Nitric oxide-dependent modulation of the delayed rectifier K+ current and the L-type Ca2+ current by ginsenoside Re, an ingredient of Panax ginseng, in guinea-pig cardiomyocytes

1 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 Ca2+. Ginsenoside Re enhances the slowly activating component of the delayed rectifier K+ current (I-Ks,) and suppresses the L-type Ca2+ current (I-Ca,I-I.), which may account for APD shortening. 2 We used perforated configuration of patch-clamp technique to define the mechanism of enhancement of I-Ks and suppression of I-Ca,I-L by ginsenoside Re in guinea-pig ventricular myocytes. 3 S-Methylisothiourea (SMT, 1 mum), an inhibitor of nitric oxide (NO) synthase (NOS), and N-acetyl-L-cystein (LNAC, 1 mm), an NO scavenger, inhibited I-Ks enhancement. Application of an NO donor, sodium nitroprusside (SNP, 1 mm), enhanced I-Ks with a magnitude similar to that by a maximum dose (20 mum) 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 mum), subsequently applied SNP failed to further enhance I-Ks. 4 An inhibitor of guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 mum), barely suppressed I-Ks enhancement, while a thiol-alkylating reagent, N-ethylmaleimide (NEM, 0.5 mm). clearly suppressed it. A reducing reagent, di-thiothreitol (DTT, 5 mm), reversed both ginsenoside Re- and SNP-induced I-Ks enhancement. 5 I-Ca.L suppression by ginsenoside Re (3 mum) was abolished by SMT (1 mum) or LNAC (1 mm). NEM (0.5 mm) did not suppress I-Ca,I-L inhibition and DTT (5 mm) did not reverse I-Ca,I-L inhibition, whereas in the presence of ODQ (10 mum), ginsenoside Re (3 mum) failed to suppress I-C,I-La. 6 These results indicate that ginsenoside Re-induced I-Ks enhancement and I-Ca,I-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,I-L inhibition.