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eCAM Advance Access published online on October 27, 2004
eCAM, doi:10.1093/ecam/neh044
Copyright © 2004 by the Oxford University Press.
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Received July 27, 2004
Accepted September 16, 2004

Original Article

Comparative Electropharmacological Actions of Some Constituents from Ginkgo biloba Extract in Guinea-pig Ventricular Cardiomyocytes

Hiroyasu Satoh 1*

1 Department of Pharmacology, Division of Molecular and Cellular Biology, Nara Medical University, School of Medicine, Japan

* To whom correspondence should be addressed.
Hiroyasu Satoh, E-mail: hysat{at}naramed-u.ac.jp


  Abstract

Effects of the constituents from Ginkgo biloba extract (GBE) on the action potentials and the ionic currents in guinea pig ventricular cardiomyocytes were investigated using whole-cell and current-clamp techniques. The constituents, ginkgolides A, B, C and quercetin, had depressant effects at 0.1-3 µM on the action potential configuration. Ginkgolide A (1-3 µM) prolonged the action potential (action potential duration: APD) at 75% and 90% repolarizations (APD75 and APD90). However, ginkgolides B and C at low concentrations prolonged APD, but at higher concentrations (>1 µM) shortened APD. Quercetin at 3 µM prolonged the APD, but not at the lower concentrations. These constituents also inhibited the Vmax. The resting potential was unaffected. In voltage-clamp experiments, ginkgolides A and B (0.1-3 µM) markedly and concentration-dependently increased the Ca2+ current (ICa) and the delayed rectifier K+ current (IK), and decreased the inwardly rectifying K+ current (IK1). On the other hand, ginkgolide C failed to affect the ICa but increased the IK by 14.0 ± 2.3% (n = 6, P < 0.05) at 1 µM. Quercetin inhibited ICa, and enhanced IK but decreased IK1. These responses to the constituents were almost reversible (80-90% of control) after a 10- to 20-min washout. These results indicate that even at acute administrations, these constituents produce the effective actions on the APD and the underlying ionic currents in cardiomyocytes. Each constituent does not exhibit a uniform response, although GBE acts as a net.

Keywords: action potential; ionic currents; ginkgolide A; ginkgolide B; ginkgolide C; Ginkgo biloba extract; guinea pig ventricular cardiomyocytes; quercetin.
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