Quercetin as a novel activator of L-type Ca[sup2+] channels in rat tail artery smooth muscle cells.

1 The aim of this study was to investigate the effects of quereetin, a natural polyphenolic flavonoid, on voltage-dependent Ca[sup2+] channels of smooth muscle cells freshly isolated from the rat tail artery, using either the conventional or the amphotericin B-perforated whole-cell patch-clamp method. 2 Quercetin increased L-type Ca[sup2] current[I[sub Ca(L)] in a concentration- (pEC[sub50]= 5.09±0.05) and voltage-dependent manner and shifted the maximum of the current-voltage relationship by 10 mV in the hyperpolarizing direction, without, however, modifying the threshold and the equilibrium potential for Ca[sup2+], Quercetin-indueed I[subCa(L)] stimulation was reversible upon wash-out. T-type Ca[sup2] current was not affected by quercetin. 3 Quercetin shifted the voltage dependence of the steady-state inactivation and activation curves to more negative potentials by about 5.5 and 7.5 mV respectively, in the mid-potential of the curves as well as increasing the slope of activation. Quercetin slowed both the activation and the deactivation kinetics of the I[subCa(L)]. The inactivation time course was also slowed but only at voltages higher than 10 mV. Moreover quercetin slowed the rate of recovery from inactivation. 4 These results prove quercetin to be a naturally-occurring L-type Ca[sup2] channel activator. [ABSTRACT FROM AUTHOR]