Electrophysiological effects of phytoestrogen genistein on pacemaker cells in sinoatrial nodes of rabbits

摘要

AIM: To study the electrophysiological effects of genistein (GST) on pacemaker cells in sinoatrial (SA) nodes of rabbits. METHODS: Parameters of action potential (AP) in SA node were recorded using intracellular microelectrode technique. RESULTS: GST (10 - 150μmol/L) not only decreased the amplitude of action potential (APA), maximal rate of depolarization (V_(max)) [from (6.2 +- 2.8) to (2.8 +- 1.4) V/s, P < 0.01], velocity of diastolic (phase 4) depolarization (VDD) [from (55 +- 14) to (38 +- 8) mV/ s, P < 0.01], and rate of pacemaker firing (RPF) [from (154 +- 23) to (107 +- 25) beat/min, P < 0.01], but also prolonged duration of 90 % repolarization of action potential (APD_(90)) in a concentration-dependent manner. Both elevation of calcium concentration (5 mmol/L) in superfusate and application of L-type Ca~(2+) channel agonist Bay K8644 (0.5μmol/L) reversed the inhibitory effects of GST on pacemaker cells, while pretreatment with N~G-nitro-L-arginine methyl ester ( L-NAME, 1 mmol/L), an NO synthase inhibitor, failed to block the electrophysiological effects of GST. CONCLUSION: GST exerted a negative chronotropic action and induced a delayed repolarization of pacemaker cells in SA nodes of rabbits. These effects were likely due to reduction in calcium influx and potassium efflux, but had no association with NO release.