Blocking effects of extracellular Cd2+ on the inward rectifier potassium channel / 中国病理生理杂志

ABSTRACT

AIM:To study the blocking effects of extracellular Cd2+ on the inward rectifier potassium channel (IRK1) expressed in the Xenopus oocytes. METHODS：Two-microelectrode voltage clamp (TEV) method was used. RESULTS：Cd2+ can concentration-, time- and voltage dependently block IRK1 instantaneous currents ( 1.5 ms after voltage applied ) when external Cd2+ concentration is 0, 0.1, 0.15, 0.3, 0.9, 2.7 or 5.4 mmol/L with K+ concentration fixed to 90 mmol/L. Cd2+ almost has no effect on the gating property and outward currents of IRK1. Cd2+ can concentration-dependently increase the normalized conductance of IRK1. IRK1 can not permeate Cd2+ because reverse potential did not change. Three exponential fitting analyze indicates that time constant is not changed with the change in Cd2+ concentration. This shows that the inhibitory effects of Cd2+ may be caused by surface potential or the blocking site of Cd2+ is at the surface of the channel. Because external Cd2+ can not inhibit IRK1 macroscopic currents more powerfully when external Cd2+ concentration is lower. These mean that external Cd2+ does not work through surface potential mechanism.CONCLUSION:Cd2+ is considered as one of the fast open channel blockers of IRK1 and its blocking site is at the surface of the channel.