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Evidence-Based Complementary and Alternative Medicine
Volume 1 (2004), Issue 3, Pages 277-284
http://dx.doi.org/10.1093/ecam/neh044
Original Article

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

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

Received 27 July 2004; Accepted 16 September 2004

Copyright © 2004 Hiroyasu Satoh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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 0.1–3μM 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.