Mechanism of myricetin stimulation of vascular L-type Ca2+ current.
An in-depth analysis of the mechanism of the L-type Ca(2+) 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 pEC(50) 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 microM. 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 Ca(2+) current. The Ca(2+) 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 muM. Myricetin induced a frequency- and V(h)-dependent block of I(Ca(L)). In conclusion, myricetin behaves as an L-type Ca(2+) channel agonist that stabilizes the channel in its inactivated state.
Fusi
Fabio
F
Dipartimento di Scienze Biomediche, Università degli Studi di Siena, Italy. fusif@unisi.it
Sgaragli
Giampietro
G
Saponara
Simona
S
D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids / Q000494:pharmacology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013623:Tail / Q000098:blood supply
D020746:Calcium Channels, L-Type; D005419:Flavonoids; C040015:myricetin