A CHLOROFORM EXTRACT OF THE HERB FEVERFEW BLOCKS VOLTAGE-DEPENDENT POTASSIUM CURRENTS RECORDED FROM SINGLE SMOOTH-MUSCLE CELLS

We have studied the effects of a chloroform extract of fresh leaves fr om the herb feverfew (Tanacetum parthenium) on potassium currents in s mooth muscle. The currents were recorded from single cells dissociated from the rat anococcygeus and the rabbit ear artery using the whole-c ell patch-clamp technique. When applied to cells isolated from the rat anococcygeus, the extract reduced the inactivating voltage-dependent potassium current in a concentration-related manner, with an IC50 valu e (the concentration that reduced the current by 50%) of 56 mug mL-1. Complete block of the current occurred at 1 mg mL-1. In addition to re ducing the peak current, feverfew decreased the time to peak of the cu rrent and increased the rate of decay of the current. These effects ca n be explained by the feverfew extract blocking open potassium channel s. In single cells isolated from rabbit ear artery the feverfew extrac t again reduced the voltage-dependent potassium current, whilst at the same time having no effect on the spontaneous transient outward curre nts which arise as a consequence of activation of calcium-dependent po tassium channels. These results suggest that chloroform extracts of fe verfew leaf contain an as yet unidentified substance capable of produc ing a selective, open-channel block of voltage-dependent potassium cha nnels.