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1 Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada
2 Department of Bioengineering, University of California, San Diego, San Diego, California, USA
* To whom correspondence should be addressed. E-mail: lomax{at}ucalgary.ca.
Consistent differences in the K+ currents in left and right atria of adult mouse hearts have been identified by applying current- and voltage-clamp protocols to isolated single myocytes. Left atrial myocytes had significantly (P < 0.05) larger peak outward K+ current density than did myocytes from the right atrium. Detailed analysis revealed that this difference was due to the rapidly activating sustained K+ current, which is inhibited by 100 µM 4-AP; this current was almost three times larger in left atrium than right atrium. Accordingly, 100 µM 4-AP caused a significantly (P < 0.05) larger increase in action potential duration in left than in right atrial myocytes. Inward rectifier K+ current density was also significantly (P < 0.05)larger in left atrial myocytes. There was no difference in ICa between left and right atria. As expected from this voltage-clamp data, the duration of action potentials recorded from single myocytes was significantly (P < 0.05) shorter in myocytes from left atria, and left atrial tissue was found to have a significantly (P < 0.05) shorter effective refractory period than right atrial tissue. These results reveal similarities between mice and other mammalian species where it is known that the left atrium repolarises more quickly than the right, and provide new insight into cellular electrophysiological mechanisms responsible for this difference. These findings, and previous results, suggest that the atria of adult mice may be a suitable model for detailed studies of atrial electrophysiology and pharmacology under control conditions and in the context of induced atrial rhythm disturbances.
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