Mechanisms of isoform-specific Na/K pump regulation by short- and long-term adrenergic activation in rat ventricular myocytes.

Background: Many stressful conditions, including cardiovascular diseases, induce long-term elevations in circulating catecholamines, thereby leading to changes of the Na/K pump and thus affecting myocardial functions. However, only short-term adrenergic regulation of the Na/K pump has been reported. The present study is the first investigation of long-term adrenergic regulation of the Na/K pump and the potential mechanism. Methods: After acutely isolated Sprague-Dawley rat myocytes were incubated with noradrenaline or isoprenaline for 24 h, Na/K pump high- (I-PH) and low affinity current (I-PL), alpha-isoform mRNA, and alpha-isoform protein were examined using patch clamp, RT-PCR, and Western blotting techniques, respectively. Results: After the short-term incubation, isoprenaline reduced the I-PL through a PKA-dependent pathway that involves alpha(1)-isoform translocation from the membrane to early endosomes, and noradrenaline increased the I-PH through a PKC-dependent pathway that involves alpha(2)-isoform translocation from late endosomes to the membrane. After long-term incubation, isoprenaline increased the I-PL, alpha(1)-isoform mRNA, and alpha(1)-isoform protein, and noradrenaline reduced the I-PH, alpha(2)-isoform mRNA, and alpha(1)-isoform protein through a PKA- or PKC-dependent pathway, respectively. Conclusions: These results suggest that long-term adrenergic Na/K pump regulation is isoform-specific and negatively feeds back on the short-term response. Furthermore, long-term regulation involves transcription and translation of the respective alpha-isoform, whereas short-term regulation involves the translocation of the available alpha-isoform to the plasma membrane. Copyright (C) 2014 S. Karger AG, Basel