Effects of (-)-epigallocatechin-3-gallate in Ca2+ -permeable non-selective cation channels and voltage-operated Ca2+ channels in vascular smooth muscle cells.
The effects of (-)-epigallocatechin-3-gallate (EGCG), the most abundant catechin of tea, on Ca(2+)-permeable non-selective cation currents (NSCC) and voltage-operated Ca(2+) channels (VOCC) have been investigated in cultured rat aortic smooth muscle cells using the whole-cell voltage-clamp technique. Under the Cs(+)/tetraethylammonium (TEA)-containing internal solution, and in the presence of nifedipine (1 microM), EGCG (30 microM) activated a long-lasting inward current, with a reversal potential (E(rev)) of approximately 0 mV. This current was not significantly altered by the replacement of [Cl(-)](i) or [Cl(-)](o), implying that the inward current was not a chloride channel, but a NSCC. SKF 96365 (30 microM) and Cd(2+) (500 microM) almost completely abolished the EGCG-induced NSCC. A higher dose of EGCG (100 microM) additionally activated a nifedipine-sensitive inward current in the absence of depolarization protocol. EGCG (100 microM) also potentiated a nifedipine-sensitive voltage-dependent Ba(2+)-current during the first 5 min of incubation. However, after > 10 min of incubation with EGCG, this current was significantly inhibited. Our results suggest that EGCG caused a Ca(2+) influx into smooth muscle cells via VOCC (probably L-type) and other SKF-96365- and Cd(2+)-sensitive Ca(2+)-permeable channels. The action described here may be responsible for the contraction induced by EGCG in rat aortic rings and for the rise of the intracellular concentration of Ca(2+) in rat aortic smooth muscle cells evoked by this catechin. On the other hand, the inhibition of VOCC after > 10 min of incubation may be, in part, responsible for the relaxation of rat aorta induced by EGCG.
Campos-Toimil
Manuel
M
Departamento de Farmacoloxía, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Universitario Sur, E-15782 Santiago de Compostela (A Coruña), Spain.
Orallo
Francisco
F
Departamento de Farmacoloxía, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Universitario Sur, E-15782 Santiago de Compostela (A Coruña), Spain. Electronic address: fforallo@usc.es.
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D002412:Cations / Q000737:chemistry*; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032383:Myocytes, Cardiac / Q000166:cytology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D000975:Antioxidants; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002412:Cations; D007093:Imidazoles; D002392:Catechin; C045651:epigallocatechin gallate; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium