The effect of sulfhydryl blocking agents on the uptake of L-carnitine in an established human cell line (CCL 27).

The effect of sulfhydryl blocking agents on the active transport of L-carnitine into cells from an established cell line from human heart was studied. N-ethylmaleimide (MalNEt), 5,5-dithiobis-(2-nitrobenzoic acid) (Nbs2), parachloromercuribenzoate (ClHgBzO-) and cystamin all reduced the uptake of L-carnitine considerably. This was not due to a general membrane injury as judged by the trypan blue dye exclusion test. The inhibition caused by N-ethylmaleimide was irreversible, while that of Nbs2, ClHgBzO- and cystamin could be reversed by dithiothreitol. Excess L-carnitine in the medium exerted a small protective effect against the inhibition of Nbs2, but had no effect against the inhibition of the other agents. Neither could ClHgBzO- protect the uptake mechanism against the irreversible inhibition of N-ethylmaleimide. We conclude that the observations reflect the existence of a multitude of different SH-groups, and that some of these are essential for the cellular uptake of L-carnitine.