(R)-lactate(in) + citrate(out) = (R)-lactate(out) + citrate(in)
(r)-lactate(in) + citrate(out) = (r)-lactate(out) + citrate(in)
(R)-lactate(in) + citrate(out) = (R)-lactate(out) + citrate(in)
(r)-lactate(in) + citrate(out) = (r)-lactate(out) + citrate(in)