Figure 4. TLR2 regulates APD through production of IL-1β by cardiac macrophages.

(a) Experimental protocol: macrophages from rat hearts were depleted with clodronate liposomes (clodronate-L). After depletion, cardiac muscle strips were incubated with TLR2 agonist Pam3 (1 μg ml⁻¹). Liposomes containing PBS were used as control vehicle solution (Liposomes). (b) Enzyme-linked immunosorbent assay quantification of IL-1β cardiac content (graph represents three independent experiments in duplicate, n=6 hearts per group). (c) Experimental protocol: rat cardiac muscle strips were incubated for 24 h with Pam3 (1 μg ml⁻¹) in the presence or absence of the IL-1 receptor antagonist IL-1ra (100 ng ml⁻¹) and electrical function was assessed (n of cells=Control: 10; Pam3: 7; Pam3+IL-1ra: 7; IL-1β: 14; IL-1β+IL-1ra: 12; from four hearts). (d) Representative action potential (AP) traces from endocardial layer of left ventricle strips at 300 ms basic cycle length (BCL). (e) The graph summarizes the APD₉₀ values from endocardial layer of left ventricle strips at 300 ms BCL under different condition. (f,g) Representative AP traces (left panel) and APD₉₀ values (right panel) in rats cardiac strips from animals pre-treated with clodronate liposomes or control liposomes and then exposed 24 h to Pam3 (n=Control: 10; Pam3+liposomes: four hearts ; Pam3+clodronate-L: six hearts). The results are expressed as mean±s.e.m. Scatter plots show values from individual cell preparations, where horizontal bars represent means and error bars, s.e.m. # and ## represents, respectively P<0.05 and P<0.01 (Bonferroni's post test following one-way ANOVA).