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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Cloning and expression of cardiac K_ir2.1 and K_ir2.2 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_ir2.2 transcripts were expressed in atrium and ventricle of the trout heart, K_ir2.1 being the major component in both cardiac chambers. The relative expression of K_ir2.2 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 Ba²⁺ (IC₅₀ 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_ir2 channels was slower in WA than CA trout (P < 0.05). When expressed in COS-1 cells, the homomeric K_ir2.2 channels demonstrated higher Ba²⁺ sensitivity (2.88 ± 0.42 µM) than K_ir2.1 channels (24.99 ± 7.40 µM) (P < 0.05). In light of the different Ba²⁺ sensitivities of rainbow trout (om)K_ir2.1 and omK_ir2.2 channels, it is concluded that warm acclimation increases either number or activity of the omK_ir2.2 channels in trout ventricular myocytes. The functional changes in I_K1 are independent of omK_ir2 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_ir2 channels, which may be needed for regulation of cardiac excitability at variable temperatures.

inward rectifier potassium channels; atrial myocytes; ventricular myocytes; thermal plasticity

This article has been cited by other articles:

				M. Hassinen, J. Haverinen, and M. Vornanen Electrophysiological properties and expression of the delayed rectifier potassium (ERG) channels in the heart of thermally acclimated rainbow trout Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2008; 295(1): R297 - R308. [Abstract] [Full Text] [PDF]