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

Abstract

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-ethyl-maleimide (MalNEt), 5,5-dithiobis-(2-nitrobenzoic acid) (Nbs₂), parachloro-mercuribenzoate (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.

Key Words:

• active transport
• carnitine
• cell culture
• dithiothreitol
• Girardi human heart cells