Osteoblast-like cells have a variable mixed population of purino/nucleotide receptors

Osteoblast-like UMR 106.06 cells respond to extracellular application of nucleotides with a fast intracellular calcium pulse (latency of about 20 s, half-width of about 10 s), as measured with fluo-3 on a confocal laser scanning system. Cross-inhibition experiments at 50 microM show that, on a cell population basis, adenosine triphosphate (ATP) strongly inhibits the effect of uridine triphosphate (UTP) or 2-methylthio-ATP (2-MeSATP) applied within 2 min after the end of the ATP-induced pulse, while prior application of UTP or 2-MeSATP only weakly inhibits the ATP effect, and UTP and 2-MeSATP weakly inhibit each other. Furthermore, there are clear differences in cross-inhibition between individual cells. Our measurements provide strong evidence that these cells have at least two types of purino/nucleotide receptors, probably P2y and P2u, with a proportion that varies between individual cells.