Effect of STA on cAMP content and PKA activation changes induced by NE. Quantification of intracellular (A) cAMP content and (B) PKA activation. The luminescence intensity and fluorescence intensity are inversely correlated with cAMP content and PKA activation. The data are expressed as the mean ± SEM. n = 4. *P < 0.05 versus control, #P < 0.05 versus NE. NE: norepinephrine, CAR: carvedilol, STA: stachydrine, PLN: phospholamban.