Published online Jan 21, 2006. doi: 10.3748/wjg.v12.i3.420
Revised: June 28, 2005
Accepted: July 15, 2005
Published online: January 21, 2006
AIM: 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 µmol/L) reversibly and dose-dependently reduced the peak amplitude of IKto with an IC50 value of 22.0±6.9 µmol/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).
CONCLUSION: GST can dose-dependently and reversibly block voltage-gated potassium channels in guinea pig proximal colon smooth muscle cells.