A cADP-ribose antagonist does not inhibit secretagogue-, caffeine- and nitric oxide-induced Ca2+ responses in rat pancreatic beta-cells.
It is controversial whether the Ca2+ mobilizing agent, cADP-ribose (cADPR), is implicated in secretagogue-mediated intracellular Ca2+ responses of pancreatic beta-cells. In this study we utilised a potent antagonist of cADPR, 8-amino-cADPR, to determine whether cADPR is involved in glucose-, acetylcholine-, caffeine- and nitric oxide-induced intracellular Ca2+ responses of isolated rat beta-cells. The antagonist was found to be effective in the complete inhibition of cADPR-induced Ca2+ release from sea urchin egg microsome preparations, when used at equivalent concentrations to cADPR (between 0.1-10 microM) in the assay. Isolated beta-cells were co-loaded with up to 50 microM 8-amino-cADPR, and Fura-2 or Fluo-3, by the whole-cell patch technique. At this concentration, the antagonist failed to affect standard glucose- and acetylcholine-induced increases in the intracellular free Ca2+ ([Ca2+]i) of isolated rat pancreatic beta-cells, as assessed by video ratio imaging and single wavelength microfluorimetry. Applying the same methodology, the antagonist also failed to affect NO- and caffeine-induced intracellular Ca2+ responses of rat beta-cells. These results suggest that cADPR does not appear to play a fundamental role in beta-cell Ca2+ signalling. As a control, patch-loading with heparin (2 mg/ml) however, abolished the acetylcholine response but neither affected the NO- or caffeine-induced mobilization of intracellular Ca2+. These results support the involvement of the IP3-receptor in acetylcholine-induced mobilization of intracellular Ca2+, but not that invoked by caffeine.
Willmott
N J
NJ
Department of Pharmacology, University of Oxford, UK.
Galione
A
A
Smith
P A
PA
D000109:Acetylcholine / Q000494:pharmacology; D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D036563:Cyclic ADP-Ribose / Q000031:analogs & derivatives; D017136:Ion Transport / Q000187:drug effects; D009569:Nitric Oxide / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D002121:Calcium Channel Blockers; D036563:Cyclic ADP-Ribose; C082175:8-aminoadenosine cyclic 3',5'-(hydrogen phosphate) 5'-ribofuranosyl ester; D000246:Adenosine Diphosphate Ribose; D009569:Nitric Oxide; D002110:Caffeine; D000109:Acetylcholine; D002118:Calcium