AI Article Synopsis
- The hyperpolarization-activated current (I(f)) in rabbit sinoatrial node myocytes is primarily carried by sodium (Na+) ions when the potassium (K+) contribution is minimized.
- Increasing extracellular K+ concentration enhances Na+ current through I(f) channels, with the Na+ to K+ conductance ratio peaking around 5 mM K+.
- The I(f) channel likely features multiple interactive binding sites for different cations, contributing to its unique response to changes in ion concentration.
Article Abstract
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.
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