Cell density-dependent changes in intracellular Ca2+ mobilization via the P2Y2 receptor in rat bone marrow stromal cells

✍ Scribed by Jun Ichikawa; Hisae Gemba

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 307 KB
• Volume: 219
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.21680

✦ Synopsis

Abstract

Bone marrow stromal cells (BMSCs) are an interesting subject of research because they have characteristics of mesenchymal stem cells. We investigated intracellular Ca^2+^ signaling in rat BMSCs. Agonists for purinergic receptors increased intracellular Ca^2+^ levels ([Ca^2+^]~i~). The order of potency followed ATP = UTP > ADP = UDP. ATP‐induced rise in [Ca^2+^]~i~ was suppressed by U73122 and suramin, but not by pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulfonic acid (PPADS), suggesting the functional expression of G protein‐coupled P2Y~2~ receptors. RT‐PCR and immunohistochemical studies also showed the expression of P2Y~2~ receptors. [Ca^2+^]~i~ response to UTP changed with cell density. The UTP‐induced rise in [Ca^2+^]~i~ was greatest at high density. V~max~ (maximum Ca^2+^ response) and EC~50~ (agonist concentration that evokes 50% of V~max~) suggest that the amount and property of P2Y~2~ receptors were changed by cell density. Note that UTP induced Ca^2+^ oscillation at only medium cell density. Pharmacological studies indicated that UTP‐induced Ca^2+^ oscillation required Ca^2+^ influx by store‐operated Ca^2+^ entry. Carbenoxolone, a gap junction blocker, enhanced Ca^2+^ oscillation. Immunohistochemical and quantitative real‐time PCR studies revealed that proliferating cell nuclear antigen (PCNA)‐positive cells declined but the mRNA expression level of the P2Y~2~ receptor increased as cell density increased. Co‐application of fetal calf serum with UTP induced Ca^2+^ oscillation at high cell density. These results suggest that the different patterns observed for [Ca^2+^]~i~ mobilization with respect to cell density may be associated with cell cycle progression. J. Cell. Physiol. 219: 372–381, 2009. © 2009 Wiley‐Liss, Inc.