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Figure 2 Concentration-dependent effects of (–)-norepinephrine for changes in contractile force, time to reach peak force, and time to reach 50% relaxation (t₅₀) through activation of Ser49Gly- and Gly389Arg-polymorphisms of the beta₁-adrenergic receptor in human right atrium. Contractile force is expressed in terms of absolute force (mN). Experiments were completed by incubation of tissues with 200 µM (–)-isoproterenol to maximally stimulate both beta₁- and beta₂-adrenergic receptors followed by raising the concentration of Ca²⁺ to 9.25 mM. Values shown are mean ± SEM, where SEM values were determined from each specific –log (–)-norepinephrine concentration. Errors not shown when smaller than symbol. Values in parenthesis show (tissue number/patient number). Arg = arginine; Gly = glycine; Ser = serine.