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This Article Full Text Full Text (PDF) Supplemental Figure All Versions of this Article: 295/1/R297    most recent 00612.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Hassinen, M. Articles by Vornanen, M. Search for Related Content PubMed PubMed Citation Articles by Hassinen, M. Articles by Vornanen, M.

COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Electrophysiological properties and expression of the delayed rectifier potassium (ERG) channels in the heart of thermally acclimated rainbow trout

Faculty of Biosciences, University of Joensuu, Joensuu, Finland

Submitted 23 August 2007 ; accepted in final form 29 April 2008

In ectotherms, compensatory changes in ion channel number and activity are needed to maintain proper cardiac function at variable temperatures. The rapid component of the delayed rectifier K⁺ current (I_Kr) is important for repolarization of cardiac action potential and, therefore, crucial for regulation of cellular excitability and heart rate. To examine temperature plasticity of cardiac I_Kr, we cloned the ether-à-go-go-related gene (ERG) channel and measured its electrophysiological properties in thermally acclimated rainbow trout (Oncorhynchus mykiss; omERG). The present findings demonstrate a complete thermal compensation in the whole cell conductance of the atrial I_Kr in rainbow trout acclimated to 4°C (cold acclimation) and 18°C (warm acclimation). In situ hybridization indicates that transcripts of the omERG channel are present throughout the muscular tissue of the heart, and quantitative PCR shows increased expression of the omERG in cold-acclimated trout compared with warm-acclimated trout. In both acclimation groups, omERG expression is higher in atrium than ventricle. In addition, the omERG has some functional features that support I_Kr activity at low temperatures. Voltage dependence of steady-state activation is completely resistant to temperature changes, and steady-state inactivation and activation kinetics are little affected by temperatures below 11°C. Collectively, these findings suggest that high density of cardiac I_Kr is achieved by cold-induced increase in the number of functional omERG channels and inherent insensitivity of the omERG to temperature below 11°C. These adaptations are probably important in maintaining high heart rates and proper excitability and contractility of trout cardiac myocytes in the cold.

fish heart; potassium current; temperature acclimation; cardiac action potential; excitation-contraction coupling