Figure 7. β-AR responsiveness of K⁺ currents in HF.

Dose-response effect of isoproterenol (ISO) on I_Ks, I_Kr and I_K1 peak densities under AP-clamp at 2 Hz. Pipette solution contained 10 mM BAPTA. (A) I_Ks measured as HMR-sensitive current showed a robust accumulation following ISO application. I_KS sensitivity (EC₅₀) to ISO was unchanged in HF, whereas the response was significantly reduced in HF. (B) I_Kr was minimally affected by ISO treatment; however, neither the ISO-sensitivity nor the magnitude of the response were altered in HF. (C) I_K1 peak density did not change following ISO application under buffered [Ca²⁺]_i conditions and I_K1 was uniformly decreased in HF. 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 three to five individual animals. ANOVA with Bonferroni posttest, *p<0.05, **p<0.01, ***p<0.001.