Genistein potentiates activity of the cation channel TRPC5 independently of tyrosine kinases

Background and purpose:

TRPC5 is a Ca²⁺-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.

Experimental approach:

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 Ca²⁺ imaging and electrophysiological techniques.

Key results:

In TRPC5-over-expressing HEK cells, genistein stimulated TRPC5-mediated Ca²⁺ influx, concentration dependently (EC₅₀= 93 µM). Genistein and lanthanum activated TRPC5 channels synergistically. Effects of genistein on TRPC5 channels were mimicked by daidzein (100 µM), a genistein analogue inactive as a tyrosine kinase inhibitor, but not by known tyrosine kinase inhibitors herbimycin (2 µM), PP2 (20 µM) and lavendustin A (10 µM). Action of genistein on TRPC5 channels was not affected by an oestrogen receptor inhibitor ICI-182780 (50 µM) or a phospholipase C inhibitor {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122 (10 µM), suggesting genistein did not act through oestrogen receptors or phospholipase C. In BAECs, genistein (100 µM) stimulated TRPC5-mediated Ca²⁺ influx. In patch clamp studies, both genistein (50 µM) and daidzein (50 µM) 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 and implications:

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.