Nitric oxide‐dependent modulation of the delayed rectifier K + current and the L‐type Ca 2+ current by ginsenoside Re, an ingredient of Panax ginseng, in guinea‐pig cardiomyocytes

Ginsenoside Re, a major ingredient of Panax ginseng, protects the heart against ischemia–reperfusion injury by shortening action potential duration (APD) and thereby prohibiting influx of excessive Ca 2+ . Ginsenoside Re enhances the slowly activating component of the delayed rectifier K + current ( I Ks ) and suppresses the L‐type Ca 2+ current ( I Ca,L ), which may account for APD shortening. We used perforated configuration of patch‐clamp technique to define the mechanism of enhancement of I Ks and suppression of I Ca,L by ginsenoside Re in guinea‐pig ventricular myocytes.S ‐Methylisothiourea (SMT, 1 μ M ), an inhibitor of nitric oxide (NO) synthase (NOS), and N ‐acetyl‐ L ‐cystein (LNAC, 1 m M ), an NO scavenger, inhibited I Ks enhancement. Application of an NO donor, sodium nitroprusside (SNP, 1 m M ), enhanced I Ks with a magnitude similar to that by a maximum dose (20 μ M ) of ginseonside Re, and subsequent application of ginsenoside Re failed to enhance I Ks . Conversely, after I Ks had been enhanced by ginsenoside Re (20 μ M ), subsequently applied SNP failed to further enhance I Ks . An inhibitor of guanylate cyclase, 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ, 10 μ M ), barely suppressed I Ks enhancement, while a thiol‐alkylating reagent, N ‐ethylmaleimide (NEM, 0.5 m M ), clearly suppressed it. A reducing reagent, di‐thiothreitol (DTT, 5 m M ), reversed both ginsenoside Re‐ and SNP‐induced I Ks enhancement.I Ca,L suppression by ginsenoside Re (3 μ M ) was abolished by SMT (1 μ M ) or LNAC (1 m M ). NEM (0.5 m M ) did not suppress I Ca,L inhibition and DTT (5 m M ) did not reverse I Ca,L inhibition, whereas in the presence of ODQ (10 μ M ), ginsenoside Re (3 μ M ) failed to suppress I Ca,L . These results indicate that ginsenoside Re‐induced I Ks enhancement and I Ca,L suppression involve NO actions. Direct S ‐nitrosylation of channel protein appears to be the main mechanism for I Ks enhancement, while a cGMP‐dependent pathway is responsible for I Ca,L inhibition.British Journal of Pharmacology (2004) 142 , 567–575. doi: 10.1038/sj.bjp.0705814