Table 2.

Effect of intravesicular anions on l-lactate uptake

Intravesicular anion	l-Lactate uptake (pmol (mg protein)−1 (5 s)−1)
	Pig colonic LMV	Human colonic LMV
No anion (mannitol)	114 ± 5	121 ± 5
l-Lactate	330 ± 19*	281 ± 17*
Butyrate	282 ± 11*	245 ± 10*
Propionate	259 ± 9*	n.d.
Acetate	248 ± 7*	n.d.
Bicarbonate	275 ± 10*	269 ± 12*
Chloride	189 ± 10*	n.d.
Sulphate	154 ± 5*	n.d.
Succinate	123 ± 1	n.d.
Gluconate	122 ± 3	n.d.

LMV were isolated as described in Methods. Vesicles were preloaded with 20 mm Hepes-Tris pH 7.5, 0.1 mm MgSO₄, and 300 mm mannitol or with 100 mm mannitol and 100 mm of the following sodium salts: gluconate, HCO₃⁻, SO₄₂₋, succinate, l-lactate, butyrate, Cl₋, acetate, or propionate. Membrane vesicles (100 μg of protein per assay) were incubated in the standard uptake buffer containing 100 mm mannitol, 100 mm sodium gluconate, 20 mm Mes-Tris pH 5.5, 0.1 mm MgSO₄ and 0.1 mml-[U-¹⁴C]lactate. Uptake was measured at 37 °C as described in Methods. The reaction was stopped after 5 s by the addition of 1 ml ice-cold stop buffer (100 mm mannitol, 100 mm sodium gluconate, 20 mm Hepes-Tris pH 7.5, 0.1 mm MgSO₄ and 0.1 mm sodium l-lactate) and samples were filtered under vacuum. Values are presented as means ±s.e.m.for three experiments. n.d. not determined.

^*Statistically significant, P < 0.05 from control (mannitol loaded).