A possible role for glyceraldehyde transport in the stimulation of HIT-T15 insulinoma cells

Abstract

D-Glyceraldehyde was transported into HIT-T15 cells at a linear rate for approx. 2 min and appeared to be unsaturable up to a concentration of 50 mM. Evidence was obtained for an electrogenic component of uptake of the triose. The rate of D-glyceraldehyde transport was also reduced in the absence of Na+, suggesting that a component of uptake was Na(+)-linked. Transport of D-glyceraldehyde could be prevented by N-ethylmaleimide but not significantly by p-chloromercuribenzenesulphonic acid, L-glyceraldehyde, nor by a number of inhibitors of known transport systems. However, D-glyceraldehyde transport was inhibited by alpha-cyano-4-hydroxycinnamate, an inhibitor of some anion transport systems. D-Glyceraldehyde caused a marked depolarization of HIT-T15 cells accompanied by a rise in cytosolic [Ca2+] and [Na+] and a gradual intracellular acidification. The glyceraldehyde-induced rise in cytosolic [Na+] and intracellular acidification, but not the depolarization or rise in cytosolic [Ca2+], were reduced by dithiothreitol and 5-aminoguanidine, compounds which form chemical adducts with alpha-ketoaldehydes. Incubation of HIT cells with either D- or L-glyceraldehyde resulted in the formation of large amounts of D-lactate, the end product of methylglyoxal metabolism via the glyoxalase pathway. It is suggested that the depolarizing action of glyceraldehyde is the result, at least in part, of its electrogenic transport, probably via Na(+)-coupled entry into HIT cells involving an unidentified transport system. The intracellular acidification and a component of the increase in cytosolic [Na+] may be largely due to the presence of one or more dicarbonyl contaminants in the glyceraldehyde preparation.