyrate and 20 mm Hepes-Tris, for pH 7.0, 7.5 and 8.0 or Mes-Tris for pH 5.5, 6.0 and 6.5. Initial rate of butyrate uptake was measured as described in Methods, at 37 °C for 5 s. Values are presented as the means ± s.e.m. for three experiments.