External K+ increases Na+ conductance of the hyperpolarization-activated current in rabbit cardiac pacemaker cells.
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.
Frace
A M
AM
Department of Physiology, Faculty of Medicine Kyushu University, Fukuoka, Japan.
Maruoka
F
F
Noma
A
A
D000818:Animals; D001683:Biological Clocks / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D011817:Rabbits; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects*
D015222:Sodium Channels; D011188:Potassium