Na+/K+ATPase-Cav1.2 nanodomain differentially regulates intracellular [Na+], [Ca2+] and local adrenergic signaling in cardiac myocytes

Abstract

AbstractBackgroundThe intracellular Na+concentration ([Na+]i) is a crucial but understudied regulator of cardiac myocyte function. The Na+/K+ATPase (NKA) controls the steady-state [Na+]iand thereby determines the set-point for intracellular Ca2+. Here, we investigate the nanoscopic organization and local adrenergic regulation of the NKA macromolecular complex and how it differentially regulates the intracellular Na+and Ca2+homeostases in atrial and ventricular myocytes.MethodsMulticolor STORM super-resolution microscopy, Western Blot analyses, and in vivo examination of adrenergic regulation are employed to examine the organization and function of Na+nanodomains in cardiac myocytes. Quantitative fluorescence microscopy at high spatiotemporal resolution is used in conjunction with cellular electrophysiology to investigate intracellular Na+homeostasis in atrial and ventricular myocytes.ResultsThe NKAα1 (NKAα1) and the L-type Ca2+-channel (Cav1.2) form a nanodomain with a center-to center distance of ∼65 nm in both ventricular and atrial myocytes. NKAα1 protein expression levels are ∼3 fold higher in atria compared to ventricle. 100% higher atrial INKA, produced by large NKA “superclusters”, underlies the substantially lower Na+concentration in atrial myocytes compared to the benchmark values set in ventricular myocytes. The NKA’s regulatory protein phospholemman (PLM) has similar expression levels across atria and ventricle resulting in a much lower PLM/NKAα1 ratio for atrial compared to ventricular tissue. In addition, a huge PLM phosphorylation reserve in atrial tissue produces a high ß-adrenergic sensitivity of INKAin atrial myocytes. ß-adrenergic regulation of INKAis locally mediated in the NKAα1-Cav1.2 nanodomain via A-kinase anchoring proteins.ConclusionsNKAα1, Cav1.2 and their accessory proteins form a structural and regulatory nanodomain at the cardiac dyad. The tissue-specific composition and local adrenergic regulation of this “signaling cloud” is a main regulator of the distinct global intracellular Na+and Ca2+concentrations in atrial and ventricular myocytes.