Ca2+ oscillations regulated by Na+-Ca2+ exchanger and plasma membrane Ca2+ pump induce fluctuations of membrane currents and potentials in human mesenchymal stem cells

Human bone marrow-derived mesenchymal stem cells (hMSCs) have the potential to differentiate into several types of cells. We have demonstrated spontaneous [Ca2+](i) oscillations in hMSCs without agonist stimulation, which result primarily from release of Ca2+ from intracellular stores via InsP(3) receptors. In this study, we further investigated functions and contributions of Ca2+ transporters on plasma membrane to generate [Ca2+](i) oscillations. In confocal Ca2+ imaging experiments, spontaneous [Ca2+](i) oscillations were observed in 193 of 280 hMSCs. The oscillations did not sustain in the Ca2+ free solution and were completely blocked by the application of 0.1 mM La3+. When plasma membrane Ca2+ pumps (PMCAs) were blocked with blockers, carboxyeosin or caloxin, [Ca2+](i), oscillations were inhibited. Application of Ni2+ or KBR7943 to block Na+-Ca2+ exchanger (NCX) also inhibited [Ca2+](i) oscillations. Using RT-PCR, mRNAs were detected for PMCA type IV and NCX, but not PMCA type II. In the patch clamp experiments, Ca2+ activated outward K+ currents (I-KCa) with a conductance of 170 +/- 21.6 pS could be recorded. The amplitudes Of I-KCa and membrane potential (V-m) periodically fluctuated liked to [Ca2+](i) oscillations. These results suggest that in undifferentiated hMSCs both Ca2+ entry through plasma membrane and Ca2+ extrusion via PMCAs and NCXs play important roles for [Ca2+](i) oscillations, which modulate the activities Of I-KCa to produce the fluctuation of V-m. (C) 2003 Elsevier Science Ltd. All rights reserved.