Figure 5.

Effect of 5-HT on APD and refractoriness in human atrial cells from patients treated with β-blockers. (a) Representative examples of action potentials recorded from a single human atrial myocyte from a patient treated with a β-blocker, before (upper panel) and in the presence of 5-HT at 10 μM (lower panel). Cells were paced at 75 bpm. Dotted lines in bold show the level of 50% of the action potential amplitude. The ERP, indicated by solid bars, was defined and calculated as in the legend of Figure 4a. (b) Mean (±s.e.m.) APD (APD₅₀ and APD₉₀; n=17 cells, nine patients) and ERP (n=12 cells, nine patients) in cells from patients treated with β-blockers, in the absence (open bars), in the presence (closed bars) and after removal of 10 μM 5-HT (striped bars; n=7 cells, five patients for APD and n=3 cells, three patients for ERP). The asterisk denotes P<0.05 between control and 5-HT values (paired t-test).