Frace A M, Maruoka F, Noma A
Department of Physiology, Faculty of Medicine Kyushu University, Fukuoka, Japan.
Pflugers Arch. 1992 Jun;421(2-3):97-9.
The hyperpolarization-activated current (I(f)) was recorded from single myocytes dissociated from rabbit sinoatrial node. Although I(f) is usually carried by both Na+ and K+, removal of the minor K+ component from physiological saline suppresses inward component. This inward Na+ current through I(f) channel increases on raising the extracellular K+ concentration. The Na+ conductance relative to K+ conductance (PNa/PK), as measured from the reversal potential, increases and saturates near 5 mM K+. This effect is different from the current increase caused by raising the concentration of carrier ion K+, which saturates at 70 mM with a half-maximal value (K1/2) of 10 mM. It is suggested that the I(f) channel has multiple, interactive binding sites for cation permeation.
从兔窦房结分离的单个心肌细胞记录超极化激活电流（I(f)）。虽然I(f)通常由Na+和K+共同携带，但从生理盐水中去除少量K+成分会抑制内向成分。通过I(f)通道的这种内向Na+电流会随着细胞外K+浓度升高而增加。从反转电位测量的相对于K+电导的Na+电导（PNa/PK）在接近5 mM K+时增加并达到饱和。这种效应不同于因载体离子K+浓度升高引起的电流增加，后者在70 mM时达到饱和，半最大值（K1/2）为10 mM。提示I(f)通道具有多个用于阳离子通透的相互作用结合位点。
