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This Article Full Text Full Text (PDF) All Versions of this Article: 297/2/R502    most recent 90810.2008v1 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 Google Scholar Articles by Galli, G. L. J. Articles by Block, B. A. PubMed PubMed Citation Articles by Galli, G. L. J. Articles by Block, B. A.

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Effect of thermal acclimation on action potentials and sarcolemmal K⁺ channels from Pacific bluefin tuna cardiomyocytes

Stanford University, Palo Alto, California; and Hopkins Marine Station of Stanford University, Monterey, California

Submitted 5 October 2008 ; accepted in final form 10 June 2009

To sustain cardiac muscle contractility relatively independent of temperature, some fish species are capable of temporarily altering excitation-contraction coupling processes to meet the demands of their environment. The Pacific bluefin tuna, Thunnus orientalis, is a partially endothermic fish that inhabits a wide range of thermal niches. The present study examined the effects of temperature and thermal acclimation on sarcolemmal K⁺ currents and their role in action potential (AP) generation in bluefin tuna cardiomyocytes. Atrial and ventricular myocytes were enzymatically isolated from cold (14°C)- and warm (24°C)-acclimated bluefin tuna. APs and current-voltage relations of K⁺ channels were measured using the whole cell current and voltage clamp techniques, respectively. Data were collected either at the cardiomyocytes' respective acclimation temperature of 14 or 24°C or at a common test temperature of 19°C (to reveal the effects of acclimation). AP duration (APD) was prolonged in cold-acclimated (CA) cardiomyocytes tested at 14°C compared with 19°C and in warm-acclimated (WA) cardiomyocytes tested at 19°C compared with 24°C. This effect was mirrored by a decrease in the density of the delayed-rectifier current (I_Kr), whereas the density of the background inward-rectifier current (I_K1) was unchanged. When CA and WA cardiomyocytes were tested at a common temperature of 19°C, no significant effects of temperature acclimation on AP shape or duration were observed, whereas I_Kr density was markedly increased in CA cardiomyocytes. I_K1 density was unaffected in CA ventricular myocytes but was significantly reduced in CA atrial myocytes, resulting in a depolarization of atrial resting membrane potential. Our results indicate the bluefin AP is relatively short compared with other teleosts, which may allow the bluefin heart to function at cold temperatures without the necessity for thermal compensation of APD.

thermal acclimation; bluefin tuna; cardiac; potassium ion channels; action potential