Ascorbate transport in pig coronary artery smooth muscle: Na+ removal and oxidative stress increase loss of accumulated cellular ascorbate

Pig deendothelialized coronary artery rings and smooth muscle cells culture d from them accumulated ascorbate from medium containing Na+. The accumulat ed material was determined to be ascorbate using high-performance liquid ch romatography, We further characterized ascorbate uptake in the cultured cel ls. The data fitted best with a Hill coefficient of 1 for ascorbate (K-asc = 22 +/- 2 mu M) and 2 for Na+ (K-Na = 84 +/- 10 mM), The anion transport i nhibitors sulfinpyrazone and 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS) inhibited the uptake. Transferring cultured cells loaded with C-14- ascorbate into an ascorbate-free solution resulted in a biphasic loss of ra dioactivity - an initial sulfinpyrazone-insensitive faster phase and a late sulfinpyrazone-sensitive slower phase. Transferring loaded cells into a Na +-free medium increased the loss in the initial phase in a sulfinpyrazone-s ensitive manner, suggesting that the ascorbate transporter is bidirectional . Including peroxide or superoxide in the solution increased the loss of ra dioactivity. Thus, ascorbate accumulated in coronary artery smooth muscle c ells by a Na+-dependent transporter was lost in an ascorbate-free solution, and the loss was increased by removing Na+ from the medium or by oxidative stress. Copyright (C) 2000 S. Karger AG, Basel.