Permissive role of cAMP in the oscillatory Ca2+ response to inositol 1,4,5-trisphosphate in rat hepatocytes.
Rat hepatocytes respond to alpha-adrenergic stimulation by intracellular production of myo-inositol 1,4,5-trisphosphate (IP3) which stimulates the periodic release and reuptake of intracellular store (IS) Ca2+. The generation of these Ca2+ oscillations was investigated by simultaneously monitoring Ca2+ changes in the cytosol and IS by combined fluorescence microscopy and whole-cell patch clamp. Intracellular IP3 perfusion (1-50 microM in the pipette) produced three types of Ca2+ response: understimulation, oscillations and overstimulation, i.e. with Ca2+ levels not returning to baseline. In a total of 57 experiments, only three displayed oscillations during continuous IP3 infusion, in a narrow range of IP3 concentration centred around 5-8 microM in the pipette. In oscillating cells, cytosolic Ca2+ spikes were synchronized with transient Ca2+ depletions of the IS, consistent with a direct exchange of Ca2+ between the two compartments. Application of 8-Br-cAMP to cells infused with IP3 increased the probability of eliciting Ca2+ oscillations by a factor of 4-5 for IP3 concentrations in the range 1-10 microM, whereas IP3 concentrations above 10 microM always resulted in overstimulation. IP3 photorelease experiments and measurements of IS Ca2+ content indicated that 8-Br-cAMP enhanced the affinity of the IP3 receptor and increased the pool of releasable Ca2+. We propose that cAMP has a permissive role in the generation of IP3-induced Ca2+ oscillations by extending the window of IP3 concentrations able to elicit oscillations.
Chatton
J Y
JY
Institute of Pharmacology, University of Berne, Friedbuhlstrasse 49, CH-3010 Berne, Switzerland.
Cao
Y
Y
Liu
H
H
Stucki
J W
JW
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009991:Oscillometry; D051381:Rats; D017208:Rats, Wistar
D015124:8-Bromo Cyclic Adenosine Monophosphate; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium