Characterization of Ca2+ signaling pathways in human mesenchymal stem cells

Human mesenchymal stem cells (HMSC) have the potential to differentiate into many cell types. The physiological properties of HMSCs including their Ca2+ signaling pathways, however, are not well understood. We investigated Ca2+ influx and release functions in HMSCs. In Ca2+ imaging experiments, spontaneous Ca2+ oscillations were observed in 36 of 50 HMSCs. The Ca2+ oscillations were completely blocked by the application of 10 muM cyclopiazonic acid (CPA) or 1 muM thapsigargin (TG). A brief application of 1 muM acetylcholine (ACh) induced a transient increase of [Ca2+](i) but the application of caffeine (10 mM) did not induce any Ca2+ transient. When the stores were depleted with Ca2+-ATPase blockers (CPA or TG) or muscarinic agonists (ACh), store-operated Ca2+ (SOC) entry was observed. Using the patch-clamp technique, store-operated Ca2+ currents (I-SOC) could be recorded in cells treated with ACh or CPA, but voltage-operated Ca2+ currents (VOCCs) were not elicited in most of the cells (17/20), but in 15% of cells examined, small dihydropyridine (DHP)-sensitive Ca2+ Currents were recorded. Using RT-PCR, mRNAs were detected for inositol 1,4,5-trisphosphate receptor (InsP(3)R) type I, II, and III and DHP receptors alpha1A and alpha1H were detected, but mRNA was not detected for ryanodine receptor (RyR) or N-type Ca2+ channels. These results suggest that in undifferentiated HMSCs, Ca2+ release is mediated by InsP(3)Rs and Ca2+ entry through plasma membrane is mainly mediated by the SOCs channels with a little contribution of VOCCs. (C) 2002 Elsevier Science Ltd. All rights reserved.