Figure 7.

β-adrenergic receptor (βAR) responsiveness of inward currents in heart failure (HF). Dose-response effect of isoproterenol (ISO) on late Na⁺ current (I_NaL) and L-type Ca²⁺ current (I_CaL) peak densities under AP-clamp at 2 Hz pacing rate. Pipette solution contained 10 mmol/L BAPTA (BAPTA_i). A I_NaL measured as GS-967-sensitive current significantly increased after ISO application. I_NaL sensitivity (EC₅₀, half maximal effective concentration) to ISO was slightly reduced in HF, and I_NaL exhibited similar maximal response in HF than in control despite the increased basal I_NaL in HF. B I_CaL measured as nifedipine-sensitive current was markedly increased after ISO treatment; however, the magnitude of the response was significantly blunted in HF with no change in ISO-sensitivity. EC₅₀ values, Hill coefficients and maximum responses were determined by fitting data to the Hill equation, indicated by solid lines. Symbols and bars represent mean±SEM. n refers to the number of cells measured in each group, and the cells in each group came from 3 to 6 individual animals. Analysis of variance (ANOVA) with Bonferroni posttest, *P<0.05, **P<0.01, ***P<0.001.