Coupling of P2Y receptors to Ca mobilization in mesenchymal stromal cells from the human adipose tissue.

The purinergic transduction was examined in mesenchymal stromal cells (MSCs) from the human adipose tissue, and several nucleotides, including ATP, UTP, and ADP, were found to mobilize cytosolic Ca. Transcripts for multiple purinoreceptors were detected in MSC preparations, including A, A, A, P2Y, P2Y, P2Y, P2Y, P2Y, P2Y, P2Y, P2X, P2X, and P2X. Cellular responses to nucleotides were insignificantly sensitive to bath Ca, pointing at a minor contribution of Ca entry, and were suppressed by U73122 and 2-APB, implicating the phosphoinositide cascade in coupling P2Y receptors to Ca release. While individual cells were sensitive to several P2Y agonists, responsiveness to a given nucleotide varied from cell to cell, suggesting that particular MSCs could employ different sets of purinoreceptors. Caged Ca stimulated Ca-induced Ca release (CICR) that was mediated largely by IP receptors, and resultant Ca transients were similar to nucleotide responses by magnitude and kinetics. A variety of findings hinted at CICR to be a universal mechanism that finalizes Ca signaling initiated by agonists in MSCs. Individual MSCs responded to nucleotides in an all-or-nothing manner. Presumably just CICR provided invariant Ca responses observed in MSCs at different nucleotide concentrations. The effects of isoform specific agonists and antagonists suggested that both P2Y and P2Y were obligatory for ADP responses, while P2Y and P2Y served as primary UTP and ATP receptors, respectively. Extracellular NAD stimulated Ca signaling in each ATP-responsive MSC by involving P2Y. The overall data indicate that extracellular nucleotides and NAD can serve as autocrine/paracrine factors regulating MSC functions.