Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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We examined ascorbate transport in pig coronary artery rings and in smooth muscle cells cultured from them. The cultured cells accumulated ascorbate from the medium in the presence of Na+. The anion transport inhibitors DIDS (4,4-Diisothiocyanatostilbene-2,2-disulfonate) and sulfinpyrazone inhibited ascorbate uptake but the glucose transport inhibitor cytochalasin B did not. The accumulated material was determined to be ascorbate using HPLC. The ascorbate accumulation data fitted best with a Hill-coefficient of 1 for ascorbate (Kasc = 26 ± 5 µM ) and 2 for Na+ (KNa= 94 ± 16 mM) suggesting a stoichiometry of 2 Na+: 1 ascorbate, hence an electrogenic transport. Consistent with this electrogenic nature, membrane depolarization inhibited the ascorbate accumulation. De-endothelialized artery rings also accumulated ascorbate. This accumulation was Na+-dependent and inhibited by sulfinpyrazone. Adding ascorbate to the arteries in a Na+-containing solution depolarized the membranes by 4-5 mV confirming the electrogenic nature of the transporter. These properties of the ascorbate transporter allow smooth muscle cells to sequester ascorbate. Transferring cultured cells loaded with 14C-ascorbate into an ascorbate free solution resulted in a biphasic loss of radioactivity - an initial faster phase lasting several min and a subsequent slower phase. Sulfinpyrazone and DIDS inhibited the slower efflux phase more than the faster phase. ATP, angiotensin II, histamine, serotonin, endothelin-1, carbachol, A23187 or SIN1 did not affect the efflux. Including peroxide or superoxide in the efflux solution increased the loss of ascorbate. We conclude that coronary artery smooth muscle accumulates ascorbate using an electrogenic Na+-ascorbate symporter and that the accumulated ascorbate may be used by the tissue during oxidative stress encountered during ischemia-reperfusion.

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Poster Number PAholmes0113
Keywords: Vitamin C, transport, oxidative stress, ischemia, reperfusion