Effects of extracellular nucleotides on single cells and populations of human osteoblasts: contribution of cell heterogeneity to relative potencies.
1. Human osteoblasts responded to the application of extracellular nucleotides, acting at P2-receptors, with increases in cytosolic free calcium concentration ([Ca2+]i). 2. In populations of human osteoblasts, adenosine 5'-diphosphate (ADP) evoked a rise in [Ca2+]i with less than 40% of the amplitude of that induced by adenosine 5'-triphosphate (ATP). 3. ATP and uridine 5'-triphosphate (UTP) were applied to single human osteoblasts and induced [Ca2+]i rises of comparable amplitude in every cell tested. 4. However, from the results of single cell studies with ADP (and 2-methylthioATP (2-meSATP)) two groups of cells were delineated; one group responded to ADP (or 2-meSATP) with a rise in [Ca2+]i indistinguishable from that evoked by ATP; whereas the second group failed completely to respond to ADP (or 2-meSATP). 5. Therefore heterogeneity of receptor expression exists within this population of human osteoblasts. The limited distribution of the ADP-responsive receptor underlies the small response to ADP, compared with ATP, recorded in populations of human osteoblasts. This heterogeneity may reflect differences in the differentiation status of individual cells.
Dixon
C J
CJ
Department of Human Anatomy and Cell Biology, New Medical School, University of Liverpool.
Bowler
W B
WB
Walsh
C A
CA
Gallagher
J A
JA
D000227:Adenine Nucleotides / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000187:drug effects* / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology*
D000227:Adenine Nucleotides; D018048:Receptors, Purinergic P2; D002118:Calcium; D014544:Uridine Triphosphate