Mechanisms of Isoform-Specific Na/K Pump Regulation by Short- and Long-Term Adrenergic Activation in Rat Ventricular Myocytes

Abstract

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), α-isoform mRNA, and α-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 α₁-isoform translocation from the membrane to early endosomes, and noradrenaline increased the I_PH through a PKC-dependent pathway that involves α₂-isoform translocation from late endosomes to the membrane. After long-term incubation, isoprenaline increased the I_PL, α₁-isoform mRNA, and α₁-isoform protein, and noradrenaline reduced the I_PH, α₂-isoform mRNA, and α₁-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 α-isoform, whereas short-term regulation involves the translocation of the available α-isoform to the plasma membrane.