Genistein potentiates activity of the cation channel TRPC5 independently of tyrosine kinases.
OBJECTIVE
TRPC5 is a Ca(2+)-permeable channel with multiple modes of activation. We have explored the effects of genistein, a plant-derived isoflavone, on TRPC5 activity, and the mechanism(s) involved.


METHODS
Effects of genistein on TRPC5 channels were investigated in TRPC5-over-expressing human embryonic kidney 293 (HEK) cells and bovine aortic endothelial cells (BAECs) using fluorescent Ca(2+) imaging and electrophysiological techniques.


RESULTS
In TRPC5-over-expressing HEK cells, genistein stimulated TRPC5-mediated Ca(2+) influx, concentration dependently (EC(50)= 93 microM). Genistein and lanthanum activated TRPC5 channels synergistically. Effects of genistein on TRPC5 channels were mimicked by daidzein (100 microM), a genistein analogue inactive as a tyrosine kinase inhibitor, but not by known tyrosine kinase inhibitors herbimycin (2 microM), PP2 (20 microM) and lavendustin A (10 microM). Action of genistein on TRPC5 channels was not affected by an oestrogen receptor inhibitor ICI-182780 (50 microM) or a phospholipase C inhibitor U73122 (10 microM), suggesting genistein did not act through oestrogen receptors or phospholipase C. In BAECs, genistein (100 microM) stimulated TRPC5-mediated Ca(2+) influx. In patch clamp studies, both genistein (50 microM) and daidzein (50 microM) augmented TRPC5-mediated whole-cell cation current in TRPC5 over-expressing HEK cells. Genistein stimulated TRPC5 channel activity in excised inside-out membrane patch, suggesting that its action was relatively direct and did not require cytosolic factors.


CONCLUSIONS
The present study is the first to demonstrate stimulation of a TRP channel by isoflavones. Genistein is a lipophilic compound able to stimulate TRPC5 activity in TRPC5-over-expressing HEK cells and in native vascular endothelial cells.
Wong
Ching-On
CO
Li Ka Shing Institute of Health Sciences and School of Biomedical Sciences, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
Huang
Yu
Y
Yao
Xiaoqiang
X
D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D002460:Cell Line; D019833:Genistein / Q000494:pharmacology*; D006801:Humans; D018408:Patch-Clamp Techniques; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D050052:TRPC Cation Channels / Q000819:agonists*; D010738:Type C Phospholipases / Q000378:metabolism
D047428:Protein Kinase Inhibitors; D011960:Receptors, Estrogen; D050052:TRPC Cation Channels; C491780:TRPC5 protein, human; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases