Abstract
An in-depth analysis of the mechanism of the L-type Ca2+ current [ICa(L)] stimulation induced by myricetin was performed in rat tail artery myocytes using the whole-cell patch-clamp method. Myricetin increased ICa(L) in a frequency-, concentration-, and voltage-dependent manner. At holding potentials (Vh) of –50 and –90 mV, the pEC50 values were 4.9 ± 0.1 and 4.2 ± 0.1, respectively; the latter corresponded to the drug-apparent dissociation constant for resting channels, KR, of 67.6 μM. Myricetin shifted the maximum of the current-voltage relationship by 10 mV in the hyperpolarizing direction but did not modify the threshold for ICa(L) or the T-type Ca2+ current. The Ca2+ channel blockers nifedipine, verapamil, and diltiazem antagonized ICa(L) in the presence of myricetin. Myricetin increased the time to peak of ICa(L) in a voltage- and concentration-dependent manner. Washout reverted myricetin effect on both current kinetics and amplitude at Vh of –90 mV while reverting only current kinetics at Vh of –50 mV. At the latter Vh, myricetin shifted the voltage dependence of inactivation and activation curves to more negative potentials by 6.4 and 13.0 mV, respectively, in the mid-potential of the curves. At Vh of –90 mV, myricetin shifted, in a concentration-dependent manner, the voltage dependence of the inactivation curve to more negative potentials with an apparent dissociation constant for inactivated channels (KI) of 13.8 μM. Myricetin induced a frequency- and Vh-dependent block of ICa(L). In conclusion, myricetin behaves as an L-type Ca2+ channel agonist that stabilizes the channel in its inactivated state.
Footnotes
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This work was supported by grants from the Università degli Studi di Siena (PAR 2002 and 2001 Young Researcher to S.S.) and a grant from the Tuscany Region (Carabiotech 2002).
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doi:10.1124/jpet.104.080135.
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ABBREVIATIONS: PSS, physiological salt solution; Bay K 8644, (S)-(–)-methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate.
- Received November 4, 2004.
- Accepted January 20, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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