FIGURE 6.

Effect of isoproterenol stimulation in PMCA4^−/− mice. A, dose response to isoproterenol following administration of 0. 025, 0.1, 0.4, and 1.6 mg/kg of isoproterenol in PMCA4^−/− and their WT littermates. The left panel shows absolute values for dP/dt_max, and the right panel shows changes in contractile function (ΔdP/dt_max) in response to various doses of isoproterenol. The response to 1.6 mg/kg of isoproterenol injection was significantly attenuated in PMCA4^−/− mice when compared with their WT littermates (n = 10, *, p < 0.05). mg/kg BW, mg/kg of body weight. B, representative calcium transient traces from isolated PMCA4^−/− and WT myocytes at baseline and after stimulation with isoproterenol (Iso, 100 nm). C, quantification of the change in calcium transient amplitude after isoproterenol (100 nm) perfusion indicated that PMCA4^−/− cardiomyocytes showed a significantly reduced response to isoproterenol stimulation (*, p < 0.05 versus WT, n = 10–12 myocytes from 4–5 independent animals in each group).