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

Abstract

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 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.