Lactate transport across sarcolemmal vesicles isolated from rainbow trout white muscle

Rainbow trout (Oncorhynchus mykiss) retain the majority of lactate produced during exhaustive exercise within white muscle. Previous studies have suggested that this retention is partially via a re-uptake of released lactate. The purpose of this work was to study lactate uptake using trout white muscle sarcolemmal vesicles. Lactate uptake by trout white muscle is partially through a low-affinity, high-capacity carrier (apparent K(m)=55.6 mmol l(-)(1) and V(max)=44.5 nmol mg(-)(1 )protein min(-)(1)). At high concentrations (20 and 50 mmol l(-)(1)), pyruvate partially (up to 39 %) inhibited lactate uptake, suggesting the involvement of a monocarboxylate carrier. The anion transport inhibitor 4-acetoamido-4'-isothiocyanstilbene-2,2'-disulphonic acid (SITS) and the monocarboxylate transport inhibitor (&agr;)-cyano-4-hydroxycinnamate (CHC) stimulated apparent lactate uptake. The model developed suggests that lactate is taken up by the vesicles, at least in part by a pyruvate-sensitive monocarboxylate carrier, and that its subsequent efflux is inhibited by SITS and CHC, suggesting that lactate export from trout white muscle is also carrier-mediated.