摘要：Many lines of evidences have shown that Panax ginseng exhibits beneficial effects on cardiovascular systems. We previously demonstrated that ginsenoside Rg3 (Rg3), one of active ingredients of Panax ginseng , inhibits Ca2+ channel currents in a stereospecific manner and affects the steady-state activation but not inactivation. This points a possibility that Rg3 regulates Ca2+ channels through specific interaction site(s) for Ca2+ influx inhibition through Ca2+ channels. However, it was not known how Rg3 interacts with Ca2+ channel proteins. In the current study, we sought to identify these site(s) in Xenopus oocytes expressing cardiac wild-type and mutant L(α1C)-type Ca2+ channels using the two-microelectrode voltage-clamp technique. To this end, we assessed how various point mutations of the L-type Ca2+ channel affected the Rg3 action. Mutations of L427R, N428R and L431K in transmembrane domain-I-segment 6 (IS6) of the channel significantly attenuated the Rg3 action and caused rightward shifts in dose–response curves. Rg3 treatment produced a negative shift in the inactivation voltage but did not alter the steady-state activation voltage, and none of the mutant channels affected the Rg3-induced negative shift of inactivation voltage. Rg3 had no effects on inactivation time constant in wild-type and mutant channels. These results indicate that Rg3 inhibition of L-type Ca2+ channel currents is attenuated by mutations of Leu427, Asn428 and Leu431 in transmembrane IS6 residues. Leu427, Asn428 and Leu431 residues of the L-type Ca2+ channel play important roles in the Rg3 effect on channel properties.
