Dual mechanism for cAMP-dependent modulation of Ca2+ signalling in articular chondrocytes.
The ability of cAMP to modulate the actions of Ca(2+)-mobilizing agonists was studied in single Fura-2-loaded pig articular chondrocytes in primary culture. Forskolin and 8-Br-cAMP increased both the frequency and amplitude of Ca2+ oscillations induced by ATP, and, in unstimulated cells, induced single Ca2+ transients or even Ca2+ oscillations. The cAMP-dependent protein kinase inhibitor H89 totally prevented the effect of cAMP-elevating agents on Ca2+ signalling. Forskolin and 8-Br-cAMP promptly increased the rate of Mn2+ quenching, when administered in the presence of ATP, suggesting a potentiation of receptor-mediated Ca2+ influx. In Ca(2+)-free medium, ATP-induced Ca2+ oscillations decreased and stopped after a few cycles: subsequent ATP additions temporarily resumed the activity, an effect that could be mimicked by forskolin. The same agent induced single Ca2+ transients in 42% of the cell population maintained in Ca(2+)-free medium. Thapsigargin prevented Ca2+ responses to both ATP and forskolin. The results indicate a dual mechanism for cAMP-induced potentiation of Ca2+ signalling in articular chondrocytes: an increase of receptor-mediated Ca2+ influx and a positive modulation of intracellular Ca2+ release.
D'Andrea
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P
Paschini
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V
Vittur
F
F
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002358:Cartilage, Articular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013552:Swine
D005456:Fluorescent Dyes; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D008345:Manganese; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2