Involvement of the ryanodine-sensitive Ca2+ store in GLP-1-induced Ca2+ oscillations in insulin-secreting HIT cells.
We investigated intracellular Ca(2+) ([Ca(2+)](i)) oscillations evoked by glucagon-like peptide 1 (GLP-1) in relation to the ryanodine receptor (RyR) and Ca(2+)-induced Ca(2+)release (CICR) mechanism in pancreatic B cell HIT. GLP-1 produced [Ca(2+)](i) oscillations in the cells, both in media with and without Ca(2+), an effect inhibited by ruthenium red and mimicked by 8-Br-cAMPS. In addition, the GLP-1-evoked [Ca(2+)](i) rise was initiated at the local intercellular peripheral cytoplasm, and a resultant expansion of the intercellular space was also observed. Caffeine induced [Ca(2+)](i) elevation in the medium with or without Ca(2+), an effect inhibited by ruthenium red. GLP-1-evoked [Ca(2+)](i) oscillations were also enhanced by IBMX, and eliminated by Rp-8-Br-cAMPS or 20 microM H-89 treatments whereas they were unaffected by 2 microM H-89 treatment. Forskolin caused a transient elevation in [Ca(2+)](i) that was reduced by Rp-8-Br-cAMPS, 2 microM or 20 microM H-89. Our results indicate that GLP-1 initially generated a local [Ca(2+)](i) elevation at the peripheral cytoplasm, subsequently producing [Ca(2+)](i) oscillations that were inhibited by ruthenium red, involving ryanodine-sensitive and cAMP-activated CICR mechanisms. The cytoplasmic levels of cAMP as well as local Ca(2+) might be responsible for [Ca(2+)](i) oscillations.
Sasaki
Sadao
S
Department of Physiology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan. ph1002@hyo-med.ac.jp
Nakagaki
Ikuko
I
Kondo
Hisao
H
Hori
Seiki
S
D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D009991:Oscillometry; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000494:pharmacology*; D011498:Protein Precursors / Q000494:pharmacology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*
D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D019837:Ryanodine Receptor Calcium Release Channel; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium