Blocking effects of extracellular Cd~(2+) on the inward rectifier potassium channel / 中国病理生理杂志

ABSTRACT

AIM: To study the blocking effects of extracellular Cd 2+ on the inward rectifier potassium channel (IRK1) expressed in the Xenopus oocytes METHODS:Two-microelectrode voltage clamp (TEV) method was used RESULTS:Cd 2+ can concentration-, time- and voltage dependently block IRK1 instantaneous currents ( 1 5 ms after voltage applied ) when external Cd 2+ 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 Cd 2+ almost has no effect on the gating property and outward currents of IRK1 Cd 2+ can concentration-dependently increase the normalized conductance of IRK1 IRK1 can not permeate Cd 2+ because reverse potential did not change Three exponential fitting analyze indicates that time constant is not changed with the change in Cd 2+ concentration This shows that the inhibitory effects of Cd 2+ may be caused by surface potential or the blocking site of Cd 2+ is at the surface of the channel Because external Cd 2+ can not inhibit IRK1 macroscopic currents more powerfully when external Cd 2+ concentration is lower These mean that external Cd 2+ does not work through surface potential mechanism CONCLUSION: Cd 2+ is considered as one of the fast open channel blockers of IRK1 and its blocking site is at the surface of the channel