Mutations Leu427, Asn428, and Leu431 Residues within Transmembrane Domain-I-Segment 6 Attenuate Ginsenoside-Mediated L-Type Ca2+ Channel Current Inhibitions

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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.
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Mutations Leu427, Asn428, and Leu431 Residues within Transmembrane Domain-I-Segment 6 Attenuate Ginsenoside-Mediated L-Type Ca2+ Channel Current Inhibitions

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