Cloning and expression of cardiac Kir2.1 and Kir2.2 channels in thermally acclimated rainbow trout

Department of Biology, University of Joensuu, Joensuu, Finland Submitted 26 May 2006 ; accepted in final form 31 January 2007 Potassium currents are plastic entities that modify electrical activity of the heart in various physiological conditions including chronic thermal stress. We examined the molecular basis of the inward rectifier K + current ( I K1 ) in rainbow trout acclimated to cold (4°C, CA) and warm (18°C, WA) temperature. Inward rectifier K + channel (K ir )2.1 and K ir 2.2 transcripts were expressed in atrium and ventricle of the trout heart, K ir 2.1 being the major component in both cardiac chambers. The relative expression of K ir 2.2 was, however, higher ( P < 0.05) in atrium than ventricle. The density of ventricular I K1 was 25% larger ( P < 0.05) in WA than CA trout. Furthermore, the I K1 of the WA trout was 10 times more sensitive to Ba 2+ (IC 50 0.18 ± 0.42 µM) than the I K1 of the CA trout (1.17 ± 0.44 µM) ( P < 0.05), and opening kinetics of single K ir 2 channels was slower in WA than CA trout ( P < 0.05). When expressed in COS-1 cells, the homomeric K ir 2.2 channels demonstrated higher Ba 2+ sensitivity (2.88 ± 0.42 µM) than K ir 2.1 channels (24.99 ± 7.40 µM) ( P < 0.05). In light of the different Ba 2+ sensitivities of rainbow trout (om)K ir 2.1 and omK ir 2.2 channels, it is concluded that warm acclimation increases either number or activity of the omK ir 2.2 channels in trout ventricular myocytes. The functional changes in I K1 are independent of omK ir 2 transcript levels, which remained unaltered by thermal acclimation. Collectively, these findings suggest that thermal acclimation modifies functional properties and subunit composition of the trout K ir 2 channels, which may be needed for regulation of cardiac excitability at variable temperatures. inward rectifier potassium channels; atrial myocytes; ventricular myocytes; thermal plasticity Address for reprint requests and other correspondence: M. Vornanen, Dept. of Biology, Univ. of Joensuu, PO Box 111, 80101 Joensuu, Finland (e-mail: matti.vornanen{at}joensuu.fi )