Actions of ADP, but not ATP, on cytosolic free Ca2+ in single rat hepatocytes mimicked by 2-methylthioATP.
1. Aequorin-injected, single rat hepatocytes generate series of repetitive transients in cytosolic free calcium concentration ([Ca2+]i) when stimulated with agonists acting through the phosphoinositide signalling pathway, including ADP and ATP. We have previously described differences in the [Ca2+]i responses of aequorin-injected hepatocytes to ADP and ATP. 2. The effects of the phosphorothioate analogue of ATP, 2-methylthioATP (2-meSATP), have been examined on single rat hepatocytes. This analogue is belived to be the most potent agonist at the P2Y1 subclass of purinoceptor. 3. The [Ca2+]i transients induced by 2-meSATP were indistinguishable from those induced by ADP, and in contrast to those induced by ATP. 4. At hig concentrations, 2-meSATP and ADP both induced transients at high frequency. In contrast, hepatocytes responded to high concentrations of ATP with an initial rapid rise in [Ca2+]i, followed by a slowly decaying fall. 5. The modulatory effects of elevated intracellular cyclic AMP concentration were the same on both 2-meSATP- and ADP-induced [Ca2+]i transients; the peak height and frequency of transients were enhanced. ATP-induced transients, however, underwent either an increase in duration or conversion into a sustained rise in [Ca2+]i. 6. ATP-induced transients were specifically potentiated by the co-addition of alpha, beta-methyleneATP, whereas 2-meSATP- and ADP-induced transients were unaffected by this treatment. 7. We conclude that 2-meSATP acts at the same receptor as ADP on rat hepatocytes, and that this is distinct from teh receptor(s) mediating the effects of ATP.
Dixon
C J
CJ
Dept. of Human Anatomy and Cell Biology, University of Liverpool.
Cobbold
P H
PH
Green
A K
AK
D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D000331:Aequorin / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D058910:Purinergic P2 Receptor Agonists; D051381:Rats; D017208:Rats, Wistar; D013873:Thionucleotides / Q000494:pharmacology*
D058910:Purinergic P2 Receptor Agonists; D013873:Thionucleotides; D000331:Aequorin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium; C008501:2-methylthio-ATP