Ventricular action potential adaptation to regular exercise: role of {beta}-adrenergic and KATP channel function

Regular exercise training is known to affect the action potential duration (APD) and improve heart function, but involvement of β-adrenergic receptor (β-AR) subtypes and/or the ATP-sensitive K+ (KATP) channel is unknown. To address this, female and male Sprague-Dawley rats were randomly assigned to voluntary wheel-running or control groups; they were anesthetized after 6–8 wk of training, and myocytes were isolated. Exercise training significantly increased APD of apex and base myocytes at 1 Hz and decreased APD at 10 Hz. Ca2+ transient durations reflected the changes in APD, while Ca2+ transient amplitudes were unaffected by wheel running. The nonselective β-AR agonist isoproterenol shortened the myocyte APD, an effect reduced by wheel running. The isoproterenol-induced shortening of APD was largely reversed by the selective β1-AR blocker atenolol, but not the β2-AR blocker ICI 118,551, providing evidence that wheel running reduced the sensitivity of the β1-AR. At 10 Hz, the KATP channel inhibitor glibenclamide prolonged the myocyte APD more in exercise-trained than control rats, implicating a role for this channel in the exercise-induced APD shortening at 10 Hz. A novel finding of this work was the dual importance of altered β1-AR responsiveness and KATP channel function in the training-induced regulation of APD. Of physiological importance to the beating heart, the reduced response to adrenergic agonists would enhance cardiac contra...
Source: Journal of Applied Physiology - Category: Physiology Authors: Tags: RESEARCH ARTICLE Source Type: research