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1 Department of Medical Physiology and Copenhagen Heart Research Center, The Panum Institute, Copenhagen, Denmark
2 Institute of Medical Anatomy, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
3 Institute of Biochemical Pharmacology, University of Innsbruck, Innsbruck, Austria
4 Division of Ion Channel Pharmacology, NeuroSearch A/S, Ballerup, Denmark
* To whom correspondence should be addressed. E-mail: hannebr{at}mfi.ku.dk.
In the heart several potassium channels are responsible for the repolarization of the cardiac action potential, these include transient outward and delayed rectifier potassium currents. In the present study the cellular and subcellular localization of the two delayed rectifier potassium channels KCNQ1 and ERG1 was investigated in the adult rat heart. Confocal immunofluorescence microscopy of atrial and ventricular cells revealed that while KCNQ1-labeling was detected in both the peripheral sarcolemma and a structure transversing the myocytes, ERG1-immunoreactivity was confined to the latter. Immunoelectron microscopy of atrial and ventricular myocytes showed that the ERG1 channel was primarily expressed in the transverse tubular system and its entrance, while KCNQ1 was detected in both the peripheral sarcolemma and in the T-tubules. Thus, while ERG1 displays a very restricted subcellular localization pattern, KCNQ1 is more widely distributed within the cardiac cells. The localization of these potassium channels to the transverse tubular system close to the Ca2+ channels renders them with maximal repolarizing effect.
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