Figure 4.

Expression of cardiac β-ARs and Ca²⁺-handling proteins. Hearts were removed from male (M) and female (F) WT and mstn^−/− pups on the indicated days and equal amounts of protein were analyzed by Western blotting for β1AR and β2ARs, PLN, P-PLN, and SERCA2a. Band intensities for each of these proteins were normalized to those of GAPDH whereas P-PLN was normalized to GAPDH or PLN (P-PLN/G or P-PLN/PLN). Aging mice (D) were 18–24 m.o., and significant differences in all graphs are indicated by asterisks (P ≤ .05, n = 6/group). Comparisons were made between WT and msnt^−/− mice for a particular sex but not between sexes.