Effect of genistein on voltage-gated potassium channels in guinea pig proximal colon smooth muscle cells.
OBJECTIVE
To investigate the action of genistein (GST), a broad spectrum tyrosine kinase inhibitor, on voltage-gated potassium channels in guinea pig proximal colon smooth muscle cells.


METHODS
Smooth muscle cells in guinea pig proximal colon were enzymatically isolated. Nystatin-perforated whole cell patch clamp technique was used to record potassium currents including fast transient outward current (IKto) and delayed rectifier current (IKdr), two of which were isolated pharmacologically with 10 mmol/L tetraethylammonium or 5 mmol/L 4-aminopyridine. Contamination of calcium-dependent potassium currents was minimized with no calcium and 0.2 mmol/L CdCl2 in an external solution.


RESULTS
GST (10-100 micromol/L) reversibly and dose-dependently reduced the peak amplitude of IKto with an IC50 value of 22.0+/-6.9 micromol/L. To a lesser extent, IKdr was also inhibited in both peak current and sustained current. GST could not totally block the outward potassium current as a fraction of the outward potassium current, which was insensitive to GST. GST had no effect on the steady-state activation (n=6) and inactivation kinetics (n=6) of IKto. Sodium orthovanadate (1 mmol/L), a potent inhibitor of tyrosine phosphatase, significantly inhibited GST-induced inhibition (P<0.05).


CONCLUSIONS
GST can dose-dependently and reversibly block voltage-gated potassium channels in guinea pig proximal colon smooth muscle cells.
Xiamen Institute of Medicine, 2 Tongan Road, Xiamen 361003, Fujian Province, China. shiyingli@21cn.com
Shi-Ying
SY
Li
Bin-Bin
BB
Huang
Shou
S
Ouyang
D000818:Animals; D003106:Colon / Q000166:cytology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D019833:Genistein / Q000378:metabolism / Q000494:pharmacology*; D006168:Guinea Pigs; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D014638:Vanadates / Q000378:metabolism
D004791:Enzyme Inhibitors; D024642:Potassium Channels, Voltage-Gated; D014638:Vanadates; D019833:Genistein