Its absolute values were approximately 350 fmol/mg cytosolic protein, and its expression was not changed in heart failure. beta-Arrestin-2 levels were too low to be detectable using the same methods. beta ARK levels as determined by enzymatic activity were approximately 20 fmol/mg cytosolic protein (beta ARK-1 plus beta ARK-2) and thus almost 20-fold lower than those of beta-arrestin. beta ARK levels were increased approximately twofold in heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)
In addition, beta ARK enzyme activity assays were performed, and the levels of beta 1- and beta 2-receptors were determined by radioligand binding. beta ARK mRNA levels were increased almost threefold in both forms of heart failure, and beta ARK activity was enhanced. beta 1-Receptor mRNA levels and beta 1-receptor numbers were decreased by approximately 50% in both failing groups, whereas these levels were unaltered for beta 2-receptors.