© 2000 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Characterisation of the transient outward K+ current in rabbit sinoatrial node cells
aSchool of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
bResearch Institute of Environmental Medicine, Nagoya University, Nagoya 464-01, Japan
* Corresponding author. Tel.: +44-113-233-4298; fax: +44-113-233-4224 m.r.boyett{at}leeds.ac.uk
Objective: To (i) characterise the electrophysiological and pharmacological properties of the transient outward K+ current, Ito, (ii) determine the relationship between the density of Ito and cell size, and (iii) determine the role of Ito in electrical activity in rabbit sinoatrial node cells at 35°C. Methods: Rabbit sinoatrial node cells were studied using whole-cell voltage and current clamp techniques. Results: Ito showed half activation and inactivation at +11 and –49 mV, respectively. Ito was blocked by 4-aminopyridine (4-AP) as well as the class I agents, quinidine and flecainide, with EC50 values of 326, 21, and 19 µM, respectively. The densities of the transient and sustained components of 4-AP-sensitive current were significantly correlated with cell capacitance, a measure of cell size, and were greater in cells with a larger capacitance. Block of Ito by 4-AP affected both the action potential and pacemaker activity of sinoatrial node cells and the effects were greater in cells with a larger capacitance. Conclusions: Ito in sinoatrial node cells shows similar electrophysiological and pharmacological properties to Ito in atrial and ventricular cells. The expression of Ito in sinoatrial node cells is heterogeneous and differs in large and small cells (likely to be from the periphery and centre of the sinoatrial node, respectively). Ito plays an important role in action potential configuration and pacemaker activity in sinoatrial node cells, especially in larger cells.
KEYWORDS K+ channels; Sinus nodes
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