Diabetes mellitus with hyperglycaemia is a major risk factor for malignant cardiac dysrhythmias. However, the underlying mechanisms remain unclear, especially during the embryonic developmental phase of the heart. This study investigated the effect of hyperglycaemia on the pulsatile activity of stem cell-derived cardiomyocytes. Mouse embryonic stem cells (mESCs) were differentiated into cardiac-like cells through embryoid body (EB) formation, in either baseline glucose or high glucose conditions. Action potentials (APs) were recorded using a voltage-sensitive fluorescent dye and gap junction activity was evaluated using scrape-loading lucifer yellow dye transfer assay. Molecular components were detected using immunocytochemistry and immunoblot analyses. High glucose decreased the spontaneous beating rate of EBs and shortened the duration of onset of quinidine-induced asystole. Furthermore, it altered AP amplitude, but not AP duration, and had no impact on the expression of the hyperpolarisation-activated cyclic nucleotide-gated isoform 4 (HCN4) channel nor on the EB beating rate response to ivabradine nor isoprenaline. High glucose also decreased both the intercellular spread of lucifer yellow within an EB and the expression of the cardiac gap junction protein connexin 43 as well as upregulated the expression of transforming growth factor beta 1 (TGFβ1) and phosphorylated Smad3. High glucose suppressed the autorhythmicity and gap junction conduction of mESC-derived cardiomyocytes, via mechanisms probably involving TGFβ1/Smad3 signalling. The results allude to glucotoxicity related proarrhythmic effects, with potential clinical implications in foetal diabetic cardiac disease.

Diabetes mellitus with hyperglycaemia is a major risk factor for malignant cardiac dysrhythmias.However, the underlying mechanisms remain unclear, especially during the embryonic developmental phase of the heart. This study investigated the effect of hyperglycaemia on the pulsatile activity of stem cell-derived cardiomyocytes. Mouse embryonic stem cells (mESCs) were differentiated into cardiac-like cells through embryoid body (EB) formation, in either baseline glucose or high glucose conditions. Action potentials (APs) were recorded using a voltage-sensitive uorescent dye and gap junction activity was evaluated using scrape-loading lucifer yellow dye transfer assay. Molecular components were detected using immunocytochemistry and immunoblot analyses. High glucose decreased the spontaneous beating rate of EBs and shortened the duration of onset of quinidine-induced asystole. Furthermore, it altered AP amplitude, but not AP duration, and had no impact on the expression of the hyperpolarisationactivated cyclic nucleotide-gated isoform 4 (HCN4) channel nor on the EB beating rate response to ivabradine nor isoprenaline. High glucose also decreased both the intercellular spread of lucifer yellow within an EB and the expression of the cardiac gap junction protein connexin 43 as well as upregulated the expression of transforming growth factor beta 1 (TGFβ1) and phosphorylated Smad3. High glucose suppressed the autorhythmicity and gap junction conduction of mESC-derived cardiomyocytes, via mechanisms probably involving TGFβ1/Smad3 signalling. The results allude to glucotoxicity related proarrhythmic effects, with potential clinical implications in foetal diabetic cardiac disease.