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CARDIOVASCULAR

Mechanism of Myricetin Stimulation of Vascular L-type Ca²⁺ Current

Dipartimento di Scienze Biomediche, Università degli Studi di Siena, Siena, Italy

An in-depth analysis of the mechanism of the L-type Ca²⁺ current [I_Ca(L)] stimulation induced by myricetin was performed in rat tail artery myocytes using the whole-cell patch-clamp method. Myricetin increased I_Ca(L) in a frequency-, concentration-, and voltage-dependent manner. At holding potentials (V_h) 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, K_R, 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 I_Ca(L) or the T-type Ca²⁺ current. The Ca²⁺ channel blockers nifedipine, verapamil, and diltiazem antagonized I_Ca(L) in the presence of myricetin. Myricetin increased the time to peak of I_Ca(L) in a voltage- and concentration-dependent manner. Washout reverted myricetin effect on both current kinetics and amplitude at V_h of –90 mV while reverting only current kinetics at V_h of –50 mV. At the latter V_h, 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 V_h 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 (K_I) of 13.8 µM. Myricetin induced a frequency- and V_h-dependent block of I_Ca(L). In conclusion, myricetin behaves as an L-type Ca²⁺ channel agonist that stabilizes the channel in its inactivated state.

Address correspondence to: Dr. Fabio Fusi, Dipartimento di Scienze Biomediche, Università degli Studi di Siena, via A. Moro 2, 53100 Siena, Italy. E-mail: fusif{at}unisi.it