Some factors affecting the diffusion of [14C]-lactate in human dental plaque.

The apparent diffusion rate, D, of lactate was significantly retarded in dental plaque fluid and a simulated plaque fluid consisting of a chemically-defined solution of salts, amino acids and albumin in phosphate buffer at pH 6.5. Metabolic utilization of lactate in live plaque residue reduced D for lactate into such samples of residue, compared with killed samples. D in plaque residue was lower than in a previous study. Increasing the packing density of killed plaque residue of Streptococcus sanguis cells reduced D. Pre-incubation of plaque residue with sucrose or sucrose + NaF reduced D for lactate. No such relationship was found when Streptococcus mutans was so treated, but D for lactate was lower when the cells were grown in tryptone-soy broth supplemented with 5 per cent sucrose compared with unsupplemented broth. The retardation of lactate increased with an increase in ion-exchange capacity of cation- and anion-exchange Sephadex gel-model systems. Thus, the apparent diffusion coefficient of lactate in dental-plaque residue is influenced by the chemical composition of the plaque aqueous phase, by metabolism of lactate, by plaque tortuosity, sucrose metabolism and ion-exchange interactions.