Vasodilators are used clinically for the treatment of hypertension and heart failure. The effects of some vasodilators seem to be mediated by membrane hyperpolarization. The molecular basis of this hyperpolarization has been investigated by examining the properties of single K ⁺ channels in arterial smooth muscle cells. The presence of adenosine triphosphate (ATP)-sensitive K ⁺ channels in these cells was demonstrated at the single channel level. These channels were opened by the hyperpolarizing vasodilator cromakalim and inhibited by the ATP-sensitive K ⁺ channel blocker glibenclamide. Furthermore, in arterial rings the vasorelaxing actions of the drugs diazoxide, cromakalim, and pinacidil and the hyperpolarizing actions of vasoactive intestinal polypeptide and acetylcholine were blocked by inhibitors of the ATP-sensitive K ⁺ channel, suggesting that all these agents may act through a common pathway in smooth muscle by opening ATP-sensitive K ⁺ channels.

Green tea catechins, including (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG), are oxidized and dimerized during the manufacture of black tea and oolong tea to form orange-red pigments, theaflavins (TF), a mixture of theaflavin (TF₁), theaflavin-3-gallate (TF₂A), theaflavin-3′-gallate (TF₂B) and theaflavin-3,3′-digallate (TF₃). The present study was designed to compare the antioxidant activities of individual TF with that of each catechin using human LDL oxidation as a model. All catechins and TF tested inhibited Cu⁺²-mediated LDL oxidation. Analysis of the thiobarbituric acid–reactive substances (TBARS) and conjugated dienes produced during LDL oxidation revealed that the antioxidant activity was in the order: TF₃ > ECG > EGCG ≥ TF₂B ≥ TF₂A > TF₁ ≥ EC > EGC. Four TF derivatives also demonstrated a dose-dependent antioxidant activity in Cu⁺²-mediated LDL oxidation at concentrations of 5–40 μmol/L. These results demonstrate that the TF present in black tea possess at least the same antioxidant potency as catechins present in green tea, and that the conversion of catechins to TF during fermentation in making black tea does not alter significantly their free radical–scavenging activity.