Human-induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) are a potential source to develop assays for predictive electrophysiological safety screening. Published studies show that the relevant physiology and pharmacology exist but does not show the translation between stem cell cardiomyocyte assays and other preclinical safety screening assays, which is crucial for drug discovery and safety scientists and the regulators. Our studies are the first to show the pharmacology of ion channel blockade and compare them with existing functional cardiac electrophysiology studies. Ten compounds (a mixture of pure hERG [E-4031 and Cisapride], hERG and sodium [Flecainide, Mexiletine, Quinidine, and Terfenadine], calcium channel blockers [Nifedipine and Verapamil], and two proprietary compounds [GSK A and B]) were tested, and results from hiPSC-CMs studied on multielectrode arrays (MEA) were compared with other preclincial models and clinical drug concentrations and effects using integrated risk assessment plots. All ion channel blockers produced (1) functional effects on repolarization and depolarization around the IC25 and IC50 values and (2) excessive blockade of hERG and/or blockade of sodium current precipitated arrhythmias. Our MEA data show that hiPSC-CMs demonstrate relevant pharmacology and show excellent correlations to current functional cardiac electrophysiological studies. Based on these results, MEA assays using iPSC-CMs offer a reliable, cost effective, and surrogate to preclinical in vitro testing, in addition to the 3Rs (refine, reduce, and replace animals in research) benefit.

No abstract

SUMMARYThis research was designed to compare coronary, carotid and aortic arch baroreceptors in terms of the ranges of pressures required to elicit reflex vascular responses and the possible differences between the responses to pulsatile and non-pulsatile stimuli. Dogs were anaesthetized with a-chloralose, artificially ventilated and the chests opened wide. A perfusion circuit allowed independent control of pressures distending the three baroreceptor regions. A cardiopulmonary bypass and ventricular fibrillation prevented cardiac pulsations from influencing coronary baroreceptor pressure. The caudal region of the animal was perfused at constant flow and vascular resistance responses were assessed from changes in perfusion pressure. Only tests in which the overall response exceeded 3 kPa (22.5 mmHg) were analysed. Reflex responses were obtained to significantly lower coronary pressures than were required to induce responses from other regions. The inflexion points of the stimulus-response curves for pulsatile coronary, carotid and aortic pressures were 10.5 + 0 6, 15 5 + 1 8 and 16 4 + 1 7 kPa (79 + 5, 116 + 14 and 123 + 13 mmHg, respectively; values are means + S.E.M.). When the responses to pulsatile stimuli were compared with those to non-pulsatile stimuli, it was noted that for the carotid receptors, lower pressures were required to induce responses (inflexion pressure less) and the slope of the stimulus-response curve was less. Pulsatile aortic pressures induced a parallel (downward) displacement of the curve but no change in inflexion point or slope. The coronary baroreceptor stimulus-response relationship was unaffected by pulsatility. These results show differences between the characteristics of the three baroreceptors with coronary receptors being unaffected by pressure pulsatility but likely to be of importance in hypotensive situations.

No abstract

SUMMARYIn chloralose-anaesthetized dogs, pressures applied to coronary, carotid and aortic baroreceptors were changed independently and the resulting reflex vascular responses were determined. Increases in pressure to each group of baroreceptors resulted in reflex vasodilatation; the maximal responses to distension of carotid and coronary baroreceptors were significantly larger than those to aortic receptors, but not different from each other. Increases in pressure in all three regions induced maximal responses at similar times from the onset of the pressure stimulus. However, the time for recovery of vascular resistance following a decrease in baroreceptor pressure differed. Vasoconstriction following a period of coronary hypertension occurred slowly, requiring 70 s for 90 % of the response to develop. This was significantly longer than the corresponding times for carotid and aortic receptors (about 28 s). The rate of vasoconstriction in response to coronary baroreceptor unloading was influenced by the period for which the pressure stimulus was applied and vasoconstriction was even slower when the pressure stimulus had been maintained for 8 min. The mechanism responsible for delaying the vasoconstriction following a period of coronary hypertension is not known, but this effect may have important implications for the control of arterial blood pressure.