Zinc Alters Ractopamine HCl Response in Cultured Skeletal Muscle Cells

The objective of this study was to determine if zinc, when added in combination with ractopamine hydrochloride (RH), would stabilize the interaction of RH with the β-adrenergic receptor, as indicated by altered cAMP concentrations, mRNA quantity, or protein abundance. Cultured bovine skeletal muscle cells were established and treated after 120 h for 6, 24, and 96 h with differentiation media of specific treatments. Treatments were applied in a factorial arrangement with two levels of zinc (0 μM or 1 μM) and two levels of RH (0 μM or 10 μM) in differentiation media. cAMP levels were measured at 6, 24, and 96 h, while mRNA and protein were measured at 24 and 96 h. At 6 h, no differences (P > 0.05) were detected in cAMP levels between the treatments. However, at 24 h the 10 μM RH, 1 μM zinc treatment had the greatest concentrations of cAMP (P < 0.05). At 96 h the 10 μM RH, 0 μM zinc treatment had a lower concentration of cAMP (P = 0.05) compared to the control. No differences were detected in mRNA (β1-adrenergic receptor, β2-adenergic receptor, AMPKα, myosin heavy chain I, myosin heavy chain IIA, and myosin heavy chain IIX) concentrations between treatments. Protein quantity of the β1-adrenergic receptor and β2-adrenergic receptor did not differ between treatments. These results indicate that zinc, in combination with RH, may help sustain the RH response during prolonged exposure as indicated by increased cAMP concentrations.