5-Azacytidine induces changes in electrophysiological properties of human mesenchymal stem cells

Previously,mouse bone marrow-derived stem cells(MSC)treated with the unspecific DNA methyltransferase inhibi-tor 5-azacytidine were reported to differentiate into cardiomyocytes.The aim of the present study was to investigate theefficiency of a similar differentiation strategy in human mononuclear cells obtained from healthy bone marrow donors.After 1-3 passages,cultures were exposed for 24 h to 5-azacytidine(3μM)followed by 6 weeks of further culture.Drug treatment did not induce expression of myogenic marker MyoD or cardiac markers Nkx2.5 and GATA-4 and didnot yield beating cells during follow-up.In patch clamp experiments,approximately 10-15% of treated and untreatedcells exhibited L-type Ca~2+ currents.Almost all cells showed outwardly rectifying K~+ currents of rapid or slow activationkinetics.Mean current amplitude at +60 mV doubled after 6 weeks of treatment compared with time-matched controls.Membrane capacitance of treated cells was significantly larger than in controls 2 weeks after treatment and remained highafter 6 weeks.Expression levels ofmRNAs for the K~+ channels Kv1.1,Kv1.5,Kv2.1,Kv4.3 and KCNMA1 and for theCa~2+ channel Ca1.2 were not affected by 5-azacytidine.Treatment with potassium channel blockers tetraethylammoniumand clofilium at concentrations shown previously to inhibit rapid or slowly activating K~+ currents of hMSC inhibitedproliferation of these cells.Our results suggest that despite the absence of differentiation of hMSC into cardiomyocytes,treatment with 5-azacytidine caused profound changes in current density.