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Keimyung Medical Journal 1996;15(3):231-236.
Effects of External Divalent Cations on Delayed Rectifier K+ Current in Rabbit Sinoatrial Node Cells
토끼 동방결절 세포의 Delayed Rectifier K+ 전류에 미치는 이가 양이온의 차단효과
송대규; 호원경; 엄융의
Abstract
In sinoatrial(SA) node cells; K+ conductance increases only when the membrane is depolarized and the delayed rectifier K+ current; it; is activated. This leads to repolarization which in turn induces the deactivation of ik channel; causing the membrane potential to depolarize once again towards the threshold of the action potential. Therefore the decay of ik plays a key role in the pacemaker depolarization. In the present study; we have investigated the effects of divalent cations(Niz+; Ba2+; Coz+; and Mn2+) on the delayed rectifier K+ current in rabbit SA node cells using the whole cell voltage clamp technique. CsCl(2 mM) was added to block the hyperpolarization activated inward current(if). K+ currents were record?ed in high K+(140 mM) solution. When divalent cations were added to a control solution; they reduced both the instantaneous and the steady -state values of currents recorded on hyperpolarization. The blockade was potential-dependent; and steady- state currents were significantly reduced with increasing hyperpolarization. The inward currents that recorded during hyperpolarizing voltage steps were relaxed exponentially with time as the blockade by divalent cations developed. Increased the concentration of the divalent cations elevated the rate of the blockade at a given potential. These phenomena were highly sensitive to temperature; suggesting the presence of ionic binding sit?es on the channel. Inward K+ currents measured at -80 mV after various depolarizing prepulses(-10 to -40 mV) were increased in the more depolarizing prepulses; and showed the steady-state blocking evidence at 0.1 mM Ni2+. Ni2+; Ba2+; Co2+; and Mn2+ had a similar effect; but the velocity of the blocking action is slightly different from one another(Ni2+ > Co2+ > Mn2+ > Ba2+).
Key Words: sinoatrial node cell, delayed rectifier K+ channel, divalent cations
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