Fig. 5
Rate profiles and pharmacological stimulation of pacemaker cell clusters (PCC). a Layout of the experimental design for PCC functional characterization using a multi-electrode array (MEA) system. b Representative raw traces from an electrode of a MEA plated with a spontaneously beating PCC showing field potentials at baseline and after change to medium containing the β-adrenergic agonist isoproterenol (ISO, 1 μM). Subsequent muscarinic challenge using carbachol (Cch, 1 μM) significantly slowed the firing rates. c Average firing rates recorded from MEAs demonstrate chronotropic response of PCC to stimulation with autonomic substances (n = 6 per group). d Representative traces of PCC field potentials at baseline and after application of the If inhibitor ivabradine (IVA, 3 μM). e Dose-dependent rate reduction of PCC upon stimulation with IVA (n = 6 per group). f Rate profiles of spontaneously beating PCC (n = 10, purple) compared to co-cultures of PCC and neonatal rat ventricular myocytes (NRVM) (n = 10, blue) over an observation period of 28 days. g Rate response upon ISO stimulation. Co-cultures (n = 10, green) of PCC and NRVM exhibited higher rates and chronotropic response upon ISO stimulation than NRVM monolayers (n = 10, orange) at culture day 4. Data are provided as means ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, pharmacologically stimulated samples versus baseline control; # p < 0.05, ## p < 0.01, ### p < 0.001, PCC samples versus PCC + NRVM co-cultures; comparison between multiple groups was performed using one-way ANOVA followed by a Tukey post-hoc test