Figure 4: β-Adrenergic Activation of PLN in Human Heart Slices

After 1 day in culture, duplicate left ventricular myocardial slices were treated for 15 min with varying doses of the β-adrenergic agonist isoproterenol (ISO), without or with the nonselective β-antagonist propranolol (PROP). Phosphorylation of phospholamban (PLN) at S16 was measured by immunoblot. A and B are from a nonfailing heart. (A) ISO doses. A blot of total PLN (tPLN) shows equal loading. (B) PROP inhibits ISO. (C) Concentration-response relationships for the indicated number of hearts, with duplicate slices for each heart at each dose; mean ± SE. The maximum effect values (Emax) for both failing (21) and nonfailing (17) are different from 1.0 (p < 0.05 by confidence limits). Half-maximal effective concentration (EC50) and Emax values for failing and nonfailing do not differ by curve fitting. These failing patients were treated with a left ventricular assist device.

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